Warn on dangling comparison operator. (#2779)

Fixes #1685

Co-authored-by: Yong He <yhe@nvidia.com>

2 files changed, 11 insertions, 0 deletions

diff --git a/source/slang/slang-check-stmt.cpp b/source/slang/slang-check-stmt.cpp
index a61f48af6..6efc3e52e 100644
--- a/source/slang/slang-check-stmt.cpp
+++ b/source/slang/slang-check-stmt.cpp
@@ -339,6 +339,16 @@ namespace Slang
     void SemanticsStmtVisitor::visitExpressionStmt(ExpressionStmt *stmt)
     {
         stmt->expression = CheckExpr(stmt->expression);
+        if (auto operatorExpr = as<OperatorExpr>(stmt->expression))
+        {
+            if (auto func = as<VarExpr>(operatorExpr->functionExpr))
+            {
+                if (func->name && func->name->text == "==")
+                {
+                    getSink()->diagnose(operatorExpr, Diagnostics::danglingEqualityExpr);
+                }
+            }
+        }
     }
 
     void SemanticsStmtVisitor::tryInferLoopMaxIterations(ForStmt* stmt)
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index fed4944d3..4a9b83c6c 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -278,6 +278,7 @@ DIAGNOSTIC(30054, Error, targetLabelDoesNotMarkBreakableStmt, "invalid break tar
 DIAGNOSTIC(30055, Error, useOfNonShortCircuitingOperatorInDiffFunc, "non-short-circuiting `?:` operator is not allowed in a differentiable function, use `select` instead.")
 DIAGNOSTIC(30056, Warning, useOfNonShortCircuitingOperator, "non-short-circuiting `?:` operator is deprecated, use 'select' instead.")
 DIAGNOSTIC(30057, Error, assignmentInPredicateExpr, "use an assignment operation as predicate expression is not allowed, wrap the assignment with '()' to clarify the intent.")
+DIAGNOSTIC(30058, Warning, danglingEqualityExpr, "result of '==' not used, did you intend '='?")
 
 DIAGNOSTIC(30043, Error, getStringHashRequiresStringLiteral, "getStringHash parameter can only accept a string literal")