[clang-tidy] fix false-positive for cppcoreguidelines-pro-type-member-init with in-class initializers

[mgehre]

Summary

This fixes https://llvm.org/bugs/show_bug.cgi?id=30487 where

warning: uninitialized record type: 's' [cppcoreguidelines-pro-type-member-init]

is emitted on

struct MyStruct
{
    int a = 5;
    int b = 7;
};

int main()
{
    MyStruct s;
}

[malcolm.parsons]

test/clang-tidy/cppcoreguidelines-pro-type-member-init.cpp

372

There's already this test:

struct NegativeInClassInitialized {
    int F = 0;  
    NegativeInClassInitialized() {}
};

I'd call your test NegativeInClassInitializedImplicit, and also add this:

struct NegativeInClassInitializedDefaulted {
    int F = 0;
    NegativeInClassInitializedDefaulted() = default;
};

[aaron.ballman]

LGTM with Malcom's test suggestions addressed.

[mgehre]

Rename the struct that was introduced in the test. Note that I need to keep the function Bug30487,
because that is where the false-positive warning was emitted.

[malcolm.parsons]

In D24848#554145, @mgehre wrote:

Rename the struct that was introduced in the test. Note that I need to keep the function Bug30487,
because that is where the false-positive warning was emitted.

D24965 will allow you to write a positive test instead:

struct PositivePartiallyInClassInitialized {
  // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: constructor does not initialize these fields: G
  int F = 0;
  int G;
  // CHECK-FIXES: int G{};
};

[mgehre]

I would like to close that particular bug report, and thus I would like to have the reproducer of that bug as part of the test case.
The PositivePartiallyInClassInitialized is also a good test, but I fail to see how it is proves that that particular bug is solved.

Are you okay with me committing this as it currently is?

[malcolm.parsons]

In D24848#555636, @mgehre wrote:

Are you okay with me committing this as it currently is?

Yes.

clang-tidy/utils/TypeTraits.cpp

bool recordIsTriviallyDefaultConstructible(const RecordDecl &RecordDecl,
   // A class with a user-provided default constructor is not trivially
   // constructible.
   if (ClassDecl->hasUserProvidedDefaultConstructor())
     return false;
   // A class is trivially constructible if it has a trivial default constructor.
   if (ClassDecl->hasTrivialDefaultConstructor())
     return true;
 
-  // If all its fields are trivially constructible.
+  // If all its fields are trivially constructible and have no default initializers.
   for (const FieldDecl *Field : ClassDecl->fields()) {
+    if (Field->hasInClassInitializer())
+      return false;
     if (!isTriviallyDefaultConstructible(Field->getType(), Context))
       return false;
   }
   // If all its direct bases are trivially constructible.
   for (const CXXBaseSpecifier &Base : ClassDecl->bases()) {
     if (!isTriviallyDefaultConstructible(Base.getType(), Context))
       return false;
   }

test/clang-tidy/cppcoreguidelines-pro-type-member-init.cpp

class PositiveIndirectMember {
   struct {
     int *A;
     // CHECK-FIXES: int *A{};
   };
 
   PositiveIndirectMember() {}
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: constructor does not initialize these fields: A
 };
+
+
+struct Bug30487
+{
+  int a = 0;
+};
+
+void Bug30487_f()
+{
+  Bug30487 s;
+}