Key Concepts and Artifacts

Relevant source files

• src/compiler/binder.ts
• src/compiler/checker.ts
• src/compiler/commandLineParser.ts
• src/compiler/core.ts
• src/compiler/diagnosticMessages.json
• src/compiler/emitter.ts
• src/compiler/moduleNameResolver.ts
• src/compiler/moduleSpecifiers.ts
• src/compiler/parser.ts
• src/compiler/program.ts
• src/compiler/resolutionCache.ts
• src/compiler/scanner.ts
• src/compiler/sys.ts
• src/compiler/types.ts
• src/compiler/utilities.ts
• src/harness/client.ts
• src/harness/fourslashImpl.ts
• src/harness/fourslashInterfaceImpl.ts
• src/harness/harnessLanguageService.ts
• src/harness/vfsUtil.ts
• src/lib/es2015.collection.d.ts
• src/lib/es2015.core.d.ts
• src/lib/es2015.iterable.d.ts
• src/lib/es2015.proxy.d.ts
• src/lib/es2015.reflect.d.ts
• src/lib/es2015.symbol.d.ts
• src/lib/es2015.symbol.wellknown.d.ts
• src/lib/es2019.d.ts
• src/lib/es2020.bigint.d.ts
• src/lib/es5.d.ts
• src/server/editorServices.ts
• src/server/project.ts
• src/server/protocol.ts
• src/server/scriptInfo.ts
• src/server/scriptVersionCache.ts
• src/server/session.ts
• src/server/utilities.ts
• src/services/codefixes/importFixes.ts
• src/services/completions.ts
• src/services/exportInfoMap.ts
• src/services/findAllReferences.ts
• src/services/goToDefinition.ts
• src/services/importTracker.ts
• src/services/services.ts
• src/services/types.ts
• src/services/utilities.ts
• src/testRunner/unittests/tsserver/exportMapCache.ts
• tests/baselines/reference/APISample_compile.js
• tests/baselines/reference/APISample_linter.js
• tests/baselines/reference/APISample_transform.js
• tests/baselines/reference/APISample_watcher.js
• tests/baselines/reference/api/typescript.d.ts
• tests/baselines/reference/bigintIndex.errors.txt
• tests/baselines/reference/bigintIndex.js
• tests/baselines/reference/bigintIndex.symbols
• tests/baselines/reference/bigintIndex.types
• tests/baselines/reference/bigintWithLib.errors.txt
• tests/baselines/reference/bigintWithLib.js
• tests/baselines/reference/bigintWithLib.symbols
• tests/baselines/reference/bigintWithLib.types
• tests/baselines/reference/completionsStringMethods.baseline
• tests/baselines/reference/dissallowSymbolAsWeakType.errors.txt
• tests/baselines/reference/extendingCollectionsWithCheckJs.symbols
• tests/baselines/reference/extendingCollectionsWithCheckJs.types
• tests/baselines/reference/mapConstructorOnReadonlyTuple.js
• tests/baselines/reference/mapConstructorOnReadonlyTuple.symbols
• tests/baselines/reference/mapConstructorOnReadonlyTuple.types
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.errors.txt
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.js
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.symbols
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty.types
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.js
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.symbols
• tests/baselines/reference/mappedTypeWithAsClauseAndLateBoundProperty2.types
• tests/baselines/reference/modularizeLibrary_UsingES5LibAndES6FeatureLibs.types
• tests/baselines/reference/newMap.errors.txt
• tests/baselines/reference/newMap.js
• tests/baselines/reference/newMap.symbols
• tests/baselines/reference/newMap.types
• tests/baselines/reference/tsbuild/outFile/rebuilds-completely-when-command-line-incremental-flag-changes-between-non-dts-changes.js
• tests/baselines/reference/tsbuild/outFile/when-final-project-is-not-composite-but-uses-project-references.js
• tests/baselines/reference/tsserver/exportMapCache/invalidates-the-cache-when-a-file-is-opened-with-different-contents.js
• tests/cases/compiler/bigintIndex.ts
• tests/cases/compiler/bigintWithLib.ts
• tests/cases/compiler/bigintWithoutLib.ts
• tests/cases/compiler/extendingCollectionsWithCheckJs.ts
• tests/cases/compiler/mapConstructorOnReadonlyTuple.ts
• tests/cases/compiler/mappedTypeWithAsClauseAndLateBoundProperty.ts
• tests/cases/compiler/mappedTypeWithAsClauseAndLateBoundProperty2.ts
• tests/cases/compiler/newMap.ts
• tests/cases/compiler/typedArrayConstructorOverloads.ts
• tests/cases/fourslash/fourslash.ts
• tests/cases/fourslash/server/completionsOverridingMethodCrash2.ts

This page defines the core technical artifacts and conceptual entities used throughout the TypeScript codebase. Understanding these artifacts is essential for navigating the compiler, language service, and server implementations.

Core Compiler Artifacts

The compiler operates on a set of fundamental data structures that represent the code, its semantic meaning, and the overall compilation context.

SourceFile and AST (Abstract Syntax Tree)

A SourceFile is the top-level representation of a single TypeScript or JavaScript file src/compiler/types.ts3843-3889 It contains the full source text and a tree of Node objects src/compiler/types.ts747-814

• SyntaxKind: Every node in the AST has a kind property of type SyntaxKind, which identifies the grammatical construct (e.g., IfStatement, Identifier) src/compiler/types.ts40-455
• TextRange: Nodes track their position in the original source via pos (start including trivia) and end src/compiler/types.ts28-31

Symbol, Type, and Signature

These objects represent the semantic "meaning" of the code after the binder and type checker have processed the AST.

• Symbol: Links a declaration in the AST to a unique identity across the program. Multiple declarations (like a namespace and a function with the same name) can merge into a single Symbol src/compiler/types.ts4460-4493
• Type: Represents the static type of an expression or symbol (e.g., NumberType, UnionType, InterfaceType) src/compiler/types.ts4549-4628
• Signature: Specifically represents the call, construct, or index signatures of a type src/compiler/types.ts4503-4528

Program

The Program is the central coordinator of a compilation session src/compiler/types.ts4051-4156 It holds the set of SourceFiles, the CompilerOptions, and provides access to the TypeChecker src/compiler/program.ts50-51

Artifact Association: Code to Entities

The following diagram illustrates how raw code maps to internal compiler artifacts.

Code to Entity Mapping

Sources: src/compiler/types.ts747-814 src/compiler/types.ts3843-3889 src/compiler/types.ts4460-4493 src/compiler/types.ts4549-4628

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Diagnostics and Baselines

Diagnostics

Diagnostics are the errors, warnings, and suggestions produced by the compiler src/compiler/types.ts4214-4241

• Structure: Each diagnostic has a code (e.g., 1002 for "Unterminated string literal"), a category, and a messageText src/compiler/diagnosticMessages.json2-5
• Location: DiagnosticWithLocation includes a file, start, and length to point exactly where the issue occurs src/compiler/types.ts4234-4241

Baselines

Baselines are reference files used for regression testing. They live in tests/baselines/reference/.

• Compiler Baselines: Compare the generated .js, .d.ts, and errors against known good versions tests/baselines/reference/APISample_compile.js1-5
• Fourslash Baselines: Capture IDE behavior like completion lists or quick info tests/baselines/reference/completionsStringMethods.baseline1-10

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Infrastructure Artifacts (LKG and tsserver)

LKG (Last Known Good)

The lib/ directory contains the "Last Known Good" version of the compiler. Because the TypeScript compiler is written in TypeScript, it requires a pre-compiled version of itself to build the current source code (bootstrapping).

Language Service and tsserver

• LanguageService: An API that provides editor-like features (IntelliSense, Rename, Go-to-Definition) over a Program src/services/services.ts212-213
• tsserver: A standalone Node.js executable that wraps the LanguageService and communicates with editors via a JSON-RPC protocol src/server/protocol.ts49-126

System and Project Management

The compiler interacts with the environment through a System host and manages files via ScriptInfo.

System Architecture and Data Flow

Sources: src/server/editorServices.ts182-195 src/server/project.ts1-10 src/server/scriptInfo.ts1-10

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Summary of Key Classes and Locations

Artifact	Primary Interface/Class	Primary Location
AST Node	Node	src/compiler/types.ts747
Source File	SourceFile	src/compiler/types.ts3843
Semantic Identity	Symbol	src/compiler/types.ts4460
Type System Entity	Type	src/compiler/types.ts4549
Compilation Unit	Program	src/compiler/program.ts50
Error Reporting	Diagnostic	src/compiler/types.ts4214
Language Server	Session	src/server/session.ts1-10
Editor Logic	LanguageService	src/services/services.ts212

Sources: src/compiler/types.ts1-200 src/compiler/program.ts1-50 src/services/services.ts1-250