# Data flow — microsoft/TypeScript

> Canonical page: https://codevetter.com/unpack/typescript/data-flow

# Data flow — microsoft/TypeScript

Scanned commit 5f6db9c9148635b4cbf72f1193b821b9c6b42dcc (2026-09-22). Generated by codevetter codevetter 1.12.0 on 2026-09-22.

For the CLI, input is argv -> tsoptions parsing (with ancestor tsconfig discovery and extended-config caching) -> a file loader that walks imports/type directives as parse tasks -> parser.ParseSourceFile producing ast.SourceFile trees -> binder-produced symbols -> a parallel checker pool producing diagnostics -> transformer chain -> printer/sourcemap emit through vfs.FS.WriteFile. For the LSP/API servers the same core is wrapped by internal/project: an immutable Snapshot owns a SnapshotFS overlay plus a ProjectCollection, and every edit/request produces a new snapshot; language-service operations read a snapshot's program. The API server adds a registry layer assigning stable SymbolID/TypeID/NodeHandle values that are encoded to MessagePack or JSON for the Node client.
- CLI input boundary: execute.CommandLine lower-cases argv[0] to detect -b/--build, then tsoptions.ParseCommandLine/ParseBuildCommandLine produce ParsedCommandLine values; tscCompilation locates tsconfig.json by walking ancestor directories via tspath.ForEachAncestorDirectory. — [tsc/internal/execute/tsc.go#L53-64](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L53-L64) [tsc/internal/execute/tsc.go#L269-281](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L269-L281) [tsc/internal/tsoptions/commandlineparser.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/tsoptions/commandlineparser.go)
- tsconfig parsing (GetParsedCommandLineOfConfigFile) resolves `extends` chains through an ExtendedConfigCache, merges command-line compilerOptions wrapped under a 'compilerOptions' key, and reports config parse errors as diagnostics before any compilation. — [tsc/internal/execute/tsc.go#L200-226](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L200-L226) [tsc/internal/tsoptions/tsconfigparsing.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/tsoptions/tsconfigparsing.go) [tsc/internal/execute/tsc/extendedconfigcache.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/extendedconfigcache.go)
- File loading is a worklist of parseTask structs: each task loads a file via the compiler host, records module/type-reference resolutions in ModeAwareCache fields, and enqueues sub-tasks for discovered dependencies (filesparser.go/filesParser, fileloader.go). — [tsc/internal/compiler/filesparser.go#L17-55](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/filesparser.go#L17-L55) [tsc/internal/compiler/fileloader.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/fileloader.go) [tsc/internal/compiler/program.go#L289](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/program.go#L289)
- Module resolution is centralized in internal/module.Resolver with per-file mode-aware caches; resolved modules feed both the loader (which files to parse) and emit metadata (importHelpersImportSpecifier, jsxRuntimeImportSpecifier). — [tsc/internal/module/resolver.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/module/resolver.go) [tsc/internal/compiler/filesparser.go#L30-42](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/filesparser.go#L30-L42)
- Parse/bind/check/emit diagnostics flow through compiler.GetDiagnosticsOfAnyProgram; EmitFilesAndReportErrors calls GetBindDiagnostics and GetSemanticDiagnostics per file (timed against CompileTimes), then ProgramLike.Emit writes outputs via compiler.EmitOptions.WriteFile. — [tsc/internal/execute/tsc/emit.go#L74-140](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/emit.go#L74-L140) [tsc/internal/compiler/emitter.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/emitter.go)
- Emit runs a transformer chain (internal/transformers: tstransforms type erasure/legacy decorators/metadata, moduletransforms commonjs/esmodule, estransforms for downlevel ES features, declarations for .d.ts) feeding internal/printer and internal/sourcemap. — [tsc/internal/transformers/transformer.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/transformers/transformer.go) [tsc/internal/transformers/chain.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/transformers/chain.go) [tsc/internal/transformers/declarations/transform.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/transformers/declarations/transform.go) [tsc/internal/printer/printer.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/printer/printer.go)
- Type checking is parallelized by a CheckerPool on the Program (compilerCheckerPool enables grouped parallel iteration and non-exclusive access for emit); ProgramOptions.CreateCheckerPool is injectable so the project system can supply its own pool. — [tsc/internal/compiler/program.go#L84-91](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/program.go#L84-L91) [tsc/internal/compiler/checkerpool.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/checkerpool.go) [tsc/internal/project/checkerpool.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/project/checkerpool.go)
- In the language server, state ownership is an immutable project.Snapshot: it holds a SnapshotFS (overlay of open-file contents over the base FS), a ProjectCollection, ConfigFileRegistry, AutoImports registry, and user preferences; each update clones forward the unchanged state. — [tsc/internal/project/snapshot.go#L26-46](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/project/snapshot.go#L26-L46) [tsc/internal/project/snapshotfs.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/project/snapshotfs.go) [tsc/internal/project/projectcollection.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/project/projectcollection.go)
- LSP request path: stdin bytes -> lsproto.BaseReader -> json.Unmarshal into lsproto.Message -> dynamic_queue requestQueue -> handleRequestOrNotification -> handlers() lookup -> for document requests, session.GetLanguageService(ctx, uri) resolves the project/snapshot, then ls.LanguageService methods compute results converted by internal/ls/lsconv. — [tsc/internal/lsp/server.go#L133-140](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L133-L140) [tsc/internal/lsp/server.go#L1142-1192](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1142-L1192) [tsc/internal/lsp/server.go#L1341-1359](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1341-L1359) [tsc/internal/ls/lsconv/converters.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/ls/lsconv/converters.go)
- The API session assigns cross-process handles: symbols get IDs from a global atomic (ast.GetSymbolId) stored in a snapshot-wide symbolRegistry, while types and signatures get per-project registries keyed by project.ID to avoid ID collisions between checker pools. — [tsc/internal/api/session.go#L46-87](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/api/session.go#L46-L87)
- API transport: StdioServer.Run picks ipc.NewPipeTransport (PipePath) or NewStdioTransport, then wraps a session in either NewMessagePackProtocol+NewSyncConn or NewJSONRPCProtocol+NewAsyncConn depending on the --async flag. — [tsc/internal/api/server.go#L62-120](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/api/server.go#L62-L120) [tsc/internal/api/protocol_msgpack.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/api/protocol_msgpack.go) [tsc/internal/ipc/protocol_jsonrpc.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/ipc/protocol_jsonrpc.go)
- Node-side, the sync API client (packages/typescript/src/api/sync/client.ts) spawns the binary with getAPIProcessArgs, optionally enabling FS callbacks (--callbacks=...) so the Go server can call back into JS for readFile/fileExists/writeFile etc. via SyncRpcChannel. — [packages/typescript/src/api/sync/client.ts#L26-80](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/packages/typescript/src/api/sync/client.ts#L26-L80) [tsc/internal/api/callbackfs.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/api/callbackfs.go) [tsc/cmd/tsc/api.go#L30-34](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/api.go#L30-L34)
- Content-mapped files enter the pipeline when the host returns content-mapped source files (GetContentMappedSourceFiles); ReuseProgram must re-run the external transform for such files and falls back to a full rebuild on failure. — [tsc/internal/compiler/program.go#L334-349](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/program.go#L334-L349) [tsc/internal/contentmapper/hostimpl.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/contentmapper/hostimpl.go)
- Output boundaries: diagnostics are rendered by tsc.CreateDiagnosticReporter to sys.Writer (stdout), emitted files go through vfs.FS.WriteFile, .tsbuildinfo is written by the incremental layer, and --diagnostics stats/printed lists go to the writer. — [tsc/internal/execute/tsc/diagnostics.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/diagnostics.go) [tsc/internal/execute/tsc/emit.go#L115-140](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/emit.go#L115-L140) [tsc/internal/execute/incremental/snapshottobuildinfo.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/incremental/snapshottobuildinfo.go)

Every claim links to its cited files at the pinned commit. Citations identify source evidence; they do not establish runtime correctness. Independent CodeVetter scan — not reviewed by upstream maintainers.

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