fix(navigation): show usages on a declaration a plugin's index links elsewhere

A plugin's document index can link a declaration's name elsewhere: MyBatis Duo links a mapper method to its XML statement. Go to Declaration followed such a link at once, in the editor and in the host, so ⌘B on the method jumped to the XML instead of showing its usages as it does on any declaration (and did for plugins that answer through a definition provider). When the syntax tree puts the caret on a declaration's name, the link is no longer followed directly: the language server's answer comes along and the usages show, the plugin's target among them. Elsewhere plugin links are followed as before, without waiting for the language server.

Fixes #3207

crates/ide-host/src/ops/lsp.rs

@@ -309,9 +309,13 @@ pub async fn lsp_signature_help(host: &Host, window: &str, doc: DocId, pos: Pos)
 
 pub async fn lsp_goto(host: &Host, window: &str, doc: DocId, pos: Pos, kind: GotoKind) -> IdeResult<Vec<Location>> {
     let target = position_document(host, window, doc, pos).await?;
+    // ⌘B on a declaration shows its usages, also when a plugin's index links the name elsewhere
+    // (a MyBatis mapper method to its XML statement): the server's answer comes along for the
+    // editor to tell.
     if target == doc
         && kind == GotoKind::Definition
         && let Some(plugins) = crate::plugins::editor_plugin_host()
+        && !on_declaration_name(host, window, doc, pos).await
     {
         let project = host.project(window)?;
         // A notebook cell is a language-server document only: no plugin navigates in it.
@@ -352,6 +356,30 @@ pub async fn lsp_goto(host: &Host, window: &str, doc: DocId, pos: Pos, kind: Got
     definition_targets(result, found, in_string)
 }
 
+/// Whether the syntax tree puts the identifier at `pos` as a declaration's name (`int f()`'s `f`).
+async fn on_declaration_name(host: &Host, window: &str, doc: DocId, pos: Pos) -> bool {
+    let Ok(project) = host.project(window) else { return false };
+    blocking(move || {
+        let snap = project.documents.text_snapshot(doc)?;
+        if snap.large {
+            return Ok(false);
+        }
+        let s = ide_syntax::Snapshot::doc(doc, snap.version, &snap.language, &snap.text);
+        let cancel = ide_core::CancellationToken::new();
+        let Ok(Some(at)) = project.structure.node_at(&s, Range::new(pos, pos), &cancel) else { return Ok(false) };
+        Ok(is_declaration_name(&at))
+    })
+    .await
+    .unwrap_or(false)
+}
+
+fn is_declaration_name(at: &ide_syntax::NodeAt) -> bool {
+    at.node.field.as_deref() == Some("name")
+        && at.ancestors.first().is_some_and(|parent| {
+            ["declaration", "definition", "declarator"].iter().any(|kind| parent.kind.ends_with(kind))
+        })
+}
+
 async fn in_string_literal(host: &Host, window: &str, doc: DocId, pos: Pos) -> bool {
     let Ok(project) = host.project(window) else { return false };
     blocking(move || {
@@ -2136,6 +2164,24 @@ mod tests {
         assert_eq!(paths(definition_targets(Ok(vec![helper, guess]), Vec::new(), false)), ["/p/app/helpers.php"]);
     }
 
+    #[test]
+    fn declaration_names_are_told_apart_from_uses() {
+        let syntax = std::sync::Arc::new(ide_language::Syntax::new());
+        let structure = ide_syntax::StructureService::new(std::sync::Arc::new(ide_language::SyntaxCache::new(syntax)));
+        let java = ide_core::LanguageId::new("java");
+        let text = "interface ShareMapper {\n    int batchCancel(List<Long> ids);\n}\nclass S { int f(ShareMapper m) { return m.batchCancel(null); } }\n";
+        let snap = ide_syntax::Snapshot::text(&java, text);
+        let cancel = ide_core::CancellationToken::new();
+        let at = |line, col| {
+            let pos = Pos::new(line, col);
+            is_declaration_name(&structure.node_at(&snap, Range::new(pos, pos), &cancel).unwrap().unwrap())
+        };
+        assert!(at(1, 10), "the mapper method's name");
+        assert!(at(0, 12), "the interface's name");
+        assert!(!at(3, 45), "a call of the method");
+        assert!(!at(1, 4), "its return type");
+    }
+
     #[test]
     fn positions_inside_string_literals_are_told_apart() {
         let syntax = std::sync::Arc::new(ide_language::Syntax::new());

src/editor/lsp/navigation.ts

@@ -63,6 +63,7 @@ import {
   SYNTAX_NOTE,
   declarationFallback,
   indexDefinitions,
+  isDeclarationName,
   isSelfTarget,
   localHighlights,
   type DeclarationTarget,
@@ -360,6 +361,15 @@ export async function gotoTargets(view: EditorView, kind: GotoKind, at?: number)
   }
 }
 
+/** Whether the caret is on the name of a declaration, by the syntax tree (no language server wait). */
+async function onDeclarationName(view: EditorView, offset: number): Promise<boolean> {
+  const doc = docOf(view);
+  if (!doc) return false;
+  const pos = offsetToPos(view.state.doc, offset);
+  const at = await structure.nodeAt(doc.doc, { start: pos, end: pos }).catch(() => null);
+  return isDeclarationName(at);
+}
+
 async function gotoResolved(
   view: EditorView,
   kind: GotoKind,
@@ -374,7 +384,10 @@ async function gotoResolved(
     const before = view.state.doc;
     const plugin = await contributedNavigation(view, offset).catch(() => null);
     if (view.state.doc !== before || superseded()) return;
-    if (plugin) {
+    // ⌘B on a declaration shows its usages, also when a plugin links the name elsewhere (a
+    // MyBatis mapper method to its XML statement).
+    if (plugin && !(kind === "definition" && (await onDeclarationName(view, offset)))) {
+      if (superseded()) return;
       if (plugin.targets.length === 1) await navigateTo(plugin.targets[0]!);
       else {
         const items = await locationItems(plugin.targets);

src/editor/lsp/syntaxFallback.test.ts

@@ -45,6 +45,7 @@ provideEditorService({ openFile } as never);
 
 const fb = await import("./syntaxFallback");
 const { gotoTargets, navigationExtension, highlightUsages } = await import("./navigation");
+const { registerNavigationProvider } = await import("@/editor/navigationProviders");
 const { startRename, renameNamePart } = await import("./rename");
 const { lspDoc } = await import("./lsp");
 const { invalidateConfigurationNavigation } = await import("./configurationNavigation");
@@ -416,6 +417,48 @@ describe("navigation wiring", () => {
     expect(openFile).not.toHaveBeenCalled();
   });
 
+  it("shows usages on a declaration a plugin's index links elsewhere, and follows the link from a call", async () => {
+    // MyBatis Duo indexes the mapper method's name as a link to its XML statement.
+    const xml = { path: "/p/UserMapper.xml", range: r(3, 16, 24) };
+    const off = registerNavigationProvider(async (view) => {
+      const at = view.state.doc.toString().indexOf("findName");
+      return { from: at, to: at + 8, targets: [xml] };
+    });
+    try {
+      // The syntax tree puts the caret on the method's name; the host then answers both.
+      cmd.syntaxNodeAt.mockReturnValueOnce(
+        ok({
+          node: node("identifier", r(3, 11, 19), "name"),
+          ancestors: [node("method_declaration", { start: { line: 3, col: 4 }, end: { line: 3, col: 29 } })],
+        }),
+      );
+      cmd.lspGoto.mockReturnValueOnce(ok([xml, { path: "/p/UserMapper.java", range: r(3, 11, 19) }]));
+      const view = editor(
+        "package demo;\n\npublic interface UserMapper {\n    String findName(Long id);\n}\n",
+        "java",
+        58,
+        "/p/UserMapper.java",
+      );
+      await gotoTargets(view, "definition");
+      expect(executeAction).toHaveBeenCalledWith("find.showUsages");
+      expect(openFile).not.toHaveBeenCalled();
+
+      // A call: the plugin's link is followed without asking the language server.
+      executeAction.mockClear();
+      cmd.lspGoto.mockClear();
+      cmd.syntaxNodeAt.mockReturnValueOnce(
+        ok({ node: node("identifier", r(1, 26, 34), "name"), ancestors: [node("method_invocation", r(1, 24, 38))] }),
+      );
+      const call = editor("class S {\n  void f(UserMapper m) { m.findName(1L); }\n}\n", "java", 37, "/p/S.java");
+      await gotoTargets(call, "definition");
+      expect(openFile).toHaveBeenCalledWith("/p/UserMapper.xml", expect.objectContaining({ focus: true }));
+      expect(executeAction).not.toHaveBeenCalledWith("find.showUsages");
+      expect(cmd.lspGoto).not.toHaveBeenCalled();
+    } finally {
+      off();
+    }
+  });
+
   it("looks past a server answer that points at the import itself", async () => {
     cmd.lspGoto.mockReturnValueOnce(ok([{ path: "/p/a.py", range: r(0, 37, 43) }]));
     cmd.navIndexDefinitions.mockReturnValueOnce(ok([sym("logger", "variable", "/deps/torchtitan/tools/logging.py")]));

src/editor/lsp/syntaxFallback.ts

@@ -63,6 +63,14 @@ export function usageRole(at: NodeAt | null): UsageRole {
   return "other";
 }
 
+const DECLARATION = /(declaration|definition|declarator)$/;
+
+/** Whether the syntax tree puts the identifier at `at` as the name of a declaration (`int f()`'s `f`). */
+export function isDeclarationName(at: NodeAt | null): boolean {
+  const parent = at?.ancestors[0];
+  return !!parent && at.node.field === "name" && DECLARATION.test(parent.kind);
+}
+
 /** Index symbols that may be the declaration of `name` used in `role`. */
 export function filterSymbols(matches: readonly SymbolMatch[], name: string, role: UsageRole): SymbolMatch[] {
   return matches.filter((m) => {