Glossary

Project-specific terms used throughout the codebase. For broader TypeScript language vocabulary (generics, conditional types, etc.) consult the TypeScript handbook.

Core compiler terms

• AST / Node — the parsed syntax tree. Every parsed token, expression, statement, and declaration is a Node with a kind: SyntaxKind. See primitives/node.
• SourceFile — the root Node of one parsed .ts / .tsx / .js / .d.ts file. See primitives/source-file.
• SyntaxKind — the enum (in src/compiler/types.ts) that tags every node and every token.
• Symbol — the binder's record of a named declaration. One symbol can have multiple declarations (e.g., merged interfaces). See primitives/symbol.
• Type — the checker's view of a value. Types are usually flyweighted via TypeFlags. See primitives/type.
• Signature — a function or constructor signature (parameters, return type, type parameters). See primitives/signature.
• FlowNode — a node in the flow graph the binder produces and the checker walks for control-flow narrowing.
• Diagnostic — a single error/warning/suggestion message produced by the compiler or the language service. See primitives/diagnostic.
• Path — a branded string for an absolute, normalized, canonical filesystem path. Created by toPath(). Used as a key into source-file/program maps.
• Program — the immutable bundle of source files, options, references, and the lazily created type checker. See systems/program.
• CompilerHost / LanguageServiceHost — the abstraction the compiler/language-service uses to talk to a filesystem-like environment. See systems/program and systems/language-service.

Pipeline phases

• Scan — turn text into tokens (scanner.ts).
• Parse — turn tokens into a tree (parser.ts); produces SourceFile.
• Bind — walk the tree to compute symbols, container relationships, flow nodes (binder.ts).
• Check — answer type queries on demand (checker.ts).
• Transform — lower newer syntax/semantics into older targets (transformer.ts, transformers/*).
• Emit — print transformed trees as .js, .d.ts, or source maps (emitter.ts).
• Resolve — find the file referenced by an import specifier (moduleNameResolver.ts, resolutionCache.ts).

Editor / project terms

• tsserver — the standalone language server process (src/server/).
• Project — tsserver's runtime concept of a compilation unit. Variants: ConfiguredProject (backed by a tsconfig.json), InferredProject (loose files), ExternalProject (driven by an embedder like Visual Studio's project system), AutoImportProvider (a derived project used to compute auto-imports).
• ScriptInfo — tsserver's record for one file: its open/closed state, content snapshot, attached projects, etc. (src/server/scriptInfo.ts)
• EditorServices — the project-graph manager owned by tsserver (src/server/editorServices.ts).
• Refactor / CodeFix — language-service operations that produce file edits. See features/refactors-and-codefixes.
• Fourslash — the DSL used in tests/cases/fourslash/ for language-service tests. See how-to-contribute/testing.

Build / tooling terms

• LKG — last known good. The compiler under lib/ used to bootstrap a build. hereby LKG promotes the local build into LKG.
• hereby — the gulp-style task runner that drives builds, tests, lint, and packaging.
• dprint — the formatter used by hereby format.
• Knip — dead-code/unused-export checker run by hereby knip.
• Baseline — an expected-output snapshot under tests/baselines/reference/. Tests compare their output to baselines and fail on diff.
• Twoslash — a comment-marker DSL inside .ts test files used for cursor positions, error expectations, and other meta-information.

ATA / typings

• ATA — Automatic Type Acquisition. tsserver asks typingsInstaller to fetch @types/* packages for plain JavaScript projects so editor features work. See systems/automatic-type-acquisition.
• Typings cache — the per-user directory where ATA stores acquired packages.

Module / target terms

• Target — the JavaScript output level (ES5, ES2015, …, ES2022, ESNext). Selects which transformers run and which library .d.ts files are loaded.
• Module — the module-system kind for emit and import resolution: none, commonjs, amd, umd, system, es2015, es2020, es2022, esnext, node16, node18, node20, nodenext, preserve.
• Library — --lib controls which lib.*.d.ts declaration files are auto-included.
• Project references — multi-project builds via references in tsconfig.json. See systems/build-mode.

Diagnostic categories

• Error — fatal type or syntax error (red squiggle).
• Warning — non-fatal but flagged.
• Suggestion — surfaced only by the language service (e.g., unused-symbol suggestions).
• Message — informational (used for things like "Cannot find name" hints).

Frequently-used abbreviations

Abbrev	Meaning
LS	Language service
LSH	Language service host
CFA	Control-flow analysis
TSC	The compiler executable (tsc)
LKG	Last known good (the bootstrapping compiler in lib/)
DOM lib	The auto-generated lib.dom.d.ts
ATA	Automatic type acquisition
RWC / RWA	Real-world-code test runner (legacy)