[clang-tidy] Fix altera-struct-pack-align crash for struct fields with incomplete type

[jubnzv]

Summary

We can only use ASTContext::getTypeInfo for complete types.

This fixes the following bugzilla issue: https://bugs.llvm.org/show_bug.cgi?id=50313.

[aaron.ballman]

LGTM, thank you for the fix!

clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp

void StructPackAlignCheck::check(const MatchFinder::MatchResult &Result) {
 
   // Get sizing info for the struct.
   llvm::SmallVector<std::pair<unsigned int, unsigned int>, 10> FieldSizes;
   unsigned int TotalBitSize = 0;
   for (const FieldDecl *StructField : Struct->fields()) {
     // For each StructField, record how big it is (in bits).
     // Would be good to use a pair of <offset, size> to advise a better
     // packing order.
+    QualType StructFieldTy = StructField->getType();
+    if (StructFieldTy->isIncompleteType())
+      return;
     unsigned int StructFieldWidth =
-        (unsigned int)Result.Context
-            ->getTypeInfo(StructField->getType().getTypePtr())
+        (unsigned int)Result.Context->getTypeInfo(StructFieldTy.getTypePtr())
             .Width;
     FieldSizes.emplace_back(StructFieldWidth, StructField->getFieldIndex());
     // FIXME: Recommend a reorganization of the struct (sort by StructField
     // size, largest to smallest).
     TotalBitSize += StructFieldWidth;
   }
 
   uint64_t CharSize = Result.Context->getCharWidth();

clang-tools-extra/test/clang-tidy/checkers/altera-struct-pack-align-no-crash.cpp

+// RUN: %check_clang_tidy -expect-clang-tidy-error %s altera-struct-pack-align %t -- -header-filter=.*
+
+struct A;
+struct B {
+  A a;
+// CHECK-MESSAGES: :[[@LINE-1]]:5: error: field has incomplete type 'A' [clang-diagnostic-error]
+};