[clang] Fix crash 'Cannot get layout of forward declarations' during CTU static analysis (#156056)

When a type is imported with `ASTImporter`, the "original declaration"
of the type is imported. In some cases this is not the definition
(of the class). Before the fix the definition was only imported if
there was an other reference to it in the AST to import. This is not
always the case (like in the added test case), if not the definition
was missing in the "To" AST which can cause the assertion later.

Author: balazske

clang/lib/AST/ASTImporter.cpp

@@ -1740,10 +1740,21 @@ ExpectedType ASTNodeImporter::VisitDeducedTemplateSpecializationType(
 }
 
 ExpectedType ASTNodeImporter::VisitTagType(const TagType *T) {
-  Expected<TagDecl *> ToDeclOrErr = import(T->getOriginalDecl());
+  TagDecl *DeclForType = T->getOriginalDecl();
+  Expected<TagDecl *> ToDeclOrErr = import(DeclForType);
   if (!ToDeclOrErr)
     return ToDeclOrErr.takeError();
 
+  if (DeclForType->isUsed()) {
+    // If there is a definition of the 'OriginalDecl', it should be imported to
+    // have all information for the type in the "To" AST. (In some cases no
+    // other reference may exist to the definition decl and it would not be
+    // imported otherwise.)
+    Expected<TagDecl *> ToDefDeclOrErr = import(DeclForType->getDefinition());
+    if (!ToDefDeclOrErr)
+      return ToDefDeclOrErr.takeError();
+  }
+
   if (T->isCanonicalUnqualified())
     return Importer.getToContext().getCanonicalTagType(*ToDeclOrErr);
 

clang/test/Analysis/ctu-import-type-decl-definition.c

@@ -0,0 +1,43 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -emit-pch -o %t/import.c.ast %t/import.c
+
+// RUN: %clang_extdef_map -- -x c %t/import.c >> %t/externalDefMap.txt
+// RUN: sed -i='' 's/$/.ast/' %t/externalDefMap.txt
+
+// RUN: %clang_cc1 -analyze \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-config experimental-enable-naive-ctu-analysis=true \
+// RUN:   -analyzer-config display-ctu-progress=true \
+// RUN:   -analyzer-config ctu-dir=%t \
+// RUN:   -verify %t/main.c
+
+//--- main.c
+
+// expected-no-diagnostics
+
+typedef struct X_s X_t;
+unsigned long f_import(struct X_s *xPtr);
+
+static void freeWriteFileResources(struct X_s *xPtr) {
+  f_import(xPtr);
+}
+
+//--- import.c
+
+typedef struct Y_s Y_t;
+
+struct Y_s {
+};
+
+struct X_s {
+  Y_t y;
+};
+
+unsigned long f_import(struct X_s *xPtr) {
+  if (xPtr != 0) {
+  }
+  return 0;
+}