prettier/src/printer.js

Prettier is an opinionated JavaScript formatter

"use strict";
var assert = require("assert");
var comments = require("./comments");
var FastPath = require("./fast-path");
var util = require("./util");
var isIdentifierName = require("esutils").keyword.isIdentifierNameES6;
var jsesc = require("jsesc");

var docBuilders = require("./doc-builders");
var concat = docBuilders.concat;
var join = docBuilders.join;
var line = docBuilders.line;
var hardline = docBuilders.hardline;
var softline = docBuilders.softline;
var literalline = docBuilders.literalline;
var group = docBuilders.group;
var multilineGroup = docBuilders.multilineGroup;
var indent = docBuilders.indent;
var conditionalGroup = docBuilders.conditionalGroup;
var ifBreak = docBuilders.ifBreak;

var docUtils = require("./doc-utils");
var hasHardLine = docUtils.hasHardLine;
var getFirstString = docUtils.getFirstString;
var isEmpty = docUtils.isEmpty;

var types = require("ast-types");
var namedTypes = types.namedTypes;
var isString = types.builtInTypes.string;
var isObject = types.builtInTypes.object;

function maybeAddParens(path, lines) {
  return path.needsParens() ? concat([ "(", lines, ")" ]) : lines;
}

function genericPrint(path, options, printPath) {
  assert.ok(path instanceof FastPath);

  var node = path.getValue();
  var parts = [];
  var needsParens = false;
  var linesWithoutParens = genericPrintNoParens(path, options, printPath);

  if (!node || isEmpty(linesWithoutParens)) {
    return linesWithoutParens;
  }

  if (
    node.decorators &&
      node.decorators.length > 0 &&
      // If the parent node is an export declaration, it will be
      // responsible for printing node.decorators.
      !util.getParentExportDeclaration(path)
  ) {
    path.each(
      function(decoratorPath) {
        parts.push(printPath(decoratorPath), line);
      },
      "decorators"
    );
  } else if (
    util.isExportDeclaration(node) &&
      node.declaration &&
      node.declaration.decorators
  ) {
    // Export declarations are responsible for printing any decorators
    // that logically apply to node.declaration.
    path.each(
      function(decoratorPath) {
        parts.push(printPath(decoratorPath), line);
      },
      "declaration",
      "decorators"
    );
  } else {
    // Nodes with decorators can't have parentheses, so we can avoid
    // computing path.needsParens() except in this case.
    needsParens = path.needsParens();
  }

  if (needsParens) {
    parts.unshift("(");
  }

  parts.push(linesWithoutParens);

  if (needsParens) {
    parts.push(")");
  }

  return concat(parts);
}

function genericPrintNoParens(path, options, print) {
  var n = path.getValue();

  if (!n) {
    return "";
  }

  if (typeof n === "string") {
    return n;
  }

  // TODO: For some reason NumericLiteralTypeAnnotation is not
  // printable so this throws, but I think that's a bug in ast-types.
  // This assert isn't very useful though.
  // namedTypes.Printable.assert(n);
  var parts = [];
  switch (n.type) {
    case "File":
      return path.call(print, "program");
    case "Program":
      // Babel 6
      if (n.directives) {
        path.each(
          function(childPath) {
            parts.push(print(childPath), ";", hardline);
          },
          "directives"
        );
      }

      parts.push(
        path.call(
          function(bodyPath) {
            return printStatementSequence(bodyPath, options, print);
          },
          "body"
        )
      );

      parts.push(hardline);

      return concat(parts);
    // Babel extension.
    case "Noop":
    case "EmptyStatement":
      return "";
    case "ExpressionStatement":
      return concat([ path.call(print, "expression"), ";" ]);
    case // Babel extension.
    "ParenthesizedExpression":
      return concat([ "(", path.call(print, "expression"), ")" ]);
    case "AssignmentExpression":
      return group(
        concat([
          path.call(print, "left"),
          " ",
          n.operator,
          " ",
          path.call(print, "right")
        ])
      );
    case "BinaryExpression":
    case "LogicalExpression": {
      const parts = [];
      printBinaryishExpressions(path, parts, print, options);

      return group(
        concat([
          // Don't include the initial expression in the indentation
          // level. The first item is guaranteed to be the first
          // left-most expression.
          parts.length > 0 ? parts[0] : "",
          indent(options.tabWidth, concat(parts.slice(1)))
        ])
      );
    }
    case "AssignmentPattern":
      return concat([
        path.call(print, "left"),
        " = ",
        path.call(print, "right")
      ]);
    case "MemberExpression": {
      return concat([
        path.call(print, "object"),
        printMemberLookup(path, print)
      ]);
    }
    case "MetaProperty":
      return concat([
        path.call(print, "meta"),
        ".",
        path.call(print, "property")
      ]);
    case "BindExpression":
      if (n.object) {
        parts.push(path.call(print, "object"));
      }

      parts.push("::", path.call(print, "callee"));

      return concat(parts);
    case "Path":
      return join(".", n.body);
    case "Identifier":
      return concat([
        n.name,
        n.optional ? "?" : "",
        path.call(print, "typeAnnotation")
      ]);
    case "SpreadElement":
    case "SpreadElementPattern":
    // Babel 6 for ObjectPattern
    case "RestProperty":
    case "SpreadProperty":
    case "SpreadPropertyPattern":
    case "RestElement":
      return concat([
        "...",
        path.call(print, "argument"),
        path.call(print, "typeAnnotation")
      ]);
    case "FunctionDeclaration":
    case "FunctionExpression":
      if (n.async) parts.push("async ");

      parts.push("function");

      if (n.generator) parts.push("*");

      if (n.id) {
        parts.push(" ", path.call(print, "id"));
      }

      parts.push(
        path.call(print, "typeParameters"),
        multilineGroup(
          concat([
            printFunctionParams(path, print, options),
            printReturnType(path, print)
          ])
        ),
        " ",
        path.call(print, "body")
      );

      return concat(parts);
    case "ArrowFunctionExpression":
      if (n.async) parts.push("async ");

      if (n.typeParameters) {
        parts.push(path.call(print, "typeParameters"));
      }

      if (
        n.params.length === 1 &&
          !n.rest &&
          n.params[0].type === "Identifier" &&
          !n.params[0].typeAnnotation &&
          !n.predicate &&
          !n.returnType
      ) {
        parts.push(path.call(print, "params", 0));
      } else {
        parts.push(
          multilineGroup(
            concat([
              printFunctionParams(path, print, options),
              printReturnType(path, print)
            ])
          )
        );
      }

      parts.push(" =>");

      const body = path.call(print, "body");
      const collapsed = concat([ concat(parts), " ", body ]);

      if (
        n.body.type === "ArrayExpression" ||
          n.body.type === "ObjectExpression" ||
          n.body.type === "JSXElement"
      ) {
        return group(collapsed);
      }

      return conditionalGroup([
        collapsed,
        concat([
          concat(parts),
          indent(options.tabWidth, concat([ line, body ]))
        ])
      ]);
    case "MethodDefinition":
      if (n.static) {
        parts.push("static ");
      }

      parts.push(printMethod(path, options, print));

      return concat(parts);
    case "YieldExpression":
      parts.push("yield");

      if (n.delegate) parts.push("*");

      if (n.argument) parts.push(" ", path.call(print, "argument"));

      return concat(parts);
    case "AwaitExpression":
      parts.push("await");

      if (n.all) parts.push("*");

      if (n.argument) parts.push(" ", path.call(print, "argument"));

      return concat(parts);
    case "ModuleDeclaration":
      parts.push("module", path.call(print, "id"));

      if (n.source) {
        assert.ok(!n.body);

        parts.push("from", path.call(print, "source"));
      } else {
        parts.push(path.call(print, "body"));
      }

      return join(" ", parts);
    case "ImportSpecifier":
      if (n.imported) {
        parts.push(path.call(print, "imported"));

        if (n.local && n.local.name !== n.imported.name) {
          parts.push(" as ", path.call(print, "local"));
        }
      } else if (n.id) {
        parts.push(path.call(print, "id"));

        if (n.name) {
          parts.push(" as ", path.call(print, "name"));
        }
      }

      return concat(parts);
    case "ExportSpecifier":
      if (n.local) {
        parts.push(path.call(print, "local"));

        if (n.exported && n.exported.name !== n.local.name) {
          parts.push(" as ", path.call(print, "exported"));
        }
      } else if (n.id) {
        parts.push(path.call(print, "id"));

        if (n.name) {
          parts.push(" as ", path.call(print, "name"));
        }
      }

      return concat(parts);
    case "ExportBatchSpecifier":
      return "*"
    case "ImportNamespaceSpecifier":
      parts.push("* as ");

      if (n.local) {
        parts.push(path.call(print, "local"));
      } else if (n.id) {
        parts.push(path.call(print, "id"));
      }

      return concat(parts);
    case "ImportDefaultSpecifier":
      if (n.local) {
        return path.call(print, "local");
      }

      return path.call(print, "id");
    case "ExportDeclaration":
    case "ExportDefaultDeclaration":
    case "ExportNamedDeclaration":
      return printExportDeclaration(path, options, print);
    case "ExportAllDeclaration":
      parts.push("export *");

      if (n.exported) {
        parts.push(" as ", path.call(print, "exported"));
      }

      parts.push(" from ", path.call(print, "source"), ";");

      return concat(parts);
    case "ExportNamespaceSpecifier":
      return concat([ "* as ", path.call(print, "exported") ]);
    case "ExportDefaultSpecifier":
      return path.call(print, "exported");
    case "ImportDeclaration":
      parts.push("import ");

      if (n.importKind && n.importKind !== "value") {
        parts.push(n.importKind + " ");
      }

      if (n.specifiers && n.specifiers.length > 0) {
        var standalones = [];
        var grouped = [];

        path.each(
          function(specifierPath) {
            var value = specifierPath.getValue();
            if (
              namedTypes.ImportDefaultSpecifier.check(value) ||
                namedTypes.ImportNamespaceSpecifier.check(value)
            ) {
              standalones.push(print(specifierPath));
            } else {
              grouped.push(print(specifierPath));
            }
          },
          "specifiers"
        );

        assert.ok(standalones.length <= 1);

        if (standalones.length > 0) {
          parts.push(standalones[0]);
        }

        if (standalones.length > 0 && grouped.length > 0) {
          parts.push(", ");
        }

        if (grouped.length > 0) {
          parts.push(
            multilineGroup(
              concat([
                "{",
                indent(
                  options.tabWidth,
                  concat([
                    options.bracketSpacing ? line : softline,
                    join(concat([ ",", line ]), grouped)
                  ])
                ),
                ifBreak(options.trailingComma ? "," : ""),
                options.bracketSpacing ? line : softline,
                "}"
              ])
            )
          );
        }

        parts.push(" from ");
      }

      parts.push(path.call(print, "source"), ";");

      return concat(parts);
    case "BlockStatement":
      var naked = path.call(
        function(bodyPath) {
          return printStatementSequence(bodyPath, options, print);
        },
        "body"
      );

      const hasContent = getFirstString(naked);
      const hasDirectives = n.directives && n.directives.length > 0;

      parts.push("{");

      // Babel 6
      if (hasDirectives) {
        path.each(
          function(childPath) {
            parts.push(
              indent(
                options.tabWidth,
                concat([ hardline, print(childPath), ";" ])
              )
            );
          },
          "directives"
        );
      }

      if (hasContent) {
        parts.push(indent(options.tabWidth, concat([ hardline, naked ])));
      }
      else if(n.comments) {
        parts.push(
          indent(
            options.tabWidth,
            comments.printDanglingComments(path, print, options)
          )
        );
      }

      parts.push(hardline, "}");

      return concat(parts);
    case "ReturnStatement":
      parts.push("return");

      if (n.argument) {
        parts.push(" ", path.call(print, "argument"));
      }

      parts.push(";");

      return concat(parts);
    case "CallExpression": {
      const parent = path.getParentNode();
      // We detect calls on member lookups and possibly print them in a
      // special chain format. See `printMemberChain` for more info.
      if (n.callee.type === "MemberExpression") {
        const printed = printMemberChain(n, options, print);
        if (printed) {
          return printed;
        }
      }

      return concat([
        path.call(print, "callee"),
        printArgumentsList(path, options, print)
      ]);
    }

    case "ObjectExpression":
    case "ObjectPattern":
    case "ObjectTypeAnnotation":
      var allowBreak = false;
      var isTypeAnnotation = n.type === "ObjectTypeAnnotation";
      // Leave this here because we *might* want to make this
      // configurable later -- flow accepts ";" for type separators
      var separator = isTypeAnnotation ? "," : ",";
      var fields = [];
      var leftBrace = n.exact ? "{|" : "{";
      var rightBrace = n.exact ? "|}" : "}";

      if (isTypeAnnotation) {
        fields.push("indexers", "callProperties");
      }

      fields.push("properties");

      var i = 0;
      var props = [];

      fields.forEach(function(field) {
        path.each(
          function(childPath) {
            props.push(group(print(childPath)));
          },
          field
        );
      });

      if (props.length === 0) {
        return "{}";
      } else {
        return multilineGroup(
          concat([
            leftBrace,
            indent(
              options.tabWidth,
              concat([
                options.bracketSpacing ? line : softline,
                join(concat([ separator, line ]), props)
              ])
            ),
            ifBreak(options.trailingComma ? "," : ""),
            options.bracketSpacing ? line : softline,
            rightBrace,
            path.call(print, "typeAnnotation")
          ])
        );
      }

    case "PropertyPattern":
      return concat([
        path.call(print, "key"),
        ": ",
        path.call(print, "pattern")
      ]);
    // Babel 6
    case "ObjectProperty":
    case // Non-standard AST node type.
    "Property":
      if (n.method || n.kind === "get" || n.kind === "set") {
        return printMethod(path, options, print);
      }

      if (n.shorthand) {
        parts.push(path.call(print, "value"));
      } else {
        if (n.computed) {
          parts.push("[", path.call(print, "key"), "]");
        } else {
          parts.push(printPropertyKey(path, options, print));
        }
        parts.push(": ", path.call(print, "value"));
      }

      return concat(parts);
    case // Babel 6
    "ClassMethod":
      if (n.static) {
        parts.push("static ");
      }

      parts = parts.concat(printObjectMethod(path, options, print));

      return concat(parts);
    case // Babel 6
    "ObjectMethod":
      return printObjectMethod(path, options, print);
    case "Decorator":
      return concat([ "@", path.call(print, "expression") ]);
    case "ArrayExpression":
    case "ArrayPattern":
      if (n.elements.length === 0) {
        parts.push("[]");
      } else {
        // JavaScript allows you to have empty elements in an array which
        // changes its length based on the number of commas. The algorithm
        // is that if the last argument is null, we need to force insert
        // a comma to ensure JavaScript recognizes it.
        //   [,].length === 1
        //   [1,].length === 1
        //   [1,,].length === 2
        //
        // Note that util.getLast returns null if the array is empty, but
        // we already check for an empty array just above so we are safe
        const needsForcedTrailingComma = util.getLast(n.elements) === null;

        parts.push(
          multilineGroup(
            concat([
              "[",
              indent(
                options.tabWidth,
                concat([
                  options.bracketSpacing ? line : softline,
                  join(concat([ ",", line ]), path.map(print, "elements"))
                ])
              ),
              needsForcedTrailingComma ? "," : "",
              ifBreak(options.trailingComma ? "," : ""),
              options.bracketSpacing ? line : softline,
              "]"
            ])
          )
        );
      }

      if (n.typeAnnotation) parts.push(path.call(print, "typeAnnotation"));

      return concat(parts);
    case "SequenceExpression":
      return join(", ", path.map(print, "expressions"));
    case "ThisExpression":
      return "this"
    case "Super":
      return "super"
    case // Babel 6 Literal split
    "NullLiteral":
      return "null"
    case // Babel 6 Literal split
    "RegExpLiteral":
      return n.extra.raw;
    // Babel 6 Literal split
    case "NumericLiteral":
      return n.extra.raw;
    // Babel 6 Literal split
    case "BooleanLiteral":
    // Babel 6 Literal split
    case "StringLiteral":
    case "Literal":
      if (typeof n.value === "number") return n.raw;
      if (typeof n.value !== "string") return "" + n.value;

      return nodeStr(n, options);
    case // Babel 6
    "Directive":
      return path.call(print, "value");
    case // Babel 6
    "DirectiveLiteral":
      return nodeStr(n, options);
    case "ModuleSpecifier":
      if (n.local) {
        throw new Error("The ESTree ModuleSpecifier type should be abstract");
      }

      // The Esprima ModuleSpecifier type is just a string-valued
      // Literal identifying the imported-from module.
      return nodeStr(n, options);
    case "UnaryExpression":
      parts.push(n.operator);

      if (/[a-z]$/.test(n.operator)) parts.push(" ");

      parts.push(path.call(print, "argument"));

      return concat(parts);
    case "UpdateExpression":
      parts.push(path.call(print, "argument"), n.operator);

      if (n.prefix) parts.reverse();

      return concat(parts);
    case "ConditionalExpression":
      return group(
        concat([
          path.call(print, "test"),
          indent(
            options.tabWidth,
            concat([
              line,
              "? ",
              path.call(print, "consequent"),
              line,
              ": ",
              path.call(print, "alternate")
            ])
          )
        ])
      );
    case "NewExpression":
      parts.push("new ", path.call(print, "callee"));

      var args = n.arguments;

      if (args) {
        parts.push(printArgumentsList(path, options, print));
      }

      return concat(parts);
    case "VariableDeclaration":
      var printed = path.map(
        function(childPath) {
          return print(childPath);
        },
        "declarations"
      );

      parts = [
        n.kind,
        " ",
        printed[0],
        indent(
          options.tabWidth,
          concat(printed.slice(1).map(p => concat([ ",", line, p ])))
        )
      ];

      // We generally want to terminate all variable declarations with a
      // semicolon, except when they are children of for loops.
      var parentNode = path.getParentNode();

      if (
        !namedTypes.ForStatement.check(parentNode) &&
          !namedTypes.ForInStatement.check(parentNode) &&
          !(namedTypes.ForOfStatement &&
            namedTypes.ForOfStatement.check(parentNode)) &&
          !(namedTypes.ForAwaitStatement &&
            namedTypes.ForAwaitStatement.check(parentNode))
      ) {
        parts.push(";");
      }

      return multilineGroup(concat(parts));
    case "VariableDeclarator":
      return n.init
        ? concat([ path.call(print, "id"), " = ", path.call(print, "init") ])
        : path.call(print, "id");
    case "WithStatement":
      return concat([
        "with (",
        path.call(print, "object"),
        ")",
        adjustClause(path.call(print, "body"), options)
      ]);
    case "IfStatement":
      const con = adjustClause(path.call(print, "consequent"), options);

      parts = [
        "if (",
        group(
          concat([
            indent(
              options.tabWidth,
              concat([ softline, path.call(print, "test") ])
            ),
            softline
          ])
        ),
        ")",
        con
      ];

      if (n.alternate) {
        const hasBraces = isCurlyBracket(con);
        const isEmpty = isEmptyBlock(con);

        if (hasBraces && !isEmpty) {
          parts.push(" else");
        } else {
          parts.push(concat([ hardline, "else" ]));
        }

        parts.push(
          adjustClause(
            path.call(print, "alternate"),
            options,
            n.alternate.type === "IfStatement"
          )
        );
      }

      return group(concat(parts));
    case "ForStatement": {
      const body = adjustClause(path.call(print, "body"), options);

      if (!n.init && !n.test && !n.update) {
        return concat([ "for (;;)", body ]);
      }

      return concat([
        "for (",
        group(
          concat([
            indent(
              options.tabWidth,
              concat([
                softline,
                path.call(print, "init"),
                ";",
                line,
                path.call(print, "test"),
                ";",
                line,
                path.call(print, "update")
              ])
            ),
            softline
          ])
        ),
        ")",
        body
      ]);
    }
    case "WhileStatement":
      return concat([
        "while (",
        group(
          concat([
            indent(
              options.tabWidth,
              concat([ softline, path.call(print, "test") ])
            ),
            softline
          ])
        ),
        ")",
        adjustClause(path.call(print, "body"), options)
      ]);
    case "ForInStatement":
      // Note: esprima can't actually parse "for each (".
      return concat([
        n.each ? "for each (" : "for (",
        path.call(print, "left"),
        " in ",
        path.call(print, "right"),
        ")",
        adjustClause(path.call(print, "body"), options)
      ]);
    case "ForOfStatement":
      return concat([
        "for (",
        path.call(print, "left"),
        " of ",
        path.call(print, "right"),
        ")",
        adjustClause(path.call(print, "body"), options)
      ]);
    case "ForAwaitStatement":
      return concat([
        "for await (",
        path.call(print, "left"),
        " of ",
        path.call(print, "right"),
        ")",
        adjustClause(path.call(print, "body"), options)
      ]);
    case "DoWhileStatement":
      var clause = adjustClause(path.call(print, "body"), options);
      var doBody = concat([ "do", clause ]);
      var parts = [ doBody ];
      const hasBraces = isCurlyBracket(clause);

      if (hasBraces) parts.push(" while");
      else parts.push(concat([ line, "while" ]));

      parts.push(" (", path.call(print, "test"), ");");

      return concat(parts);
    case "DoExpression":
      var statements = path.call(
        function(bodyPath) {
          return printStatementSequence(bodyPath, options, print);
        },
        "body"
      );
      return concat([ "do {\n", statements.indent(options.tabWidth), "\n}" ]);
    case "BreakStatement":
      parts.push("break");

      if (n.label) parts.push(" ", path.call(print, "label"));

      parts.push(";");

      return concat(parts);
    case "ContinueStatement":
      parts.push("continue");

      if (n.label) parts.push(" ", path.call(print, "label"));

      parts.push(";");

      return concat(parts);
    case "LabeledStatement":
      return concat([
        path.call(print, "label"),
        ":",
        hardline,
        path.call(print, "body")
      ]);
    case "TryStatement":
      parts.push("try ", path.call(print, "block"));

      if (n.handler) {
        parts.push(" ", path.call(print, "handler"));
      } else if (n.handlers) {
        path.each(
          function(handlerPath) {
            parts.push(" ", print(handlerPath));
          },
          "handlers"
        );
      }

      if (n.finalizer) {
        parts.push(" finally ", path.call(print, "finalizer"));
      }

      return concat(parts);
    case "CatchClause":
      parts.push("catch (", path.call(print, "param"));

      if (n.guard)
        // Note: esprima does not recognize conditional catch clauses.
        parts.push(" if ", path.call(print, "guard"));

      parts.push(") ", path.call(print, "body"));

      return concat(parts);
    case "ThrowStatement":
      return concat([ "throw ", path.call(print, "argument"), ";" ]);
    // Note: ignoring n.lexical because it has no printing consequences.
    case "SwitchStatement":
      return concat([
        "switch (",
        path.call(print, "discriminant"),
        ") {",
        indent(
          options.tabWidth,
          concat([ hardline, join(hardline, path.map(print, "cases")) ])
        ),
        hardline,
        "}"
      ]);
    case "SwitchCase":
      if (n.test) parts.push("case ", path.call(print, "test"), ":");
      else parts.push("default:");

      if (n.consequent.length > 0) {
        const cons = path.call(
          function(consequentPath) {
            return printStatementSequence(consequentPath, options, print);
          },
          "consequent"
        );

        parts.push(
          isCurlyBracket(cons)
            ? concat([ " ", cons ])
            : indent(options.tabWidth, concat([ hardline, cons ]))
        );
      }

      return concat(parts);
    // JSX extensions below.
    case "DebuggerStatement":
      return "debugger;"
    case "JSXAttribute":
      parts.push(path.call(print, "name"));

      if (n.value) {
        let res;
        if (
          (n.value.type === "StringLiteral" || n.value.type === "Literal") &&
            typeof n.value.value === "string"
        ) {
          res = '"' + util.htmlEscapeInsideDoubleQuote(n.value.value) + '"';
        } else {
          res = path.call(print, "value");
        }
        parts.push("=", res);
      }

      return concat(parts);
    case "JSXIdentifier":
      return "" + n.name;
    case "JSXNamespacedName":
      return join(":", [
        path.call(print, "namespace"),
        path.call(print, "name")
      ]);
    case "JSXMemberExpression":
      return join(".", [
        path.call(print, "object"),
        path.call(print, "property")
      ]);
    case "JSXSpreadAttribute":
      return concat([ "{...", path.call(print, "argument"), "}" ]);
    case "JSXExpressionContainer":
      const shouldIndent =
        n.expression.type !== 'ArrayExpression' &&
        n.expression.type !== 'ObjectExpression' &&
        n.expression.type !== 'ArrowFunctionExpression' &&
        n.expression.type !== 'CallExpression' &&
        n.expression.type !== 'FunctionExpression';

      if (!shouldIndent) {
        return concat(["{", path.call(print, "expression"), "}"]);
      }

      return multilineGroup(
        concat([
          "{",
          indent(
            options.tabWidth,
            concat([ softline, path.call(print, "expression") ])
          ),
          softline,
          "}"
        ])
      );
    case "JSXElement": {
      const elem = printJSXElement(path, options, print);
      return maybeWrapJSXElementInParens(path, elem, options);
    }
    case "JSXOpeningElement":
      return group(
        concat([
          "<",
          path.call(print, "name"),
          multilineGroup(
            concat([
              indent(
                options.tabWidth,
                concat(
                  path.map(attr => concat([ line, print(attr) ]), "attributes")
                )
              ),
              n.selfClosing ? line : softline
            ])
          ),
          n.selfClosing ? "/>" : ">"
        ])
      );
    case "JSXClosingElement":
      return concat([ "</", path.call(print, "name"), ">" ]);
    case "JSXText":
      throw new Error("JSXTest should be handled by JSXElement");
    case "JSXEmptyExpression":
      return "";
    case "TypeAnnotatedIdentifier":
      return concat([
        path.call(print, "annotation"),
        " ",
        path.call(print, "identifier")
      ]);
    case "ClassBody":
      if (n.body.length === 0) {
        return "{}"
      }

      return concat([
        "{",
        indent(
          options.tabWidth,
          concat([
            hardline,
            path.call(
              function(bodyPath) {
                return printStatementSequence(bodyPath, options, print);
              },
              "body"
            )
          ])
        ),
        hardline,
        "}"
      ]);
    case "ClassPropertyDefinition":
      parts.push("static ", path.call(print, "definition"));

      if (!namedTypes.MethodDefinition.check(n.definition)) parts.push(";");

      return concat(parts);
    case "ClassProperty":
      if (n.static) parts.push("static ");

      var key;

      if (n.computed) {
        key = concat([ "[", path.call(print, "key"), "]" ]);
      } else {
        key = printPropertyKey(path, options, print);
        if (n.variance === "plus") {
          key = concat([ "+", key ]);
        } else if (n.variance === "minus") {
          key = concat([ "-", key ]);
        }
      }

      parts.push(key);

      if (n.typeAnnotation) parts.push(path.call(print, "typeAnnotation"));

      if (n.value) parts.push(" = ", path.call(print, "value"));

      parts.push(";");

      return concat(parts);
    case "ClassDeclaration":
    case "ClassExpression":
      return concat(printClass(path, print));
    case "TemplateElement":
      return join(literalline, n.value.raw.split("\n"));
    case "TemplateLiteral":
      var expressions = path.map(print, "expressions");

      parts.push("`");

      path.each(
        function(childPath) {
          var i = childPath.getName();

          parts.push(print(childPath));

          if (i < expressions.length) {
            parts.push("${", expressions[i], "}");
          }
        },
        "quasis"
      );

      parts.push("`");

      return concat(parts);
    // These types are unprintable because they serve as abstract
    // supertypes for other (printable) types.
    case "TaggedTemplateExpression":
      return concat([ path.call(print, "tag"), path.call(print, "quasi") ]);
    case "Node":
    case "Printable":
    case "SourceLocation":
    case "Position":
    case "Statement":
    case "Function":
    case "Pattern":
    case "Expression":
    case "Declaration":
    case "Specifier":
    case "NamedSpecifier":
    // Supertype of Block and Line.
    case "Comment":
    // Flow
    case "MemberTypeAnnotation":
    case // Flow
    "Type":
      throw new Error("unprintable type: " + JSON.stringify(n.type));
    // Babel block comment.
    case "CommentBlock":
    case // Esprima block comment.
    "Block":
      return concat([ "/*", n.value, "*/" ]);
    // Babel line comment.
    case "CommentLine":
    case // Esprima line comment.
    "Line":
      return concat([ "//", n.value ]);
    // Type Annotations for Facebook Flow, typically stripped out or
    // transformed away before printing.
    case "TypeAnnotation":
      if (n.typeAnnotation) {
        if (n.typeAnnotation.type !== "FunctionTypeAnnotation") {
          parts.push(": ");
        }

        parts.push(path.call(print, "typeAnnotation"));

        return concat(parts);
      }

      return "";
    case "TupleTypeAnnotation":
      return concat([ "[", join(", ", path.map(print, "types")), "]" ]);
    case "ExistentialTypeParam":
    case "ExistsTypeAnnotation":
      return "*"
    case "EmptyTypeAnnotation":
      return "empty"
    case "AnyTypeAnnotation":
      return "any"
    case "MixedTypeAnnotation":
      return "mixed"
    case "ArrayTypeAnnotation":
      return concat([ path.call(print, "elementType"), "[]" ]);
    case "BooleanTypeAnnotation":
      return "boolean"
    case "NumericLiteralTypeAnnotation":
    case "BooleanLiteralTypeAnnotation":
      return "" + n.value;
    case "DeclareClass":
      return printFlowDeclaration(path, printClass(path, print));
    case "DeclareFunction":
      return printFlowDeclaration(path, [
        "function ",
        path.call(print, "id"),
        n.predicate ? " " : "",
        path.call(print, "predicate"),
        ";"
      ]);
    case "DeclareModule":
      return printFlowDeclaration(path, [
        "module ",
        path.call(print, "id"),
        " ",
        path.call(print, "body")
      ]);
    case "DeclareModuleExports":
      return printFlowDeclaration(path, [
        "module.exports",
        path.call(print, "typeAnnotation"),
        ";"
      ]);
    case "DeclareVariable":
      return printFlowDeclaration(path, [
        "var ",
        path.call(print, "id"),
        ";"
      ]);
    case "DeclareExportAllDeclaration":
      return concat([ "declare export * from ", path.call(print, "source") ]);
    case "DeclareExportDeclaration":
      return concat([
        "declare ",
        printExportDeclaration(path, options, print)
      ]);
    case "FunctionTypeAnnotation":
      // FunctionTypeAnnotation is ambiguous:
      // declare function foo(a: B): void; OR
      // var A: (a: B) => void;
      var parent = path.getParentNode(0);
      var isArrowFunctionTypeAnnotation = !(!parent.variance &&
        !parent.optional &&
        namedTypes.ObjectTypeProperty.check(parent) ||
        namedTypes.ObjectTypeCallProperty.check(parent) ||
        namedTypes.DeclareFunction.check(path.getParentNode(2)));
      var needsColon = isArrowFunctionTypeAnnotation &&
        namedTypes.TypeAnnotation.check(parent);

      if (needsColon) {
        parts.push(": ");
      }

      parts.push(path.call(print, "typeParameters"));

      parts.push(multilineGroup(printFunctionParams(path, print, options)));

      // The returnType is not wrapped in a TypeAnnotation, so the colon
      // needs to be added separately.
      if (n.returnType || n.predicate) {
        parts.push(
          isArrowFunctionTypeAnnotation ? " => " : ": ",
          path.call(print, "returnType"),
          path.call(print, "predicate")
        );
      }

      return concat(parts);
    case "FunctionTypeParam":
      return concat([
        path.call(print, "name"),
        n.optional ? "?" : "",
        n.name ? ": " : "",
        path.call(print, "typeAnnotation")
      ]);
    case "GenericTypeAnnotation":
      return concat([
        path.call(print, "id"),
        path.call(print, "typeParameters")
      ]);
    case "DeclareInterface":
    case "InterfaceDeclaration": {
      const parent = path.getParentNode(1);
      if (parent && parent.type === "DeclareModule") {
        parts.push("declare ");
      }

      parts.push(
        "interface ",
        path.call(print, "id"),
        path.call(print, "typeParameters"),
        " "
      );

      if (n["extends"].length > 0) {
        parts.push("extends ", join(", ", path.map(print, "extends")), " ");
      }

      parts.push(path.call(print, "body"));

      return concat(parts);
    }
    case "ClassImplements":
    case "InterfaceExtends":
      return concat([
        path.call(print, "id"),
        path.call(print, "typeParameters")
      ]);
    case "IntersectionTypeAnnotation":
    case "UnionTypeAnnotation": {
      const types = path.map(print, "types");
      const op = n.type === "IntersectionTypeAnnotation" ? "&" : "|";

      return conditionalGroup([
        // single-line variation
        // A | B | C
        concat([
          indent(
            options.tabWidth,
            concat([
              types[0],
              indent(
                options.tabWidth,
                concat(types.slice(1).map(t => concat([ " ", op, line, t ])))
              )
            ])
          )
        ]),
        // multi-line variation
        // | A
        // | B
        // | C
        concat([
          indent(
            options.tabWidth,
            concat(types.map(t => concat([ line, op, " ", t ])))
          )
        ])
      ]);
    }
    case "NullableTypeAnnotation":
      return concat([ "?", path.call(print, "typeAnnotation") ]);
    case "NullLiteralTypeAnnotation":
      return "null"
    case "ThisTypeAnnotation":
      return "this"
    case "NumberTypeAnnotation":
      return "number"
    case "ObjectTypeCallProperty":
      if (n.static) {
        parts.push("static ");
      }

      parts.push(path.call(print, "value"));

      return concat(parts);
    case "ObjectTypeIndexer":
      var variance = n.variance === "plus"
        ? "+"
        : n.variance === "minus" ? "-" : "";
      return concat([
        variance,
        "[",
        path.call(print, "id"),
        n.id ? ": " : "",
        path.call(print, "key"),
        "]: ",
        path.call(print, "value")
      ]);
    case "ObjectTypeProperty":
      var variance = n.variance === "plus"
        ? "+"
        : n.variance === "minus" ? "-" : "";
      // TODO: This is a bad hack and we need a better way to know
      // when to emit an arrow function or not.
      var isFunction = !n.variance &&
        !n.optional &&
        n.value.type === "FunctionTypeAnnotation";
      return concat([
        n.static ? "static " : "",
        variance,
        path.call(print, "key"),
        n.optional ? "?" : "",
        isFunction ? "" : ": ",
        path.call(print, "value")
      ]);
    case "QualifiedTypeIdentifier":
      return concat([
        path.call(print, "qualification"),
        ".",
        path.call(print, "id")
      ]);
    case "StringLiteralTypeAnnotation":
      return nodeStr(n, options);
    case "NumberLiteralTypeAnnotation":
      assert.strictEqual(typeof n.value, "number");

      return "" + n.value;
    case "StringTypeAnnotation":
      return "string"
    case "DeclareTypeAlias":
    case "TypeAlias": {
      const parent = path.getParentNode(1);
      if (parent && parent.type === "DeclareModule") {
        parts.push("declare ");
      }

      parts.push(
        "type ",
        path.call(print, "id"),
        path.call(print, "typeParameters"),
        " = ",
        path.call(print, "right"),
        ";"
      );

      return concat(parts);
    }
    case "TypeCastExpression":
      return concat([
        "(",
        path.call(print, "expression"),
        path.call(print, "typeAnnotation"),
        ")"
      ]);
    case "TypeParameterDeclaration":
    case "TypeParameterInstantiation":
      return concat([ "<", join(", ", path.map(print, "params")), ">" ]);
    case "TypeParameter":
      switch (n.variance) {
        case "plus":
          parts.push("+");

          break;
        case "minus":
          parts.push("-");

          break;
        default:
      }

      parts.push(path.call(print, "name"));

      if (n.bound) {
        parts.push(path.call(print, "bound"));
      }

      if (n["default"]) {
        parts.push("=", path.call(print, "default"));
      }

      return concat(parts);
    case "TypeofTypeAnnotation":
      return concat([
        "typeof ",
        path.call(print, "argument")
      ]);
    case "VoidTypeAnnotation":
      return "void";
    case "NullTypeAnnotation":
      return "null";
    case "InferredPredicate":
      return "%checks";
    // Unhandled types below. If encountered, nodes of these types should
    // be either left alone or desugared into AST types that are fully
    // supported by the pretty-printer.
    case "DeclaredPredicate":
      return concat([ "%checks(", path.call(print, "value"), ")" ]);
    // TODO
    case "ClassHeritage":
    // TODO
    case "ComprehensionBlock":
    // TODO
    case "ComprehensionExpression":
    // TODO
    case "Glob":
    // TODO
    case "GeneratorExpression":
    // TODO
    case "LetStatement":
    // TODO
    case "LetExpression":
    // TODO
    case "GraphExpression":
    // TODO
    // XML types that nobody cares about or needs to print.
    case "GraphIndexExpression":
    case "XMLDefaultDeclaration":
    case "XMLAnyName":
    case "XMLQualifiedIdentifier":
    case "XMLFunctionQualifiedIdentifier":
    case "XMLAttributeSelector":
    case "XMLFilterExpression":
    case "XML":
    case "XMLElement":
    case "XMLList":
    case "XMLEscape":
    case "XMLText":
    case "XMLStartTag":
    case "XMLEndTag":
    case "XMLPointTag":
    case "XMLName":
    case "XMLAttribute":
    case "XMLCdata":
    case "XMLComment":
    case "XMLProcessingInstruction":
    default:
      debugger;
      throw new Error("unknown type: " + JSON.stringify(n.type));
  }
  return p;
}

function printStatementSequence(path, options, print) {
  let printed = [];

  path.map(function(stmtPath, i) {
    var stmt = stmtPath.getValue();

    // Just in case the AST has been modified to contain falsy
    // "statements," it's safer simply to skip them.
    if (!stmt) {
      return;
    }

    // Skip printing EmptyStatement nodes to avoid leaving stray
    // semicolons lying around.
    if (stmt.type === "EmptyStatement") {
      return;
    }

    const stmtPrinted = print(stmtPath);
    const text = options.originalText;
    const parts = [];

    parts.push(stmtPrinted);

    if (
      util.newlineExistsAfter(text, util.locEnd(stmt)) &&
        !isLastStatement(stmtPath)
    ) {
      parts.push(hardline);
    }

    printed.push(concat(parts));
  });

  return join(hardline, printed);
}

function printPropertyKey(path, options, print) {
  var node = path.getNode().key;
  if (
    (node.type === "StringLiteral" ||
      node.type === "Literal" && typeof node.value === "string") &&
      isIdentifierName(node.value) &&
      // There's a bug in the flow parser where it throws if there are
      // unquoted unicode literals as keys. Let's quote them for now.
      (options.parser !== 'flow' || node.value.match(/[a-zA-Z0-9$_]/))
  ) {
    // 'a' -> a
    return node.value;
  }
  return path.call(print, "key");
}

function printMethod(path, options, print) {
  var node = path.getNode();
  var kind = node.kind;
  var parts = [];

  if (node.type === "ObjectMethod" || node.type === "ClassMethod") {
    node.value = node;
  } else {
    namedTypes.FunctionExpression.assert(node.value);
  }

  if (node.value.async) {
    parts.push("async ");
  }

  if (!kind || kind === "init" || kind === "method" || kind === "constructor") {
    if (node.value.generator) {
      parts.push("*");
    }
  } else {
    assert.ok(kind === "get" || kind === "set");

    parts.push(kind, " ");
  }

  var key = printPropertyKey(path, options, print);

  if (node.computed) {
    key = concat([ "[", key, "]" ]);
  }

  parts.push(
    key,
    path.call(print, "value", "typeParameters"),
    multilineGroup(
      concat([
        path.call(
          function(valuePath) {
            return printFunctionParams(valuePath, print, options);
          },
          "value"
        ),
        path.call(p => printReturnType(p, print), "value")
      ])
    ),
    " ",
    path.call(print, "value", "body")
  );

  return concat(parts);
}

function printArgumentsList(path, options, print) {
  var printed = path.map(print, "arguments");
  var args;

  if (printed.length === 0) {
    return "()";
  }

  const lastArg = util.getLast(path.getValue().arguments);
  // This is just an optimization; I think we could return the
  // conditional group for all function calls, but it's more expensive
  // so only do it for specific forms.
  const groupLastArg = lastArg.type === "ObjectExpression" ||
    lastArg.type === "ArrayExpression" ||
    lastArg.type === "FunctionExpression" ||
    lastArg.type === "ArrowFunctionExpression" &&
      (lastArg.body.type === "BlockStatement" ||
        lastArg.body.type === "ArrowFunctionExpression" ||
        lastArg.body.type === "ObjectExpression" ||
        lastArg.body.type === "ArrayExpression" ||
        lastArg.body.type === "JSXElement") ||
    lastArg.type === "NewExpression";

  if (groupLastArg) {
    const shouldBreak = printed.slice(0, -1).some(hasHardLine);
    return conditionalGroup(
      [
        concat([ "(", join(concat([ ", " ]), printed), ")" ]),
        concat([
          "(",
          join(concat([ ",", line ]), printed.slice(0, -1)),
          printed.length > 1 ? ", " : "",
          group(util.getLast(printed), { shouldBreak: true }),
          ")"
        ]),
        group(
          concat([
            "(",
            indent(
              options.tabWidth,
              concat([ line, join(concat([ ",", line ]), printed) ])
            ),
            options.trailingComma ? "," : "",
            line,
            ")"
          ]),
          { shouldBreak: true }
        )
      ],
      { shouldBreak }
    );
  }

  return multilineGroup(
    concat([
      "(",
      indent(
        options.tabWidth,
        concat([ softline, join(concat([ ",", line ]), printed) ])
      ),
      ifBreak(options.trailingComma ? "," : ""),
      softline,
      ")"
    ])
  );
}

function printFunctionParams(path, print, options) {
  var fun = path.getValue();
  // namedTypes.Function.assert(fun);
  var printed = path.map(print, "params");

  if (fun.defaults) {
    path.each(
      function(defExprPath) {
        var i = defExprPath.getName();
        var p = printed[i];

        if (p && defExprPath.getValue()) {
          printed[i] = concat([ p, " = ", print(defExprPath) ]);
        }
      },
      "defaults"
    );
  }

  if (fun.rest) {
    printed.push(concat([ "...", path.call(print, "rest") ]));
  }

  if (printed.length === 0) {
    return "()";
  }

  const lastParam = util.getLast(path.getValue().params);
  const canHaveTrailingComma = !(lastParam && lastParam.type === "RestElement") && !fun.rest;

  return concat([
    "(",
    indent(
      options.tabWidth,
      concat([ softline, join(concat([ ",", line ]), printed) ])
    ),
    ifBreak(canHaveTrailingComma && options.trailingComma ? "," : ""),
    softline,
    ")"
  ]);
}

function printObjectMethod(path, options, print) {
  var objMethod = path.getValue();
  var parts = [];

  if (objMethod.async) parts.push("async ");

  if (objMethod.generator) parts.push("*");

  if (
    objMethod.method || objMethod.kind === "get" || objMethod.kind === "set"
  ) {
    return printMethod(path, options, print);
  }

  var key = printPropertyKey(path, options, print);

  if (objMethod.computed) {
    parts.push("[", key, "]");
  } else {
    parts.push(key);
  }

  if (objMethod.typeParameters) {
    parts.push(path.call(print, "typeParameters"));
  }

  parts.push(
    multilineGroup(
      concat([
        printFunctionParams(path, print, options),
        printReturnType(path, print)
      ])
    ),
    " ",
    path.call(print, "body")
  );

  return concat(parts);
}

function printReturnType(path, print) {
  const n = path.getValue();
  const parts = [ path.call(print, "returnType") ];

  if (n.predicate) {
    // The return type will already add the colon, but otherwise we
    // need to do it ourselves
    parts.push(n.returnType ? " " : ": ", path.call(print, "predicate"));
  }

  return concat(parts);
}

function typeIsFunction(type) {
  return type === "FunctionExpression" ||
    type === "ArrowFunctionExpression" ||
    type === "NewExpression";
}

function printExportDeclaration(path, options, print) {
  var decl = path.getValue();
  var parts = [ "export " ];

  namedTypes.Declaration.assert(decl);

  if (decl["default"] || decl.type === "ExportDefaultDeclaration") {
    parts.push("default ");
  }

  if (decl.declaration) {
    parts.push(path.call(print, "declaration"));

    if (
      decl.type === "ExportDefaultDeclaration" &&
        (decl.declaration.type !== "ClassDeclaration" &&
          decl.declaration.type !== "FunctionDeclaration" &&
          decl.declaration.type !== "FunctionExpression")
    ) {
      parts.push(";");
    }
  } else {
    if (decl.specifiers && decl.specifiers.length > 0) {
      if (
        decl.specifiers.length === 1 &&
          decl.specifiers[0].type === "ExportBatchSpecifier"
      ) {
        parts.push("*");
      } else {
        parts.push(
          decl.exportKind === "type" ? "type " : "",
          multilineGroup(
            concat([
              "{",
              indent(
                options.tabWidth,
                concat([
                  options.bracketSpacing ? line : softline,
                  join(concat([ ",", line ]), path.map(print, "specifiers"))
                ])
              ),
              ifBreak(options.trailingComma ? "," : ""),
              options.bracketSpacing ? line : softline,
              "}"
            ])
          )
        );
      }
    } else {
      parts.push("{}");
    }

    if (decl.source) {
      parts.push(" from ", path.call(print, "source"));
    }

    parts.push(";");
  }

  return concat(parts);
}

function printFlowDeclaration(path, parts) {
  var parentExportDecl = util.getParentExportDeclaration(path);

  if (parentExportDecl) {
    assert.strictEqual(parentExportDecl.type,