[clang] Skip implicit designators in DesignatedInitExpr::getBeginLoc (#83369)

Fixes #83185

Author: alirezamoshtaghi

clang-tools-extra/clangd/unittests/tweaks/ExtractVariableTests.cpp

@@ -72,6 +72,22 @@ TEST_F(ExtractVariableTest, Test) {
     )cpp";
   EXPECT_UNAVAILABLE(NoCrashCasesC);
 
+  ExtraArgs = {"-xc"};
+  const char *NoCrashDesignator = R"cpp(
+    struct A {
+      struct {
+        int x;
+      };
+    };
+    struct B {
+      int y;
+    };
+    void foo(struct B *b) {
+      struct A a = {.x=b[[->]]y};
+    }
+  )cpp";
+  EXPECT_AVAILABLE(NoCrashDesignator);
+
   ExtraArgs = {"-xobjective-c"};
   const char *AvailableObjC = R"cpp(
     __attribute__((objc_root_class))

clang/lib/AST/Expr.cpp

@@ -4604,8 +4604,17 @@ SourceRange DesignatedInitExpr::getDesignatorsSourceRange() const {
 SourceLocation DesignatedInitExpr::getBeginLoc() const {
   auto *DIE = const_cast<DesignatedInitExpr *>(this);
   Designator &First = *DIE->getDesignator(0);
-  if (First.isFieldDesignator())
-    return GNUSyntax ? First.getFieldLoc() : First.getDotLoc();
+  if (First.isFieldDesignator()) {
+    // Skip past implicit designators for anonymous structs/unions, since
+    // these do not have valid source locations.
+    for (unsigned int i = 0; i < DIE->size(); i++) {
+      Designator &Des = *DIE->getDesignator(i);
+      SourceLocation retval = GNUSyntax ? Des.getFieldLoc() : Des.getDotLoc();
+      if (!retval.isValid())
+        continue;
+      return retval;
+    }
+  }
   return First.getLBracketLoc();
 }