visitor.js

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */

// @flow

import isEmpty from "lodash/isEmpty";
import type { SourceId, SourceLocation } from "../../../types";
import * as t from "@babel/types";
import type {
  Node,
  TraversalAncestors,
  Location as BabelLocation
} from "@babel/types";

import getFunctionName from "../utils/getFunctionName";
import { getAst } from "../utils/ast";

/**
 * "implicit"
 * Variables added automaticly like "this" and "arguments"
 *
 * "var"
 * Variables declared with "var" or non-block function declarations
 *
 * "let"
 * Variables declared with "let".
 *
 * "const"
 * Variables declared with "const", or added as const
 * bindings like inner function expressions and inner class names.
 *
 * "import"
 * Imported binding names exposed from other modules.
 *
 * "global"
 * Variables that reference undeclared global values.
 */
export type BindingType =
  | "implicit"
  | "var"
  | "const"
  | "let"
  | "import"
  | "global";

export type BindingLocationType = "ref" | BindingDeclarationType;
export type BindingDeclarationType =
  | "fn-expr"
  | "fn-decl"
  | "fn-param"
  | "class-decl"
  | "class-inner"
  | "import-decl"
  | "import-ns-decl"
  | "ts-enum-decl"
  | "ts-namespace-decl"
  | "var"
  | "let"
  | "const"
  | "catch";

export type BindingLocation = BindingDeclarationLocation | BindingRefLocation;

export type BindingRefLocation = {
  type: "ref",
  start: SourceLocation,
  end: SourceLocation,
  meta?: BindingMetaValue | null
};
export type BindingDeclarationLocation = {
  type: BindingDeclarationType,

  start: SourceLocation,
  end: SourceLocation,

  // The overall location of the declaration that this binding is part of.
  declaration: {
    start: SourceLocation,
    end: SourceLocation
  },

  // If this declaration was an import, include the name of the imported
  // binding that this binding references.
  importName?: string
};
export type BindingData = {
  type: BindingType,
  refs: Array<BindingLocation>
};

// Location information about the expression immediartely surrounding a
// given binding reference.
export type BindingMetaValue =
  | {
      type: "inherit",
      start: SourceLocation,
      end: SourceLocation,
      parent: BindingMetaValue | null
    }
  | {
      type: "call",
      start: SourceLocation,
      end: SourceLocation,
      parent: BindingMetaValue | null
    }
  | {
      type: "member",
      start: SourceLocation,
      end: SourceLocation,
      property: string,
      parent: BindingMetaValue | null
    };

export type ScopeBindingList = {
  [name: string]: BindingData
};

export type SourceScope = {
  type: "object" | "function" | "block",
  displayName: string,
  start: SourceLocation,
  end: SourceLocation,
  bindings: ScopeBindingList
};

export type ParsedScope = SourceScope & {
  children: ?(ParsedScope[])
};

export type ParseJSScopeVisitor = {
  traverseVisitor: any,
  toParsedScopes: () => ParsedScope[]
};

type TempScope = {
  type: "object" | "function" | "function-body" | "block" | "module",
  displayName: string,
  parent: TempScope | null,
  children: Array<TempScope>,
  loc: BabelLocation,
  bindings: ScopeBindingList
};

type ScopeCollectionVisitorState = {
  sourceId: SourceId,
  inType: Node | null,
  freeVariables: Map<string, Array<BindingLocation>>,
  freeVariableStack: Array<Map<string, Array<BindingLocation>>>,
  scope: TempScope,
  scopeStack: Array<TempScope>,
  declarationBindingIds: Set<Node>
};

function isGeneratedId(id: string) {
  return !/\/originalSource/.test(id);
}

export function parseSourceScopes(sourceId: SourceId): ?Array<ParsedScope> {
  const ast = getAst(sourceId);
  if (isEmpty(ast)) {
    return null;
  }

  return buildScopeList(ast, sourceId);
}

export function buildScopeList(ast: Node, sourceId: SourceId) {
  const { global, lexical } = createGlobalScope(ast, sourceId);

  const state = {
    sourceId,
    freeVariables: new Map(),
    freeVariableStack: [],
    inType: null,
    scope: lexical,
    scopeStack: [],
    declarationBindingIds: new Set()
  };
  t.traverse(ast, scopeCollectionVisitor, state);

  for (const [key, freeVariables] of state.freeVariables) {
    let binding = global.bindings[key];
    if (!binding) {
      binding = {
        type: "global",
        refs: []
      };
      global.bindings[key] = binding;
    }

    binding.refs = freeVariables.concat(binding.refs);
  }

  // TODO: This should probably check for ".mjs" extension on the
  // original file, and should also be skipped if the the generated
  // code is an ES6 module rather than a script.
  if (
    isGeneratedId(sourceId) ||
    ((ast: any).program.sourceType === "script" && !looksLikeCommonJS(global))
  ) {
    stripModuleScope(global);
  }

  return toParsedScopes([global], sourceId) || [];
}

function toParsedScopes(
  children: TempScope[],
  sourceId: SourceId
): ?(ParsedScope[]) {
  if (!children || children.length === 0) {
    return undefined;
  }
  return children.map(scope => {
    // Removing unneed information from TempScope such as parent reference.
    // We also need to convert BabelLocation to the Location type.
    return {
      start: scope.loc.start,
      end: scope.loc.end,
      type:
        scope.type === "module" || scope.type === "function-body"
          ? "block"
          : scope.type,
      displayName: scope.displayName,
      bindings: scope.bindings,
      children: toParsedScopes(scope.children, sourceId)
    };
  });
}

function createTempScope(
  type: "object" | "function" | "function-body" | "block" | "module",
  displayName: string,
  parent: TempScope | null,
  loc: {
    start: SourceLocation,
    end: SourceLocation
  }
): TempScope {
  const result = {
    type,
    displayName,
    parent,
    children: [],
    loc,
    bindings: (Object.create(null): any)
  };
  if (parent) {
    parent.children.push(result);
  }
  return result;
}
function pushTempScope(
  state: ScopeCollectionVisitorState,
  type: "object" | "function" | "function-body" | "block" | "module",
  displayName: string,
  loc: {
    start: SourceLocation,
    end: SourceLocation
  }
): TempScope {
  const scope = createTempScope(type, displayName, state.scope, loc);

  state.scope = scope;

  state.freeVariableStack.push(state.freeVariables);
  state.freeVariables = new Map();
  return scope;
}

function isNode(node?: Node, type: string): boolean {
  return node ? node.type === type : false;
}

function getVarScope(scope: TempScope): TempScope {
  let s = scope;
  while (s.type !== "function" && s.type !== "module") {
    if (!s.parent) {
      return s;
    }
    s = s.parent;
  }
  return s;
}

function fromBabelLocation(
  location: BabelLocation,
  sourceId: SourceId
): SourceLocation {
  return {
    sourceId,
    line: location.line,
    column: location.column
  };
}

function parseDeclarator(
  declaratorId: Node,
  targetScope: TempScope,
  type: BindingType,
  locationType: BindingDeclarationType,
  declaration: Node,
  state: ScopeCollectionVisitorState
) {
  if (isNode(declaratorId, "Identifier")) {
    let existing = targetScope.bindings[declaratorId.name];
    if (!existing) {
      existing = {
        type,
        refs: []
      };
      targetScope.bindings[declaratorId.name] = existing;
    }
    state.declarationBindingIds.add(declaratorId);
    existing.refs.push({
      type: locationType,
      start: fromBabelLocation(declaratorId.loc.start, state.sourceId),
      end: fromBabelLocation(declaratorId.loc.end, state.sourceId),
      declaration: {
        start: fromBabelLocation(declaration.loc.start, state.sourceId),
        end: fromBabelLocation(declaration.loc.end, state.sourceId)
      }
    });
  } else if (isNode(declaratorId, "ObjectPattern")) {
    declaratorId.properties.forEach(prop => {
      parseDeclarator(
        prop.value,
        targetScope,
        type,
        locationType,
        declaration,
        state
      );
    });
  } else if (isNode(declaratorId, "ArrayPattern")) {
    declaratorId.elements.forEach(item => {
      parseDeclarator(
        item,
        targetScope,
        type,
        locationType,
        declaration,
        state
      );
    });
  } else if (isNode(declaratorId, "AssignmentPattern")) {
    parseDeclarator(
      declaratorId.left,
      targetScope,
      type,
      locationType,
      declaration,
      state
    );
  } else if (isNode(declaratorId, "RestElement")) {
    parseDeclarator(
      declaratorId.argument,
      targetScope,
      type,
      locationType,
      declaration,
      state
    );
  } else if (t.isTSParameterProperty(declaratorId)) {
    parseDeclarator(
      declaratorId.parameter,
      targetScope,
      type,
      locationType,
      declaration,
      state
    );
  }
}

function isLetOrConst(node) {
  return node.kind === "let" || node.kind === "const";
}

function hasLexicalDeclaration(node, parent) {
  const nodes = [];
  if (t.isSwitchStatement(node)) {
    for (const caseNode of node.cases) {
      nodes.push(...caseNode.consequent);
    }
  } else {
    nodes.push(...node.body);
  }

  const isFunctionBody = t.isFunction(parent, { body: node });

  return nodes.some(
    child =>
      isLexicalVariable(child) ||
      t.isClassDeclaration(child) ||
      (!isFunctionBody && t.isFunctionDeclaration(child))
  );
}
function isLexicalVariable(node) {
  return isNode(node, "VariableDeclaration") && isLetOrConst(node);
}

function createGlobalScope(
  ast: Node,
  sourceId: SourceId
): { global: TempScope, lexical: TempScope } {
  const global = createTempScope("object", "Global", null, {
    start: fromBabelLocation(ast.loc.start, sourceId),
    end: fromBabelLocation(ast.loc.end, sourceId)
  });

  const lexical = createTempScope("block", "Lexical Global", global, {
    start: fromBabelLocation(ast.loc.start, sourceId),
    end: fromBabelLocation(ast.loc.end, sourceId)
  });

  return {
    global,
    lexical
  };
}

const scopeCollectionVisitor = {
  // eslint-disable-next-line complexity
  enter(
    node: Node,
    ancestors: TraversalAncestors,
    state: ScopeCollectionVisitorState
  ) {
    state.scopeStack.push(state.scope);

    const parentNode =
      ancestors.length === 0 ? null : ancestors[ancestors.length - 1].node;

    if (state.inType) {
      return;
    }

    if (t.isProgram(node)) {
      const scope = pushTempScope(state, "module", "Module", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
      scope.bindings.this = {
        type: "implicit",
        refs: []
      };
    } else if (t.isFunction(node)) {
      let scope = state.scope;
      if (t.isFunctionExpression(node) && isNode(node.id, "Identifier")) {
        scope = pushTempScope(state, "block", "Function Expression", {
          start: fromBabelLocation(node.loc.start, state.sourceId),
          end: fromBabelLocation(node.loc.end, state.sourceId)
        });
        state.declarationBindingIds.add(node.id);
        scope.bindings[node.id.name] = {
          type: "const",
          refs: [
            {
              type: "fn-expr",
              start: fromBabelLocation(node.id.loc.start, state.sourceId),
              end: fromBabelLocation(node.id.loc.end, state.sourceId),
              declaration: {
                start: fromBabelLocation(node.loc.start, state.sourceId),
                end: fromBabelLocation(node.loc.end, state.sourceId)
              }
            }
          ]
        };
      }

      if (t.isFunctionDeclaration(node) && isNode(node.id, "Identifier")) {
        // This ignores Annex B function declaration hoisting, which
        // is probably a fine assumption.
        state.declarationBindingIds.add(node.id);
        const refs = [
          {
            type: "fn-decl",
            start: fromBabelLocation(node.id.loc.start, state.sourceId),
            end: fromBabelLocation(node.id.loc.end, state.sourceId),
            declaration: {
              start: fromBabelLocation(node.loc.start, state.sourceId),
              end: fromBabelLocation(node.loc.end, state.sourceId)
            }
          }
        ];

        if (scope.type === "block") {
          scope.bindings[node.id.name] = {
            type: "let",
            refs
          };
        } else {
          getVarScope(scope).bindings[node.id.name] = {
            type: "var",
            refs
          };
        }
      }

      scope = pushTempScope(
        state,
        "function",
        getFunctionName(node, parentNode),
        {
          // Being at the start of a function doesn't count as
          // being inside of it.
          start: fromBabelLocation(
            node.params[0] ? node.params[0].loc.start : node.loc.start,
            state.sourceId
          ),
          end: fromBabelLocation(node.loc.end, state.sourceId)
        }
      );

      node.params.forEach(param =>
        parseDeclarator(param, scope, "var", "fn-param", node, state)
      );

      if (!t.isArrowFunctionExpression(node)) {
        scope.bindings.this = {
          type: "implicit",
          refs: []
        };
        scope.bindings.arguments = {
          type: "implicit",
          refs: []
        };
      }

      if (
        t.isBlockStatement(node.body) &&
        hasLexicalDeclaration(node.body, node)
      ) {
        scope = pushTempScope(state, "function-body", "Function Body", {
          start: fromBabelLocation(node.body.loc.start, state.sourceId),
          end: fromBabelLocation(node.body.loc.end, state.sourceId)
        });
      }
    } else if (t.isClass(node)) {
      if (t.isIdentifier(node.id)) {
        // For decorated classes, the AST considers the first the decorator
        // to be the start of the class. For the purposes of mapping class
        // declarations however, we really want to look for the "class Foo"
        // piece. To achieve that, we estimate the location of the declaration
        // instead.
        let declStart = node.loc.start;
        if (node.decorators && node.decorators.length > 0) {
          // Estimate the location of the "class" keyword since it
          // is unlikely to be a different line than the class name.
          declStart = {
            line: node.id.loc.start.line,
            column: node.id.loc.start.column - "class ".length
          };
        }

        const declaration = {
          start: fromBabelLocation(declStart, state.sourceId),
          end: fromBabelLocation(node.loc.end, state.sourceId)
        };

        if (t.isClassDeclaration(node)) {
          state.declarationBindingIds.add(node.id);
          state.scope.bindings[node.id.name] = {
            type: "let",
            refs: [
              {
                type: "class-decl",
                start: fromBabelLocation(node.id.loc.start, state.sourceId),
                end: fromBabelLocation(node.id.loc.end, state.sourceId),
                declaration
              }
            ]
          };
        }

        const scope = pushTempScope(state, "block", "Class", {
          start: fromBabelLocation(node.loc.start, state.sourceId),
          end: fromBabelLocation(node.loc.end, state.sourceId)
        });

        state.declarationBindingIds.add(node.id);
        scope.bindings[node.id.name] = {
          type: "const",
          refs: [
            {
              type: "class-inner",
              start: fromBabelLocation(node.id.loc.start, state.sourceId),
              end: fromBabelLocation(node.id.loc.end, state.sourceId),
              declaration
            }
          ]
        };
      }
    } else if (t.isForXStatement(node) || t.isForStatement(node)) {
      const init = node.init || node.left;
      if (isNode(init, "VariableDeclaration") && isLetOrConst(init)) {
        // Debugger will create new lexical environment for the for.
        pushTempScope(state, "block", "For", {
          // Being at the start of a for loop doesn't count as
          // being inside it.
          start: fromBabelLocation(init.loc.start, state.sourceId),
          end: fromBabelLocation(node.loc.end, state.sourceId)
        });
      }
    } else if (t.isCatchClause(node)) {
      const scope = pushTempScope(state, "block", "Catch", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
      parseDeclarator(node.param, scope, "var", "catch", node, state);
    } else if (
      t.isBlockStatement(node) &&
      // Function body's are handled in the function logic above.
      !t.isFunction(parentNode) &&
      hasLexicalDeclaration(node, parentNode)
    ) {
      // Debugger will create new lexical environment for the block.
      pushTempScope(state, "block", "Block", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
    } else if (
      t.isVariableDeclaration(node) &&
      (node.kind === "var" ||
        // Lexical declarations in for statements are handled above.
        !t.isForStatement(parentNode, { init: node }) ||
        !t.isForXStatement(parentNode, { left: node }))
    ) {
      // Finds right lexical environment
      const hoistAt = !isLetOrConst(node)
        ? getVarScope(state.scope)
        : state.scope;
      node.declarations.forEach(declarator => {
        parseDeclarator(
          declarator.id,
          hoistAt,
          node.kind,
          node.kind,
          node,
          state
        );
      });
    } else if (
      t.isImportDeclaration(node) &&
      (!node.importKind || node.importKind === "value")
    ) {
      node.specifiers.forEach(spec => {
        if (spec.importKind && spec.importKind !== "value") {
          return;
        }

        if (t.isImportNamespaceSpecifier(spec)) {
          state.declarationBindingIds.add(spec.local);

          state.scope.bindings[spec.local.name] = {
            // Imported namespaces aren't live import bindings, they are
            // just normal const bindings.
            type: "const",
            refs: [
              {
                type: "import-ns-decl",
                start: fromBabelLocation(spec.local.loc.start, state.sourceId),
                end: fromBabelLocation(spec.local.loc.end, state.sourceId),
                declaration: {
                  start: fromBabelLocation(node.loc.start, state.sourceId),
                  end: fromBabelLocation(node.loc.end, state.sourceId)
                }
              }
            ]
          };
        } else {
          state.declarationBindingIds.add(spec.local);

          state.scope.bindings[spec.local.name] = {
            type: "import",
            refs: [
              {
                type: "import-decl",
                start: fromBabelLocation(spec.local.loc.start, state.sourceId),
                end: fromBabelLocation(spec.local.loc.end, state.sourceId),
                importName: t.isImportDefaultSpecifier(spec)
                  ? "default"
                  : spec.imported.name,
                declaration: {
                  start: fromBabelLocation(node.loc.start, state.sourceId),
                  end: fromBabelLocation(node.loc.end, state.sourceId)
                }
              }
            ]
          };
        }
      });
    } else if (t.isTSEnumDeclaration(node)) {
      state.declarationBindingIds.add(node.id);
      state.scope.bindings[node.id.name] = {
        type: "const",
        refs: [
          {
            type: "ts-enum-decl",
            start: fromBabelLocation(node.id.loc.start, state.sourceId),
            end: fromBabelLocation(node.id.loc.end, state.sourceId),
            declaration: {
              start: fromBabelLocation(node.loc.start, state.sourceId),
              end: fromBabelLocation(node.loc.end, state.sourceId)
            }
          }
        ]
      };
    } else if (t.isTSModuleDeclaration(node)) {
      state.declarationBindingIds.add(node.id);
      state.scope.bindings[node.id.name] = {
        type: "const",
        refs: [
          {
            type: "ts-namespace-decl",
            start: fromBabelLocation(node.id.loc.start, state.sourceId),
            end: fromBabelLocation(node.id.loc.end, state.sourceId),
            declaration: {
              start: fromBabelLocation(node.loc.start, state.sourceId),
              end: fromBabelLocation(node.loc.end, state.sourceId)
            }
          }
        ]
      };
    } else if (t.isTSModuleBlock(node)) {
      pushTempScope(state, "block", "TypeScript Namespace", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
    } else if (
      t.isIdentifier(node) &&
      t.isReferenced(node, parentNode) &&
      // Babel doesn't cover this in 'isReferenced' yet, but it should
      // eventually.
      !t.isTSEnumMember(parentNode, { id: node }) &&
      !t.isTSModuleDeclaration(parentNode, { id: node }) &&
      // isReferenced above fails to see `var { foo } = ...` as a non-reference
      // because the direct parent is not enough to know that the pattern is
      // used within a variable declaration.
      !state.declarationBindingIds.has(node)
    ) {
      let freeVariables = state.freeVariables.get(node.name);
      if (!freeVariables) {
        freeVariables = [];
        state.freeVariables.set(node.name, freeVariables);
      }

      freeVariables.push({
        type: "ref",
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId),
        meta: buildMetaBindings(state.sourceId, node, ancestors)
      });
    } else if (isOpeningJSXIdentifier(node, ancestors)) {
      let freeVariables = state.freeVariables.get(node.name);
      if (!freeVariables) {
        freeVariables = [];
        state.freeVariables.set(node.name, freeVariables);
      }

      freeVariables.push({
        type: "ref",
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId),
        meta: buildMetaBindings(state.sourceId, node, ancestors)
      });
    } else if (t.isThisExpression(node)) {
      let freeVariables = state.freeVariables.get("this");
      if (!freeVariables) {
        freeVariables = [];
        state.freeVariables.set("this", freeVariables);
      }

      freeVariables.push({
        type: "ref",
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId),
        meta: buildMetaBindings(state.sourceId, node, ancestors)
      });
    } else if (t.isClassProperty(parentNode, { value: node })) {
      const scope = pushTempScope(state, "function", "Class Field", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
      scope.bindings.this = {
        type: "implicit",
        refs: []
      };
      scope.bindings.arguments = {
        type: "implicit",
        refs: []
      };
    } else if (
      t.isSwitchStatement(node) &&
      hasLexicalDeclaration(node, parentNode)
    ) {
      pushTempScope(state, "block", "Switch", {
        start: fromBabelLocation(node.loc.start, state.sourceId),
        end: fromBabelLocation(node.loc.end, state.sourceId)
      });
    }

    if (
      // In general Flow expressions are deleted, so they can't contain
      // runtime bindings, but typecasts are the one exception there.
      (t.isFlow(node) && !t.isTypeCastExpression(node)) ||
      // In general TS items are deleted, but TS has a few wrapper node
      // types that can contain general JS expressions.
      (node.type.startsWith("TS") &&
        !t.isTSTypeAssertion(node) &&
        !t.isTSAsExpression(node) &&
        !t.isTSNonNullExpression(node) &&
        !t.isTSModuleDeclaration(node) &&
        !t.isTSModuleBlock(node) &&
        !t.isTSParameterProperty(node) &&
        !t.isTSExportAssignment(node))
    ) {
      // Flag this node as a root "type" node. All items inside of this
      // will be skipped entirely.
      state.inType = node;
    }
  },
  exit(
    node: Node,
    ancestors: TraversalAncestors,
    state: ScopeCollectionVisitorState
  ) {
    const currentScope = state.scope;
    const parentScope = state.scopeStack.pop();
    if (!parentScope) {
      throw new Error("Assertion failure - unsynchronized pop");
    }
    state.scope = parentScope;

    // It is possible, as in the case of function expressions, that a single
    // node has added multiple scopes, so we need to traverse upward here
    // rather than jumping stright to 'parentScope'.
    for (
      let scope = currentScope;
      scope && scope !== parentScope;
      scope = scope.parent
    ) {
      const freeVariables = state.freeVariables;
      state.freeVariables = state.freeVariableStack.pop();
      const parentFreeVariables = state.freeVariables;

      // Match up any free variables that match this scope's bindings and
      // merge then into the refs.
      for (const key of Object.keys(scope.bindings)) {
        const binding = scope.bindings[key];

        const freeVars = freeVariables.get(key);
        if (freeVars) {
          binding.refs.push(...freeVars);
          freeVariables.delete(key);
        }
      }

      // Move any undeclared references in this scope into the parent for
      // processing in higher scopes.
      for (const [key, value] of freeVariables) {
        let refs = parentFreeVariables.get(key);
        if (!refs) {
          refs = [];
          parentFreeVariables.set(key, refs);
        }

        refs.push(...value);
      }
    }

    if (state.inType === node) {
      state.inType = null;
    }
  }
};

function isOpeningJSXIdentifier(
  node: Node,
  ancestors: TraversalAncestors
): boolean {
  if (!t.isJSXIdentifier(node)) {
    return false;
  }

  for (let i = ancestors.length - 1; i >= 0; i--) {
    const { node: parent, key } = ancestors[i];

    if (t.isJSXOpeningElement(parent) && key === "name") {
      return true;
    } else if (!t.isJSXMemberExpression(parent) || key !== "object") {
      break;
    }
  }

  return false;
}

function buildMetaBindings(
  sourceId: SourceId,
  node: Node,
  ancestors: TraversalAncestors,
  parentIndex: number = ancestors.length - 1
): BindingMetaValue | null {
  if (parentIndex <= 1) {
    return null;
  }
  const parent = ancestors[parentIndex].node;
  const grandparent = ancestors[parentIndex - 1].node;

  // Consider "0, foo" to be equivalent to "foo".
  if (
    t.isSequenceExpression(parent) &&
    parent.expressions.length === 2 &&
    t.isNumericLiteral(parent.expressions[0]) &&
    parent.expressions[1] === node
  ) {
    let start = parent.loc.start;
    let end = parent.loc.end;

    if (t.isCallExpression(grandparent, { callee: parent })) {
      // Attempt to expand the range around parentheses, e.g.
      // (0, foo.bar)()
      start = grandparent.loc.start;
      end = Object.assign({}, end);
      end.column += 1;
    }

    return {
      type: "inherit",
      start: fromBabelLocation(start, sourceId),
      end: fromBabelLocation(end, sourceId),
      parent: buildMetaBindings(sourceId, parent, ancestors, parentIndex - 1)
    };
  }

  // Consider "Object(foo)", and "__webpack_require__.i(foo)" to be
  // equivalent to "foo" since they are essentially identity functions.
  if (
    t.isCallExpression(parent) &&
    (t.isIdentifier(parent.callee, { name: "Object" }) ||
      (t.isMemberExpression(parent.callee, { computed: false }) &&
        t.isIdentifier(parent.callee.object, { name: "__webpack_require__" }) &&
        t.isIdentifier(parent.callee.property, { name: "i" }))) &&
    parent.arguments.length === 1 &&
    parent.arguments[0] === node
  ) {
    return {
      type: "inherit",
      start: fromBabelLocation(parent.loc.start, sourceId),
      end: fromBabelLocation(parent.loc.end, sourceId),
      parent: buildMetaBindings(sourceId, parent, ancestors, parentIndex - 1)
    };
  }

  if (t.isMemberExpression(parent, { object: node })) {
    if (parent.computed) {
      if (t.isStringLiteral(parent.property)) {
        return {
          type: "member",
          start: fromBabelLocation(parent.loc.start, sourceId),
          end: fromBabelLocation(parent.loc.end, sourceId),
          property: parent.property.value,
          parent: buildMetaBindings(
            sourceId,
            parent,
            ancestors,
            parentIndex - 1
          )
        };
      }
    } else {
      return {
        type: "member",
        start: fromBabelLocation(parent.loc.start, sourceId),
        end: fromBabelLocation(parent.loc.end, sourceId),
        property: parent.property.name,
        parent: buildMetaBindings(sourceId, parent, ancestors, parentIndex - 1)
      };
    }
  }
  if (
    t.isCallExpression(parent, { callee: node }) &&
    parent.arguments.length == 0
  ) {
    return {
      type: "call",
      start: fromBabelLocation(parent.loc.start, sourceId),
      end: fromBabelLocation(parent.loc.end, sourceId),
      parent: buildMetaBindings(sourceId, parent, ancestors, parentIndex - 1)
    };
  }

  return null;
}

function looksLikeCommonJS(rootScope: TempScope): boolean {
  const hasRefs = name =>