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Reference to the function expression identifier in it's body has different symbol #37131
Description
TypeScript Version: 3.8.2, 3.9.0-dev.20200229
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Code
const ts = require('typescript');
const content = 'const x = function y() { y }';
const host = ts.createCompilerHost({});
const originalReadFile = host.readFile;
host.readFile = fileName => (fileName === 'main.ts' ? content : originalReadFile(fileName));
const program = ts.createProgram({ host, rootNames: ['main.ts'], options: { types: [] } });
program.getSemanticDiagnostics();
const typeChecker = program.getDiagnosticsProducingTypeChecker();
const sourceFile = program.getSourceFile('main.ts');
const fn = sourceFile.statements[0].declarationList.declarations[0].initializer;
const y = fn.name;
const yInBody = fn.body.statements[0].expression.expression;
const ySymbol = typeChecker.getSymbolAtLocation(y);
const yInBodySymbol = typeChecker.getSymbolAtLocation(yInBody);
console.log(ySymbol === yInBodySymbol);Expected behavior:
y identifier in function name and y reference in it's body to have the same symbol
Actual behavior:
They have different symbols.
Few notes:
- It wasn't the case in 3.7.5
- It's not the case when
program.getSemanticDiagnostics()is not called or a non-diagnostics-producing type checker is used (ref getTypeChecker returns the same checker manufactured for diagnostics … #28584) - It happens only with function expression, i.e.
const content = 'function y() { y }'works as expected
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Activity
RyanCavanaugh commentedon Mar 4, 2020
This is sort of a bug and sort of not -- in this particular case we (probably?) don't need two different symbols. However, symbol identity is not an invariant of the API contract and you should use different means (e.g. checking
declarations) to determine if two instances of the same identifier mean the "same" thing depending on your particular definition of sameness. The TS language service API provides functionality for "find all references" that handles most of this for you depending on your requirements.RyanCavanaugh commentedon Sep 4, 2026
Symbolobject identity is not a guaranteed Compiler API contract, including for the function-expression name and its reference after diagnostics have been requested. Use the declarations associated with each symbol when comparing their meanings, or use the language service find-references API for reference queries.The JavaScript Compiler API from TypeScript 6 and earlier is no longer being developed; it has been superseded by the TypeScript 7 API.