kotlin java c language_server

Ultra-lightweight VSCode extension + Language Server Protocol (LSP) lightweight server for Kotlin, Java, C and C++ files.

Supported features

• Kotlin (.kt, .kts), Java (.java), C (.c, .h), and C++ (.cpp, .cc, .cxx, .hpp, .hh, .hxx) documents
• Kotlin syntax highlighting (TextMate grammar)
• Document Symbol (@ in VSCode quick open): lists symbols for current file
• Breadcrumb symbol path: shows the current Kotlin / Java / C type and function or method in the editor path bar when Breadcrumbs are enabled
• Go to Definition (F12 / cmd-click): resolves symbols from open documents, then falls back to full-project scan, and finally to bundled Kotlin / Java / JVM API stubs. Qualified member calls use receiver types, explicit imports, and supported inheritance/extension declarations. The extension's explicit F12 command can open documentation fallback when no definition target is found and kotlinJavaCLanguageServer.definitionFallback.enabled is enabled; background provider requests and Ctrl/Cmd-click never open documentation automatically
• Callback/type navigation: explicit named Kotlin lambda inputs use supported visible function/constructor callback signatures; Java block-body lambdas can use directly declared non-generic SAMs. Go to Type Definition is separate from F12 on a variable/parameter. Unknown/conflicting callback inputs are not guessed. See supported cases and limits.
• Bundled API stubs: F12 on Kotlin stdlib helpers (isNotBlank, firstOrNull, let, apply, etc.), common Java APIs, and imported javax.inject / jakarta.inject types opens bundled reference stubs with usage explanations, examples, API-specific caveats and documentation links
• Workspace Symbol (# in quick open): searches open documents first, then falls back to full-project scan when no match is found
• Quick Symbol Search in Project (editor right-click menu): searches the workspace from the word under cursor and provides jump targets
• Quick Reference Search in Project (Cmd+Alt+R / Ctrl+Alt+R, or editor right-click menu): finds every usage of the symbol under the cursor across the workspace. Behaves like Goto Definition — a single match jumps directly, multiple matches open VS Code's inline Peek view
• Explain Unknown Symbol (editor right-click menu / Command Palette): when the symbol under the cursor has no local/project/bundled-stub definition target, opens an in-editor documentation result page with official Kotlin / Java / Android / C / C++ summaries, declarations, details, and reference links where available
• Class literal navigation: Supported imported Kotlin Type::class / @Throws references and Java Type.class references resolve to type declarations, including aliases and unopened source files; ::class is not treated as a parameter declaration.
• Explicit enclosing receivers: Supported this.member, this@Outer.member, and super@Outer.member expressions resolve through the lexical class hierarchy. Imported nested classes are matched by their declaration paths rather than treating enclosing classes as packages.
• Kotlin type references: Default-imported collection, core, and sequence types such as List, MutableList, Map, String, and Array jump to bundled declarations; supported collection members also resolve through their declared supertypes.
• Apollo GraphQL navigation: Kotlin imports and supported nested response-model types jump to .graphql/.gql operation and response-field selections using literal Apollo package/source-directory configuration. Default semantic operation suffixes and response aliases are supported; no build or network access is required. See scope and examples.
• GraphQL enum members: Follow supported typed response-field chains using a local Apollo introspection schema. data.goldCurrency?.name navigates to the bundled kotlin.Enum.name declaration only when the selected field is proven to be an enum with default enum-class generation; selected response fields navigate to the GraphQL operation. Missing/scalar/list/conflicting schemas are not guessed.
• AndroidX children callbacks: Explicit forEach/forEachIndexed inputs on the imported androidx.core.view.children property can resolve to android.view.View for proven ViewGroup/RecyclerView receivers, including visible project View extensions. Unknown receivers or shadowed declarations are not guessed.
• Gradle BuildConfig fields: BuildConfig.FIELD jumps to literal buildConfigField or Android Components buildConfigFields declarations in the corresponding module's Kotlin/Groovy Gradle build script. Multiple flavor declarations remain selectable. Gradle expressions and convention plugins are not evaluated.
• AndroidX RecyclerView constants: Qualified SCROLL_STATE_IDLE, SCROLL_STATE_DRAGGING, and SCROLL_STATE_SETTLING navigate to bundled reference declarations through the normal definition provider, including Ctrl/Cmd-click.
• Android member documentation fallback: When source lookup finds no target, explicit F12 resolves imported Android / AndroidX member owners and opens the official class reference at the member anchor. F12 and Explain show progress while looking up definitions or documentation.
• Android ViewBinding mapping: ActivityDeviceInfoBinding automatically maps to res/layout*/activity_device_info.xml for direct jump

Lightweight declaration-based navigation, not a compiler type checker. Complex chained expressions, overload selection, wildcard type imports, and fully semantic references remain limited.

Offline API guides

All ten Kotlin/Java/injection/RecyclerView/C/C++ reference files have English API-level guides covering parameters/results through examples and explanations, null/empty behavior, exceptions, mutability, sequence evaluation, buffer bounds and ownership. Signatures and bodies remain abbreviated navigation placeholders, not compiled SDK implementations; verify target-version availability. javax.inject and jakarta.inject are different namespaces and must match the DI implementation.

Owned copies of extension reference assets are excluded from application lookup; genuine app assets with the same filenames remain searchable. Explicit F12 deduplicates identical provider selections but preserves distinct definitions.

Coverage and the unchanged-code gate: stub documentation audit. Run npm run docs:audit; after reviewing scripts/stub-guides-*.cjs, use node scripts/document-stubs.cjs . --apply and run npm test.

Architecture

• src/extension.ts: VSCode Language Client
• src/server.ts: Node-based LSP server
• src/symbols.ts: Kotlin / Java / C / C++ symbol parsing and cursor word extraction
• src/memberResolution.ts / src/callbackBindings.ts: conservative owner lookup, callback input declarations and lexical callback anchors

This follows the standard VSCode Language Client + Language Server split architecture.

Install dependencies

npm install

Build

npm run compile

Run in VSCode (manual review)

1. Open this repository in VSCode.
2. Run npm run compile.
3. Press F5 to launch an Extension Development Host.
4. In the new window, open a Kotlin, Java, or C file.
5. Verify:
   • Cmd+Shift+O (or quick open with @) shows symbols from current file.
   • Breadcrumbs show the current symbol path for Kotlin, Java, and C files when breadcrumbs.enabled is on.
   • F12 on a symbol jumps to its definition when the defining file is currently open.

Package and install in local VSCode

1. Install VSCE:

   npm install -D @vscode/vsce
   

2. Create VSIX:

   npx vsce package --allow-missing-repository
   

3. Install VSIX:

   code --install-extension kotlin-java-language-server-0.2.17.vsix