[clang] Do not crash in APValue::prettyPrint() on forward-decl structs.

[adamcz]

Summary

The call to getTypeSizeInChars() is replaced with
getTypeSizeInCharsIfKnown(), which does not crash on forward declared
structs. This only affects printing.

[hokein]

Thanks!

clang-tools-extra/clangd/unittests/HoverTests.cpp

TEST(Hover, SpaceshipTemplateNoCrash) {
 
   TestTU TU = TestTU::withCode(T.code());
   TU.ExtraArgs.push_back("-std=c++20");
   auto AST = TU.build();
   auto HI = getHover(AST, T.point(), format::getLLVMStyle(), nullptr);
   EXPECT_EQ(HI->Documentation, "Foo bar baz");
 }
 
+TEST(Hover, ForwardStructNoCrash) {
+  Annotations T(R"cpp(
+  struct Foo;
+  int bar;
+  auto baz = (Fo^o*)&bar;
+    )cpp");
+
+  TestTU TU = TestTU::withCode(T.code());
+  auto AST = TU.build();
+  auto HI = getHover(AST, T.point(), format::getLLVMStyle(), nullptr);
+  ASSERT_TRUE(HI);
+  EXPECT_EQ(*HI->Value, "&bar");
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang

clang/lib/AST/APValue.cpp

if (!Base) {
             << getLValueOffset().getQuantity();
       }
       return;
     }
 
     if (!hasLValuePath()) {
       // No lvalue path: just print the offset.
       CharUnits O = getLValueOffset();
-      CharUnits S = Ctx ? Ctx->getTypeSizeInChars(InnerTy) : CharUnits::Zero();
+      CharUnits S = Ctx ? Ctx->getTypeSizeInCharsIfKnown(InnerTy).getValueOr(
+                              CharUnits::Zero())
+                        : CharUnits::Zero();
       if (!O.isZero()) {
         if (IsReference)
           Out << "*(";
         if (S.isZero() || O % S) {
           Out << "(char*)";
           S = CharUnits::One();
         }
         Out << '&';