[clang-tidy] detect explicit casting within modernize-use-default-member-init

[RiverDave]

This aims to fix a portion of #122480. Added some matchers to detect explicit casting which utilize builtin types as its source expression. these are the various forms of casting supported I thought would useful for this check:

• C Style explicit casting
• Static explicit casting
• Functional explicit casting

[llvmbot]

@llvm/pr-subscribers-clang-tidy

@llvm/pr-subscribers-clang-tools-extra

Author: David Rivera (RiverDave)

Changes

This aims to fix a portion of #122480. Added some matchers to detect explicit casting which utilize builtin types as its source expression. these are the various forms of casting supported I thought would useful for this check:

• C Style explicit casting
• Static explicit casting
• Functional explicit casting

---

Full diff: https://github.com/llvm/llvm-project/pull/129408.diff

3 Files Affected:

• (modified) clang-tools-extra/clang-tidy/modernize/UseDefaultMemberInitCheck.cpp (+20-9)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+4)
• (modified) clang-tools-extra/test/clang-tidy/checkers/modernize/use-default-member-init.cpp (+40)

diff --git a/clang-tools-extra/clang-tidy/modernize/UseDefaultMemberInitCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseDefaultMemberInitCheck.cpp
index 6c06b0af342f6..2d92d8ea601ed 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseDefaultMemberInitCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseDefaultMemberInitCheck.cpp
@@ -176,6 +176,11 @@ static bool sameValue(const Expr *E1, const Expr *E2) {
            cast<StringLiteral>(E2)->getString();
   case Stmt::DeclRefExprClass:
     return cast<DeclRefExpr>(E1)->getDecl() == cast<DeclRefExpr>(E2)->getDecl();
+  case Stmt::CStyleCastExprClass:
+  case Stmt::CXXStaticCastExprClass:
+  case Stmt::CXXFunctionalCastExprClass:
+    return sameValue(cast<ExplicitCastExpr>(E1)->getSubExpr(),
+                     cast<ExplicitCastExpr>(E2)->getSubExpr());
   default:
     return false;
   }
@@ -194,15 +199,21 @@ void UseDefaultMemberInitCheck::storeOptions(
 }
 
 void UseDefaultMemberInitCheck::registerMatchers(MatchFinder *Finder) {
-  auto InitBase =
-      anyOf(stringLiteral(), characterLiteral(), integerLiteral(),
-            unaryOperator(hasAnyOperatorName("+", "-"),
-                          hasUnaryOperand(integerLiteral())),
-            floatLiteral(),
-            unaryOperator(hasAnyOperatorName("+", "-"),
-                          hasUnaryOperand(floatLiteral())),
-            cxxBoolLiteral(), cxxNullPtrLiteralExpr(), implicitValueInitExpr(),
-            declRefExpr(to(enumConstantDecl())));
+
+  auto ExplicitCastExpr = castExpr(hasSourceExpression(anyOf(
+      unaryOperator(hasAnyOperatorName("+", "-"),
+                    hasUnaryOperand(anyOf(integerLiteral(), floatLiteral()))),
+      integerLiteral(), floatLiteral(), characterLiteral())));
+
+  auto InitBase = anyOf(
+      stringLiteral(), characterLiteral(), integerLiteral(), ExplicitCastExpr,
+      unaryOperator(hasAnyOperatorName("+", "-"),
+                    hasUnaryOperand(integerLiteral())),
+      floatLiteral(),
+      unaryOperator(hasAnyOperatorName("+", "-"),
+                    hasUnaryOperand(floatLiteral())),
+      cxxBoolLiteral(), cxxNullPtrLiteralExpr(), implicitValueInitExpr(),
+      declRefExpr(to(enumConstantDecl())));
 
   auto Init =
       anyOf(initListExpr(anyOf(allOf(initCountIs(1), hasInit(0, InitBase)),
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 07a79d6bbe807..330abf99ce8c9 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -128,6 +128,10 @@ Changes in existing checks
   <clang-tidy/checks/misc/redundant-expression>` check by providing additional
   examples and fixing some macro related false positives.
 
+- Improved :doc:`modernize-use-default-member-init
+  <clang-tidy/checks/modernize/use-default-member-init>` check by detecting
+  explicit casting of built-in types within member list initialization.
+
 - Improved :doc:`performance/unnecessary-value-param
   <clang-tidy/checks/performance/unnecessary-value-param>` check performance by
   tolerating fix-it breaking compilation when functions is used as pointers 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-default-member-init.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-default-member-init.cpp
index 81c980e0217e6..19a1d63bb9ec0 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-default-member-init.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-default-member-init.cpp
@@ -518,3 +518,43 @@ class ArrayBraceInitMultipleValues {
 };
 
 } // namespace PR63285
+
+namespace PR63285 {
+
+class CStyleCastInit {
+  CStyleCastInit() : a{(int)1.23}, b{(float)42}, c{(double)'C'} {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:50: warning: member initializer for 'c' is redundant [modernize-use-default-member-init]
+  // CHECK-FIXES: CStyleCastInit()  {}
+
+  int a;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use default member initializer for 'a' [modernize-use-default-member-init]
+  // CHECK-FIXES: int a{(int)1.23};
+  float b;
+  // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: use default member initializer for 'b' [modernize-use-default-member-init]
+  // CHECK-FIXES: float b{(float)42};
+  double c{(double)'C'};
+};
+
+class StaticCastInit {
+  StaticCastInit() : m(static_cast<int>(9.99)), n(static_cast<char>(65)) {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:49: warning: member initializer for 'n' is redundant [modernize-use-default-member-init]
+  // CHECK-FIXES: StaticCastInit()  {}
+  int m;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use default member initializer for 'm' [modernize-use-default-member-init]
+  // CHECK-FIXES: int m{static_cast<int>(9.99)};
+  char n{static_cast<char>(65)};
+};
+
+class FunctionalCastInit {
+  FunctionalCastInit() : a(int(5.67)), b(float(2)), c(double('C')) {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:40: warning: member initializer for 'b' is redundant [modernize-use-default-member-init]
+  int a;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use default member initializer for 'a' [modernize-use-default-member-init]
+  // CHECK-FIXES: int a{int(5.67)};
+  float b{float(2)};
+  double c;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use default member initializer for 'c' [modernize-use-default-member-init]
+  // CHECK-FIXES: double c{double('C')};
+};
+
+} //namespace PR63285
\ No newline at end of file

[RiverDave]

ping

[PiotrZSL]

Change looks correct, but looks like this check got one more limitation in case of code like this:

class CastInit {
  CastInit() : m(static_cast<int>(9)) {}
  int m = 9;
};

And this:

class CastInit {
  CastInit() : m(static_cast<int>(0)) {}
  int m {};
};

[RiverDave]

Change looks correct, but looks like this check got one more limitation in case of code like this:

class CastInit {
  CastInit() : m(static_cast<int>(9)) {}
  int m = 9;
};

And this:

class CastInit {
  CastInit() : m(static_cast<int>(0)) {}
  int m {};
};

Change looks correct, but looks like this check got one more limitation in case of code like this:

class CastInit {
  CastInit() : m(static_cast<int>(9)) {}
  int m = 9;
};

And this:

class CastInit {
  CastInit() : m(static_cast<int>(0)) {}
  int m {};
};

Hadn't thought of this, but your idea makes sense, I'll try to implement it.

[PiotrZSL]

@RiverDave If you rebase this change we can merge it, and then if you want you could work on next version in independent PR.

[RiverDave]

Ping