Code Completions

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/lib/es2023.array.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/stringCompletions.ts
• src/services/types.ts
• src/services/utilities.ts
• src/testRunner/unittests/tsserver/exportMapCache.ts
• tests/baselines/reference/api/typescript.d.ts
• tests/baselines/reference/completionEntryForUnionMethod.baseline
• tests/baselines/reference/completionsCommentsClass.baseline
• tests/baselines/reference/completionsCommentsClassMembers.baseline
• tests/baselines/reference/completionsCommentsCommentParsing.baseline
• tests/baselines/reference/completionsCommentsFunctionDeclaration.baseline
• tests/baselines/reference/completionsCommentsFunctionExpression.baseline
• tests/baselines/reference/completionsCommitCharactersAfterDot.baseline
• tests/baselines/reference/completionsCommitCharactersExportImportClause.baseline
• tests/baselines/reference/completionsCommitCharactersGlobal.baseline
• tests/baselines/reference/completionsInitializerCommitCharacter.baseline
• tests/baselines/reference/completionsJSDocTags.baseline
• tests/baselines/reference/completionsSalsaMethodsOnAssignedFunctionExpressions.baseline
• tests/baselines/reference/completionsStringCommitCharacter.baseline
• tests/baselines/reference/goToTypeDefinition_Pick.baseline.jsonc
• tests/baselines/reference/goToTypeDefinition_arrayType.baseline.jsonc
• tests/baselines/reference/goToTypeDefinition_promiseType.baseline.jsonc
• tests/baselines/reference/goToTypeDefinition_typeReference.baseline.jsonc
• tests/baselines/reference/tsserver/exportMapCache/invalidates-the-cache-when-a-file-is-opened-with-different-contents.js
• tests/cases/fourslash/completionsCommitCharactersAfterDot.ts
• tests/cases/fourslash/completionsCommitCharactersExportImportClause.ts
• tests/cases/fourslash/fourslash.ts
• tests/cases/fourslash/goToTypeDefinition_Pick.ts
• tests/cases/fourslash/goToTypeDefinition_arrayType.ts
• tests/cases/fourslash/goToTypeDefinition_promiseType.ts
• tests/cases/fourslash/goToTypeDefinition_typeReference.ts
• tests/cases/fourslash/server/completionsOverridingMethodCrash2.ts

This document describes the code completion system that provides IntelliSense suggestions for identifiers, members, keywords, imports, and other code elements. For information about signature help (parameter hints), see Signature Help. For refactoring operations, see Refactorings.

Overview

The code completion system is responsible for generating contextually-appropriate suggestions when a user types code in an editor. The system analyzes the cursor position, determines the syntactic and semantic context, gathers candidate symbols from local scopes and imported modules, filters and ranks them based on relevance, and returns completion entries to the editor.

The main entry point is getCompletionsAtPosition src/services/services.ts1330 which returns a CompletionInfo src/services/types.ts741-755 object containing completion entries. Clients can then request additional details for specific entries via getCompletionEntryDetails src/services/services.ts1332

Architecture

The completion system is implemented primarily in the language service layer and relies on the type checker for semantic information.

Sources: src/services/services.ts1330-1340 src/services/completions.ts1-100

Main Entry Point

The getCompletionsAtPosition function in services.ts calls into the Completions namespace in completions.ts:

Sources: src/services/completions.ts150-400

Context Detection

The getCompletionData src/services/completions.ts1210 function determines what kind of completion is appropriate based on the cursor position. It examines the AST node at the position and surrounding context using findPrecedingToken src/compiler/utilities.ts6012

Context Types

Context Type	Description	Example
StringLiteral	Inside string literals for paths, JSX attributes	import * from "█"
MemberAccess	After dot or bracket operator	obj.█
GlobalsCompletion	Unqualified identifier position	const x = █
TypeOnlyLocation	Type annotation position	const x: █
JsDocTagContext	Inside JSDoc comment	/** @param █ */
JsxContext	JSX tag names or attributes	<Component █ />

Sources: src/services/completions.ts1210-1800 src/services/stringCompletions.ts14

Candidate Collection

Once the context is determined, the system collects candidate symbols from various sources:

Symbol Sources

Sources: src/services/completions.ts2500-3500 src/services/exportInfoMap.ts12

Member Completions

For member access expressions (object.█), the system:

1. Resolves the type of the left-hand side expression using checker.getTypeAtLocation src/compiler/checker.ts3815
2. Gets accessible properties from the type using checker.getPropertiesOfType src/compiler/checker.ts31110
3. Filters based on visibility using checker.isSymbolAccessible src/compiler/checker.ts28540

Sources: src/services/completions.ts2000-2800

Auto-Import Completions

The auto-import system provides completions for symbols available from other modules.

Key Data Structures:

• ExportInfoMap: Maps symbol names to their export locations src/services/exportInfoMap.ts12
• CompletionEntryDataAutoImport: Contains module specifier and position src/services/types.ts717-724
• IncompleteCompletionsCache: Caches partial results src/server/editorServices.ts68

Sources: src/services/completions.ts4000-5000 src/compiler/moduleSpecifiers.ts1-100

String Literal Completions

The StringCompletions src/services/stringCompletions.ts14 namespace handles completions for import paths and other string contexts.

Import Path Completions

The system offers:

• File system paths relative to current file via getFileSystemCompletions src/services/stringCompletions.ts310
• Node modules from node_modules/.
• Path mappings from tsconfig.json.

Sources: src/services/stringCompletions.ts14-500

Filtering and Ranking

The system filters and ranks completion candidates to present the most relevant suggestions first.

Ranking Algorithm

Completions are ranked using a sortText field. SortText src/services/completions.ts44-55 enumeration defines the priority levels:

• LocalDeclarationPriority: "0"
• LocationPriority: "1"
• OptionalMember: "2"
• MemberDeclaredBySpreadAssignment: "3"
• SuggestedClassMembers: "4"
• GlobalsOrKeywords: "5"
• AutoImportSuggestions: "6"
• JavascriptIdentifiers: "7"

Sources: src/services/completions.ts44-70

Completion Entry Details

getCompletionEntryDetails src/services/services.ts1332 provides:

• Documentation: JSDoc comments via symbol.getDocumentationComment src/compiler/checker.ts5430
• Type information: Display parts via typeChecker.typeToString src/compiler/checker.ts4890
• Code actions: Auto-import statements via importFixes.getImportCodeActions src/services/codefixes/importFixes.ts120

Sources: src/services/completions.ts6500-7500

JSDoc and JSX Completions

• JSDoc: Handled by getJSDocTagCompletions src/services/completions.ts2850
• JSX: Handled by getJSXCompletions src/services/completions.ts3200 providing attribute and tag name suggestions based on the intrinsic or component type.

Sources: src/services/completions.ts2800-3800

Integration Points

• Type Checker: Provides semantic information about symbols and types src/compiler/checker.ts117
• Module Specifier Resolution: Determines import paths src/compiler/moduleSpecifiers.ts1-100
• Language Server (tsserver): Exposes completions via the completionInfo command tests/baselines/reference/api/typescript.d.ts59

Sources: src/compiler/checker.ts117 src/server/protocol.ts1-100