Symbol API

com.intellij.model.Symbol (community/platform/core-api/src/com/intellij/model/Symbol.java) is the platform's generic replacement for "resolve a PsiReference to a PsiElement". A Symbol represents a semantic element in some model — a language, a framework, a database schema — and decouples navigation/find-usages/rename/documentation from PSI. A Symbol is not required to be backed by a PsiElement, and it is incorrect to try to obtain one from a Symbol.

Canonical examples from the docs: a Java local variable (backed by PsiVariable), a compiled class from JDK stubs (not tied to any project), a Spring bean (created dynamically by framework support, project-bound but not PSI-backed), a database column (defined by a data source, not PSI-backed and not project-bound).

Before hand-wiring any of the mechanisms on this page, look at poly-symbols first. PolySymbol : Symbol, and the PolySymbols framework exists specifically to save you from writing this boilerplate by hand — its query executor, completion-provider base class, and default searchTarget/renameTarget/ getDocumentationTarget/getNavigationTargets implementations give you declarations, references, completion, search, rename, and navigation with a fraction of the code this page documents. Treat PolySymbols as the default, go-to way to implement a new language or framework's symbol support — it is not limited to cross-language microsyntax sharing, that's simply the feature that falls out for free once the query/pattern machinery exists. Reach for the raw Symbol/ PsiSymbolReference API on this page directly only when a symbol genuinely doesn't fit PolySymbols' model: a single, self-contained resolve with no query/completion surface of its own (a format-string placeholder resolved from one call expression, a markdown link label), or something not project-bound / not PSI-backed at all (a compiled-class symbol from JDK stubs, a database column) where the extra query/scope layer would add nothing.

Contract and lifecycle

public interface Symbol {
  @NotNull Pointer<? extends Symbol> createPointer();
  @Override boolean equals(Object obj);
  @Override int hashCode();
}

• equals/hashCode must reflect semantic identity, not object identity — the platform uses Symbol as a cache key and de-duplicates concurrently-computed instances that are equal.
• Lifecycle is a single read action. A Symbol is safe to pass between APIs within one read action, but must not be referenced across read actions. Call createPointer() while still valid, store the Pointer, and call Pointer.dereference() in the next read action to get a fresh (or the same, if still valid) instance.
• All of this applies unchanged to PolySymbol, which extends Symbol.

Declarations

Model where a symbol is declared in a PSI tree via PsiSymbolDeclaration (community/platform/core-api/src/com/intellij/model/psi/PsiSymbolDeclaration.java): getDeclaringElement(), getRangeInDeclaringElement(), getSymbol(). A symbol can have zero declarations (files — "only references"), one (a Java local variable), or several (a C# partial class, a property key declared in multiple files).

Two ways to supply declarations:

• Register a PsiSymbolDeclarationProvider (getDeclarations(element, offsetInElement)) at EP com.intellij.psi.declarationProvider. The platform calls it for each PsiElement from the leaf at the caret up to the containing file, with offsetInElement as a hint (-1 means "all declarations").
• Implement PsiSymbolDeclaration directly on the PsiElement.

References — three kinds

References are modeled by PsiSymbolReference (community/platform/core-api/src/com/intellij/model/psi/PsiSymbolReference.java): getElement(), getRangeInElement(), resolveReference(): Collection<? extends Symbol> (empty collection = unresolved), and resolvesTo(target) (override to short-circuit before a full resolve, e.g. by comparing text first). For the common single-target case, extend SingleTargetReference.

Kind	When	Mechanism
Own	Reference is intrinsic to the language itself (e.g. x in x * 2 referencing var x = 42)	PsiElement.getOwnReferences()
External	Reference is not recognized by the host language, contributed by another plugin (e.g. a filename string in new File("users.txt"))	Host implements PsiExternalReferenceHost; other plugins register a PsiSymbolReferenceProvider
Implicit	Reference only supports resolving to a target (navigation, hover doc) — not find-usages/rename starting from the target (e.g. var in var x = new Person())	ImplicitReferenceProvider

Language support should not assume external references are absent — they may be contributed by any plugin. Own vs. external is a modeling choice about who "owns" the reference semantics, not a technical distinction in PsiSymbolReference itself.

External references — PsiSymbolReferenceProvider

Interface (community/platform/core-api/src/com/intellij/model/psi/PsiSymbolReferenceProvider.java):

public interface PsiSymbolReferenceProvider {
  Collection<? extends PsiSymbolReference> getReferences(PsiExternalReferenceHost element, PsiSymbolReferenceHints hints);
  Collection<? extends SearchRequest> getSearchRequests(Project project, Symbol target);
}

Register via PsiSymbolReferenceProviderBean at EP com.intellij.psi.symbolReferenceProvider, declaring hostLanguage, hostElementClass, targetClass (common supertype of resolved symbols), referenceClass (defaults to PsiSymbolReference; narrow it so the platform can skip providers that can't possibly answer a query for a more specific reference type), and implementationClass.

Worked examples in this repo:

• community/java/java-impl/src/com/siyeh/ig/format/StringFormatSymbolReferenceProvider.java — resolves %s/{0}-style placeholders inside String.format/printf/MessageFormat call arguments back to the corresponding call argument, complete with its own Symbol (FormatArgumentSymbol-style), NavigatableSymbol, and a SearchTarget/rename-capable design — read this file end to end as the reference implementation for "symbol lives inside a string literal, references live inside sibling call arguments."
• community/jvm/jvm-analysis-impl/src/com/intellij/analysis/logging/resolve/LoggingArgumentSymbolReferenceProvider.kt — the same idea for JVM logging framework {}/{0} placeholders across Java/Kotlin.
• Markdown link-label resolution (linked from the official docs as a third sample) follows the same shape one level simpler: label text in [text][label] resolves to the [label]: url definition.

Implicit references — ImplicitReferenceProvider

(community/platform/core-api/src/com/intellij/model/psi/ImplicitReferenceProvider.java, EP com.intellij.psi.implicitReferenceProvider):

public interface ImplicitReferenceProvider {
  default PsiSymbolReference getImplicitReference(PsiElement element, int offsetInElement) { ... }
  default Collection<? extends Symbol> resolveAsReference(PsiElement element) { return emptyList(); }
}

Usually you only override resolveAsReference — the default getImplicitReference wraps a non-empty result in an ImmediatePsiSymbolReference. This enables navigation and hover-link highlighting on the target Symbol, but the platform will never find this "reference" via find-usages or rename-from-target, because it was never indexed as a searchable reference. Called for every element from the caret leaf up to the file — keep it cheap.

PolySymbols' PsiPolySymbolReferenceProvider is built on top of exactly this external-reference mechanism, but replaces the manual getReferences/getSearchRequests plumbing with a single getReferencedSymbol(element): PolySymbol? you implement once — resolution, search, and rename all follow from the returned symbol. Prefer it over hand-writing PsiSymbolReferenceProvider unless you have a concrete reason not to — see the "References" section of poly-symbols/references/query-model.md.

Hooking a Symbol into platform features

A bare Symbol only gives you resolve. To light up the rest of the IDE, implement (or delegate to) these on your Symbol/PolySymbol:

Feature	Interface	Notes
Navigation	NavigatableSymbol (community/platform/core-api/src/com/intellij/navigation/NavigatableSymbol.java)	getNavigationTargets(project); SymbolNavigationService helps build NavigationTargets
Find usages	SearchTarget/SearchTargetSymbol (community/platform/lang-impl/src/com/intellij/find/usages/api/SearchTarget.kt)	presentation(), usageHandler, maximalSearchScope, textSearchRequests; register a factory at com.intellij.lang.symbolSearchTarget if you don't want the Symbol itself to implement it
Rename	RenameableSymbol/RenameTarget (community/platform/lang-impl/src/com/intellij/refactoring/rename/symbol/RenameableSymbol.kt)	or register a SymbolRenameTargetFactory at com.intellij.rename.symbolRenameTargetFactory
Documentation	DocumentationTarget	via PsiSymbolReferenceService/language-specific hookup

PolySymbol (see poly-symbols) already wires all four of these through searchTarget/renameTarget/getDocumentationTarget/getNavigationTargets properties with sensible defaults. This is the general pattern across this whole page: almost everything above is what PolySymbol implements for you. Implement PolySymbol and get all four; implementing raw Symbol means writing every row of the table above by hand for every symbol kind you add.

Related

• poly-symbols — start here for new language/framework symbol support. It's built on Symbol and is the intended default implementation path, not a specialized add-on — reach for the mechanisms on this page directly only when a symbol falls outside its model (see the decision note above).
• poly-context — general-purpose, performance-optimized context detection; PolySymbols is one consumer, not a dependency.
• Official docs: Symbols, Declarations and References.