Reland "[clang-tidy] fix bugprone-narrowing-conversions false positive for conditional expression" (#151874)

This is another attempt to merge previously
[reverted](#139474 (comment))
PR #139474. The added tests
`narrowing-conversions-conditional-expressions.c[pp]` failed on
[different (non x86_64)
platforms](#139474 (comment))
because the expected warning is implementation-defined. That's why the
test must explicitly specify target (the line `// RUN: -- -target
x86_64-unknown-linux`).

Author: AndreyG

clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp

@@ -555,15 +555,22 @@ bool NarrowingConversionsCheck::handleConditionalOperator(
     // We have an expression like so: `output = cond ? lhs : rhs`
     // From the point of view of narrowing conversion we treat it as two
     // expressions `output = lhs` and `output = rhs`.
-    handleBinaryOperator(Context, CO->getLHS()->getExprLoc(), Lhs,
-                         *CO->getLHS());
-    handleBinaryOperator(Context, CO->getRHS()->getExprLoc(), Lhs,
-                         *CO->getRHS());
+    handleConditionalOperatorArgument(Context, Lhs, CO->getLHS());
+    handleConditionalOperatorArgument(Context, Lhs, CO->getRHS());
     return true;
   }
   return false;
 }
 
+void NarrowingConversionsCheck::handleConditionalOperatorArgument(
+    const ASTContext &Context, const Expr &Lhs, const Expr *Arg) {
+  if (const auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(Arg))
+    if (!Arg->getIntegerConstantExpr(Context))
+      Arg = ICE->getSubExpr();
+
+  handleBinaryOperator(Context, Arg->getExprLoc(), Lhs, *Arg);
+}
+
 void NarrowingConversionsCheck::handleImplicitCast(
     const ASTContext &Context, const ImplicitCastExpr &Cast) {
   if (Cast.getExprLoc().isMacroID())

clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.h

@@ -85,6 +85,8 @@ class NarrowingConversionsCheck : public ClangTidyCheck {
   bool handleConditionalOperator(const ASTContext &Context, const Expr &Lhs,
                                  const Expr &Rhs);
 
+  void handleConditionalOperatorArgument(const ASTContext &Context,
+                                         const Expr &Lhs, const Expr *Arg);
   void handleImplicitCast(const ASTContext &Context,
                           const ImplicitCastExpr &Cast);
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -134,6 +134,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/infinite-loop>` check by adding detection for
   variables introduced by structured bindings.
 
+- Improved :doc:`bugprone-narrowing-conversions
+  <clang-tidy/checks/bugprone/narrowing-conversions>` check by fixing
+  false positive from analysis of a conditional expression in C.
+
 - Improved :doc:`bugprone-reserved-identifier
   <clang-tidy/checks/bugprone/reserved-identifier>` check by ignoring
   declarations in system headers.

clang-tools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c

@@ -0,0 +1,22 @@
+// RUN: %check_clang_tidy %s bugprone-narrowing-conversions %t -- \
+// RUN: -- -target x86_64-unknown-linux
+
+char test_char(int cond, char c) {
+	char ret = cond > 0 ? ':' : c;
+	return ret;
+}
+
+short test_short(int cond, short s) {
+	short ret = cond > 0 ? ':' : s;
+	return ret;
+}
+
+int test_int(int cond, int i) {
+	int ret = cond > 0 ? ':' : i;
+	return ret;
+}
+
+void test(int cond, int i) {
+  char x = cond > 0 ? ':' : i;
+  // CHECK-MESSAGES: :[[@LINE-1]]:29: warning: narrowing conversion from 'int' to signed type 'char' is implementation-defined [bugprone-narrowing-conversions]
+}

clang-tools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.cpp

@@ -0,0 +1,22 @@
+// RUN: %check_clang_tidy %s bugprone-narrowing-conversions %t -- \
+// RUN: -- -target x86_64-unknown-linux
+
+char test_char(int cond, char c) {
+	char ret = cond > 0 ? ':' : c;
+	return ret;
+}
+
+short test_short(int cond, short s) {
+	short ret = cond > 0 ? ':' : s;
+	return ret;
+}
+
+int test_int(int cond, int i) {
+	int ret = cond > 0 ? ':' : i;
+	return ret;
+}
+
+void test(int cond, int i) {
+  char x = cond > 0 ? ':' : i;
+  // CHECK-MESSAGES: :[[@LINE-1]]:29: warning: narrowing conversion from 'int' to signed type 'char' is implementation-defined [bugprone-narrowing-conversions]
+}