llvm · AmrDeveloper · Mar 6, 2025 · Feb 28, 2025 · Mar 3, 2025 · Mar 5, 2025
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -220,6 +220,8 @@ Improvements to Clang's diagnostics
   :doc:`ThreadSafetyAnalysis` still does not perform alias analysis. The
   feature will be default-enabled with ``-Wthread-safety`` in a future release.
 
+- Improve the diagnostics for chained comparisons to report actual expressions and operators (#GH129069).
+
 - Improve the diagnostics for shadows template parameter to report correct location (#GH129060).
 
 Improvements to Clang's time-trace

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7157,7 +7157,7 @@ def note_precedence_conditional_first : Note<
   "place parentheses around the '?:' expression to evaluate it first">;
 
 def warn_consecutive_comparison : Warning<
-  "comparisons like 'X<=Y<=Z' don't have their mathematical meaning">,
+  "chained comparison 'X %0 Y %1 Z' does not behave the same as a mathematical expression">,
   InGroup<Parentheses>, DefaultError;
 
 def warn_enum_constant_in_bool_context : Warning<

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
@@ -14924,7 +14924,8 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
 
     if (const auto *BI = dyn_cast<BinaryOperator>(LHSExpr);
         BI && BI->isComparisonOp())
-      Diag(OpLoc, diag::warn_consecutive_comparison);
+      Diag(OpLoc, diag::warn_consecutive_comparison)
+          << BI->getOpcodeStr() << BinaryOperator::getOpcodeStr(Opc);
 
     break;
   case BO_EQ:

diff --git a/clang/test/Sema/bool-compare.c b/clang/test/Sema/bool-compare.c
@@ -85,7 +85,7 @@ void f(int x, int y, int z) {
   if ((a<y) != -1) {}// expected-warning {{comparison of constant -1 with boolean expression is always true}}
 
   if ((a<y) == z) {} // no warning
-  if (a>y<z)      {} // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  if (a>y<z)      {} // expected-error {{chained comparison 'X > Y < Z' does not behave the same as a mathematical expression}}
   if ((a<y) > z)  {} // no warning
   if((a<y)>(z<y)) {} // no warning
   if((a<y)==(z<y)){} // no warning
@@ -145,7 +145,7 @@ void f(int x, int y, int z) {
   if (-1 !=(a<y)) {} // expected-warning {{comparison of constant -1 with boolean expression is always true}}
 
   if (z ==(a<y))  {}    // no warning
-  if (z<a>y)      {} // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  if (z<a>y)      {} // expected-error {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
   if (z > (a<y))  {}    // no warning
   if((z<y)>(a<y)) {}   // no warning
   if((z<y)==(a<y)){}  // no warning

diff --git a/clang/test/Sema/parentheses.cpp b/clang/test/Sema/parentheses.cpp
@@ -217,10 +217,10 @@ namespace PR20735 {
 }
 
 void consecutive_builtin_compare(int x, int y, int z) {
-  (void)(x < y < z);  // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
-  (void)(x < y > z);  // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
-  (void)(x < y <= z); // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
-  (void)(x <= y > z); // expected-warning {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  (void)(x < y < z);  // expected-warning {{chained comparison 'X < Y < Z' does not behave the same as a mathematical expression}}
+  (void)(x < y > z);  // expected-warning {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
+  (void)(x < y <= z); // expected-warning {{chained comparison 'X < Y <= Z' does not behave the same as a mathematical expression}}
+  (void)(x <= y > z); // expected-warning {{chained comparison 'X <= Y > Z' does not behave the same as a mathematical expression}}
   (void)((x < y) < z);  // no-warning
   (void)((x < y) >= z); // no-warning
 

diff --git a/clang/test/SemaCXX/bool-compare.cpp b/clang/test/SemaCXX/bool-compare.cpp
@@ -98,7 +98,7 @@ void f(int x, int y, int z) {
   if ((a<y) != -1) {}// expected-warning {{comparison of constant -1 with expression of type 'bool' is always true}}
 
   if ((a<y) == z) {} // no warning
-  if (a>y<z)      {} // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  if (a>y<z)      {} // expected-error {{chained comparison 'X > Y < Z' does not behave the same as a mathematical expression}}
   if ((a<y) > z)  {} // no warning
   if((a<y)>(z<y)) {} // no warning
   if((a<y)==(z<y)){} // no warning
@@ -159,7 +159,7 @@ void f(int x, int y, int z) {
   if (-1 !=(a<y)) {} // expected-warning {{comparison of constant -1 with expression of type 'bool' is always true}}
 
   if (z ==(a<y))  {} // no warning
-  if (z<a>y)      {} // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  if (z<a>y)      {} // expected-error {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
   if (z > (a<y))  {} // no warning
   if((z<y)>(a<y)) {} // no warning
   if((z<y)==(a<y)){} // no warning

diff --git a/clang/test/SemaCXX/cxx2a-adl-only-template-id.cpp b/clang/test/SemaCXX/cxx2a-adl-only-template-id.cpp
@@ -27,7 +27,7 @@ int e = h<0>(q); // ok, found by unqualified lookup
 void fn() {
   f<0>(q);
   int f;
-  f<0>(q); // expected-error {{invalid operands to binary expression}} // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+  f<0>(q); // expected-error {{invalid operands to binary expression}} // expected-error {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
 }
 
 void disambig() {

diff --git a/clang/test/SemaTemplate/typo-dependent-name.cpp b/clang/test/SemaTemplate/typo-dependent-name.cpp
@@ -20,7 +20,7 @@ struct X : Base<T> {
   bool f(T other) {
     // A pair of comparisons; 'inner' is a dependent name so can't be assumed
     // to be a template.
-    return this->inner < other > ::z; // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+    return this->inner < other > ::z; // expected-error {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
   }
 };
 

diff --git a/clang/test/SemaTemplate/typo-template-name.cpp b/clang/test/SemaTemplate/typo-template-name.cpp
@@ -36,7 +36,7 @@ namespace InExpr {
 
     // These are valid expressions.
     foo<foo; // expected-warning {{self-comparison}}
-    foo<int()>(0); // expected-error {{comparisons like 'X<=Y<=Z' don't have their mathematical meaning}}
+    foo<int()>(0); // expected-error {{chained comparison 'X < Y > Z' does not behave the same as a mathematical expression}}
     foo<int(), true>(false);
     foo<Base{}.n;
   }