PolySymbols

PolySymbols is a framework built on top of the platform's Symbol API (PolySymbol : Symbol) for sharing symbol definitions and code-insight features (completion, references, documentation, navigation, rename, find-usages, semantic highlighting) across languages and frameworks. It was called "Web Symbols" in 2022.3–2025.1 and is still marked experimental. Core module: community/platform/polySymbols/ (src, backend, src-web).

Do not modify PolySymbols platform source

Never edit anything under community/platform/polySymbols/** without the user's explicit, one-time permission for that specific change — not even a small, purely-additive generalization that looks obviously safe. This is shared framework code consumed by every PolySymbols integration in the repo (Angular, Vue, CSS, JS, GDScript, mermaid, etc.); a "safe-looking" generalization made to fix one integration's test can silently change behavior for all the others. If you hit a real gap or limitation in platform behavior while integrating a language/framework, the default response is to report it and ask, not to patch the platform — the right fix is almost always something owned by your own plugin (a plugin-registered EP implementation, e.g. its own UsageSearcher/ RenameUsageSearcher/CustomUsageSearcher, not a platform-file edit). This was learned the hard way: a session generalized PolySymbolUsageSearcher's PsiLinkedPolySymbol-only raw-PSI-reference bridge to also cover PolySymbolDeclaredInPsi, when the actual, documented platform design is that PolySymbolDeclaredInPsi intentionally does not provide that bridge (see references/query-model.md) — the fix should have stopped at "ask the user," not at "patch the framework."

Implementing a new integration typically means: build declaration/reference/completion providers on the platform side as usual, plus a handful of PolySymbols contributor classes — find-usages, documentation, and rename then work automatically through reference resolution to a PolySymbol.

Consumer code must not cast to a concrete symbol class

Code that consumes PolySymbols (annotators, inspections, completion/line-marker/parameter-info providers — and a language integration's own customizers/scopes, not just downstream callers) should never cast a PolySymbol to a concrete implementation class to detect its kind or read its data. This is explicitly documented in PolySymbol.kt's own "## Properties" doc comment ("when you get results from a PolySymbolQueryExecutor query, you should avoid casting symbols to specialized interfaces... a query may return symbols of unexpected classes contributed by some 3rd party plugins") — it is a platform convention every consumer is expected to follow, not a one-off rule:

• Kind detection → check the kind property (symbol.kind == SomeKind), which is always available on the plain PolySymbol interface. Never is ConcreteLeafSymbolClass.
• Any other data (a type, a signature, a navigable element, a boolean flag not expressible via kind) → define a PolySymbolProperty<T> object and annotate the concrete class's real member with @PolySymbol.Property(TheProperty::class), then read it via symbol[TheProperty] (the PolySymbol.get operator) — never (symbol as? ConcreteLeafSymbolClass)?.someMember.
• Package the property behind a PolySymbol.xxx extension, so consumer call sites read symbol.xxx and never see the property object or a cast at all — mirror plugins/JavaScriptLanguage/web-platform/src/com/intellij/polySymbols/js/JSSymbolUtils.kt's PolySymbol.jsType/jsKind/toPropertySignature, the reference example cited in PolySymbol.kt itself. Note toPropertySignature's fallback branch (when the property is absent) builds its result purely from other plain PolySymbol members (name, modifiers, jsType) — it never casts, not even as a fallback.
• A shared, uniformly-implemented interface across a framework's own symbol kinds (e.g. GDScript's GdClassSymbol, exposing directMemberScope/resolveSuperClassSymbol() identically from both PSI- and SDK-backed class symbols) is not what this rule targets — that's legitimate polymorphic dispatch within a framework's own resolution machinery, not "cast down to read hidden, kind/backing-specific data" in consumer code. The anti-pattern is casting to a leaf class (GdPsiMethodSymbol, GdSdkClassSymbol) or a backing-specific base (GdPsiPolySymbol vs. GdSdkPolySymbol) from outside the symbol-definition package.
• Reflection technique worth knowing: a @PolySymbol.Property-annotated member declared once on a shared abstract base class is found by every subclass automatically — PolySymbolPropertyGetter walks superclasses/interfaces when building its per-concrete-class accessor map, and Java/Kotlin generate a bridge method (matching the base class's erased signature) for any subclass override with a covariant return type, which is exactly what Method.invoke() resolves against. So you don't need to repeat the annotation on every leaf subclass when the member is inherited unchanged.

Interface cheat sheet

Interface / class	Purpose
PolySymbol	Core element — kind (namespace + kindName) + name, plus optional icon/priority/modifiers/apiStatus/pattern
PolySymbolScope	A symbol that contains other symbols (an HTML element containing attributes, a JS class containing members)
PolySymbolQueryExecutor / Factory	Runs nameMatchQuery/listSymbolsQuery/codeCompletionQuery against contributed scopes
PolySymbolQueryScopeContributor	Registers PolySymbolScopes for a PSI location — the main extension point you implement
PolySymbolQueryConfigurator	Supplies PolyContext rules + symbol name-conversion rules
PsiPolySymbolReferenceProvider	Resolves a host PsiElement to a referenced PolySymbol — registered via EP, produces external references
PolySymbolOwnReferences	Alternative to PsiPolySymbolReferenceProvider: builds references to return from PsiElement.getOwnReferences() directly — a language's own canonical resolve, not EP-registered. Requires the host element to implement the PolySymbolOwnReferenceHost marker interface
PolySymbolDeclarationProvider	Supplies PolySymbolDeclarations for a PsiElement (skip if PsiLinkedPolySymbol covers your case)
PolySymbolsCompletionProviderBase	Base class for a CompletionProvider that runs a codeCompletionQuery
PolySymbolWithPattern	A symbol expanded via a microsyntax pattern into a PolySymbolMatch
PsiLinkedPolySymbol	A symbol backed 1:1 by a real PsiElement — gets declarations/navigation/find-usages "for free"
ReferencingPolySymbol	Utility: makes one symbol kind stand in for/alias another kind
PolyContext	Gates scopes/configurators here, but is a general-purpose, performance-optimized context API usable well beyond PolySymbols — see poly-context
Web Types	Static JSON symbol definitions — see references/web-types.md

See references/query-model.md for the full query/scope/declaration/ reference/completion wiring, and references/patterns.md for the pattern DSL and microsyntax matching.

The rule: PolySymbols is additive, not automatically authoritative

Every real integration studied in this repo keeps legacy PSI-based reference/completion code running alongside PolySymbols — none resolve entirely through it. This is not a migration artifact you can ignore; it is the load-bearing design fact for anyone adding a new integration. See references/case-studies.md for full detail, but the pattern repeats everywhere:

• JS/TS/HTML/CSS (the platform's own built-in support) grafts PolySymbols onto pre-existing extension points (XmlElementDescriptorProvider, css.elementDescriptorProvider, JSReferenceExpression.resolve()) and explicitly steps aside for standard/spec symbols — e.g. HtmlElementSymbolDescriptorsProvider.getElementDescriptor() returns null when the query result hasOnlyStandardHtmlSymbols(), deferring to the bundled RelaxNG HTML5 schema; the legacy CssElementDescriptorProviderImpl is kept registered with order="last" as the CSS fallback; TypeScriptReferenceExpressionResolver only consults PolySymbols for unqualified references inside injected/embedded expression hosts. Standard tag/attribute/property lists are not Web Types data — they're the pre-existing RelaxNG schema and webref CSS XML.
• Vue and Angular — the docs' own "heaviest adopters" — are close to fully PolySymbols-driven for their template/markup surface (components, directives/selectors, props/inputs, slots, events, modifiers), but Vuex, <style src>/ref=/file-path references, and CSS v-bind() bindings (Vue), and the Angular2 expression-language layer, templateUrl/pipe-name references (Angular) all still run through plain PsiReferenceContributor/CompletionContributor code with no PolySymbols involvement at all.
• GDScript, the newest integration, is explicitly dual-track by its own admission — its in-tree README (dotnet/Plugins/godot-support/gdscript/.../polySymbols/README.md) states the PSI and PolySymbols implementations both run today and produce duplicate Find Usages results until the legacy path is deleted. Local variables, parameters, for-loop bindings, resource-path references, and the entire TSCN language have no PolySymbols coverage yet.

Actionable takeaway: for every new integration or feature, decide explicitly whether PolySymbols is the resolution path of record for that PSI element/feature, or merely a supplementary layer contributing extra symbols on top of an existing mechanism. If a legacy PsiReferenceContributor/CompletionContributor and a new PolySymbols registration can both fire on the same host PsiElement, either gate one off (a feature flag, a context check, an early return null/empty-list from whichever should defer) or accept and document the overlap — don't assume the platform will pick one for you.

Wiring checklist — adding PolySymbol support

1. Opt the language in: register polySymbols.enableInLanguage language="..." (EP com.intellij.polySymbols.enableInLanguage) so PsiExternalReferenceHosts in that language are eligible for PolySymbols reference resolution at all.
2. Contribute scopes: implement PolySymbolQueryScopeContributor (EP com.intellij.polySymbols.queryScopeContributor) — map PSI locations to PolySymbolScopes via the registrar DSL. This is almost always the first and most important class you write. Details: references/query-model.md.
3. Resolve references: implement PsiPolySymbolReferenceProvider per host PsiElement type (EP com.intellij.polySymbols.psiReferenceProvider, one registration per hostElementClass). Alternative: implement PsiElement.getOwnReferences() directly via the PolySymbolOwnReferences builder when PolySymbols should be the language's own canonical resolve rather than an EP-contributed layer (e.g. replacing a legacy PsiReferenceContributor) — see references/query-model.md. Don't register both for the same host — own references pre-empt external ones. Either way, the host element's own type must implement PsiExternalReferenceHost (external) or PolySymbolOwnReferenceHost (own) — PolySymbolHighlightingAnnotator only looks at elements implementing one of the two, so skipping this isn't just a missed nicety, it's silently no highlighting/diagnostics at all (own references also won't compile against the DSL without it).
4. Supply declarations: if a symbol maps 1:1 onto a real PsiElement and lives purely in the PolySymbols model, implement PolySymbolDeclaredInPsi plus a PolySymbolDeclarationProvider (EP com.intellij.polySymbols.declarationProvider) that builds the symbol — this is the default. The provider is pure dispatch: decide which symbol(s) a PsiElement backs, instantiate them, and return symbol.declaration (the interface's own default). Don't hand-roll a PolySymbolDeclaration implementation or thread a range through the provider — a non-default declaration range is a textRangeInSourceElement override on the symbol class itself; the symbol represents itself, the provider only knows which symbol to build. Reach for PsiLinkedPolySymbol + polySymbols.psiLinkedSymbol host="..." only when that same PsiElement must also keep working as a target for a legacy, non-PolySymbols find-usages/rename mechanism you're running alongside (a bridge for partial migrations, not a general shortcut — see references/query-model.md). For symbols with no backing PsiElement at all (synthetic/SDK symbols), write a PolySymbolDeclarationProvider by hand.
5. Wire completion: register an ordinary completion.contributor whose provider extends PolySymbolsCompletionProviderBase and calls queryExecutor.codeCompletionQuery(...).
6. Optional: PolySymbolQueryConfigurator for context rules/name-conversion rules; PolySymbolQueryResultsCustomizerFactory to post-filter/remap query results; polySymbols.webTypes if standard-library symbols can be shipped as static JSON instead of code (see references/web-types.md); a PolySymbolFramework (polySymbols.framework) + PolyContextProvider (polySymbols.context) if you're introducing a new framework identity (see poly-context).
7. Use PolySymbolWithPattern/the pattern DSL when the language/framework layers a microsyntax on top of base syntax (directive-style attribute names, event-modifier chains). See references/patterns.md.

Case studies

Four real integrations in this repo, each ending in an explicit PolySymbols-vs-legacy verdict — read references/case-studies.md for the full writeup with file:line evidence.

Integration	Where	One-line verdict
GDScript	dotnet/Plugins/godot-support/gdscript/.../polySymbols/	Dual-track: SDK/engine symbols are PolySymbols-first; user-code locals, resource refs, and TSCN are legacy-only, both paths run concurrently on some elements
JS/TS, HTML, CSS	plugins/JavaScriptLanguage/web-platform/, community/xml, plugins/css	PolySymbols is grafted onto legacy extension points and steps aside for anything standard/spec-defined
Vue	contrib/vuejs/vuejs-backend/src/org/jetbrains/vuejs/web/	Template/markup surface (components/directives/props/slots/events) is ~fully PolySymbols; Vuex, refs, CSS bindings are not
Angular	contrib/Angular/angular-backend/src/org/angular2/web/	Markup/selector surface is ~fully PolySymbols; the Angular2 expression-language layer and some file/pipe-name refs are not

Related skills

• symbols-api — the Symbol foundation this framework builds on.
• poly-context — framework/environment detection.
• Official docs: Poly Symbols, Implementing Poly Symbols, Poly Symbols Integration with Language Features.

Supporting files

Load only when needed:

• Query model — query executor, scopes, contributors, configurators, declarations, references, completion, search/rename/nav hookups.
• Patterns — the pattern DSL, PolySymbolMatch/name segments, ReferencingPolySymbol, the Vue directive worked example.
• Case studies — GDScript, JS/TS/HTML/CSS, Vue, Angular, in depth.
• Web Types — static JSON symbol definitions.
• Testing — writing tests for a PolySymbols integration: the PolySymbolsTestCase hierarchy, the PolySymbolsTestUtil.kt cheat sheet, feature-by-feature recipes.
• Migration — migrating a PSI-based feature to PolySymbols, tests-first: the preliminary-tests-migration recipe, forbidden CodeInsightTestFixture methods, the per-kind production migration unit.