[clang] [Clang][Modules] Fix generic lambda local capture mapping mismatch in template instantiation (PR #202248)

[James Y Knight via cfe-commits]

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@@ -7421,3 +7421,67 @@ void Sema::PerformDependentDiagnostics(const DeclContext *Pattern,
     }
   }
 }
+
+static bool isMappedLocalDecl(const Decl *D) {
+  if (const auto *VD = dyn_cast<VarDecl>(D)) {
+    return VD->isLocalVarDeclOrParm() && !isa<ParmVarDecl>(VD);
+  }
+  return isa<BindingDecl>(D);
+}
+
+const Decl *Sema::getCanonicalLocalDecl(const Decl *D) {
+  if (isa<ParmVarDecl>(D)) {
+    return D;
+  }
+
+  const auto *VD = dyn_cast<VarDecl>(D);
+  const auto *BD = dyn_cast<BindingDecl>(D);
+  if (!VD && !BD) {
+    return D;
+  }
+
+  if (VD && !VD->isLocalVarDeclOrParm()) {
+    return D;
+  }
+
+  const DeclContext *DC = VD ? VD->getDeclContext() : BD->getDeclContext();
+  const auto *FD = dyn_cast<FunctionDecl>(DC);
+  if (!FD) {
+    return D;
+  }
+
+  const auto *CanonFD = FD->getCanonicalDecl();
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jyknight wrote:

We need the canonical _definition_, not just a decl, in order to be able to iterate `decls()` on it. Probably `FD->getDefinition()`? I think that's guaranteed to use return a canonical definition.

That'll end up with this using a different decl than the ParamVar mapping, which uses the  `getCanonicalDecl`. But maybe that's fine?

https://github.com/llvm/llvm-project/pull/202248