[clang-tidy] Fix crash in modernize-use-designated-initializers check (#113688)

Fix #113652.

When calling `Node.isAggregate()` and `Node.isPOD()`, if `Node` is declared but
not defined, it will result in null pointer dereference (and if assertions are
enabled, it will cause an assertion failure).

Author: z1nke

clang-tools-extra/clang-tidy/modernize/UseDesignatedInitializersCheck.cpp

@@ -80,9 +80,13 @@ unsigned getNumberOfDesignated(const InitListExpr *SyntacticInitList) {
   });
 }
 
-AST_MATCHER(CXXRecordDecl, isAggregate) { return Node.isAggregate(); }
+AST_MATCHER(CXXRecordDecl, isAggregate) {
+  return Node.hasDefinition() && Node.isAggregate();
+}
 
-AST_MATCHER(CXXRecordDecl, isPOD) { return Node.isPOD(); }
+AST_MATCHER(CXXRecordDecl, isPOD) {
+  return Node.hasDefinition() && Node.isPOD();
+}
 
 AST_MATCHER(InitListExpr, isFullyDesignated) {
   if (const InitListExpr *SyntacticForm =

clang-tools-extra/docs/ReleaseNotes.rst

@@ -216,6 +216,10 @@ Changes in existing checks
   a false positive when only an implicit conversion happened inside an
   initializer list.
 
+- Improved :doc:`modernize-use-designated-initializers
+  <clang-tidy/checks/modernize/use-designated-initializers>` check to fix a
+  crash when a class is declared but not defined.
+
 - Improved :doc:`modernize-use-nullptr
   <clang-tidy/checks/modernize/use-nullptr>` check to also recognize
   ``NULL``/``__null`` (but not ``0``) when used with a templated type.

clang-tools-extra/test/clang-tidy/checkers/modernize/use-designated-initializers.cpp

@@ -201,3 +201,11 @@ DECLARE_S93;
 // CHECK-MESSAGES-MACROS: :[[@LINE-1]]:1: warning: use designated initializer list to initialize 'S9' [modernize-use-designated-initializers]
 // CHECK-MESSAGES-MACROS: :[[@LINE-4]]:28: note: expanded from macro 'DECLARE_S93'
 // CHECK-MESSAGES-MACROS: :[[@LINE-71]]:1: note: aggregate type is defined here
+
+// Issue #113652.
+struct S14;
+
+struct S15{
+  S15(S14& d):d{d}{}
+  S14& d;
+};