Partial fix for #12387 FP unsignedLessThanZero for template type (#5922)

Author: chrchr-github

lib/checkcondition.cpp

@@ -1567,7 +1567,7 @@ void CheckCondition::alwaysTrueFalse()
             {
                 const ValueFlow::Value *zeroValue = nullptr;
                 const Token *nonZeroExpr = nullptr;
-                if (CheckOther::comparisonNonZeroExpressionLessThanZero(tok, &zeroValue, &nonZeroExpr) ||
+                if (CheckOther::comparisonNonZeroExpressionLessThanZero(tok, &zeroValue, &nonZeroExpr, /*suppress*/ true) ||
                     CheckOther::testIfNonZeroExpressionIsPositive(tok, &zeroValue, &nonZeroExpr))
                     continue;
             }

lib/checkother.cpp

@@ -2737,7 +2737,7 @@ void CheckOther::checkSignOfUnsignedVariable()
     }
 }
 
-bool CheckOther::comparisonNonZeroExpressionLessThanZero(const Token *tok, const ValueFlow::Value **zeroValue, const Token **nonZeroExpr)
+bool CheckOther::comparisonNonZeroExpressionLessThanZero(const Token *tok, const ValueFlow::Value **zeroValue, const Token **nonZeroExpr, bool suppress)
 {
     if (!tok->isComparisonOp() || !tok->astOperand1() || !tok->astOperand2())
         return false;
@@ -2755,6 +2755,10 @@ bool CheckOther::comparisonNonZeroExpressionLessThanZero(const Token *tok, const
         return false;
     }
 
+    if (const Variable* var = (*nonZeroExpr)->variable())
+        if (var->typeStartToken()->isTemplateArg())
+            return suppress;
+
     const ValueType* vt = (*nonZeroExpr)->valueType();
     return vt && (vt->pointer || vt->sign == ValueType::UNSIGNED);
 }

lib/checkother.h

@@ -56,7 +56,7 @@ class CPPCHECKLIB CheckOther : public Check {
     CheckOther() : Check(myName()) {}
 
     /** Is expression a comparison that checks if a nonzero (unsigned/pointer) expression is less than zero? */
-    static bool comparisonNonZeroExpressionLessThanZero(const Token *tok, const ValueFlow::Value **zeroValue, const Token **nonZeroExpr);
+    static bool comparisonNonZeroExpressionLessThanZero(const Token *tok, const ValueFlow::Value **zeroValue, const Token **nonZeroExpr, bool suppress = false);
 
     /** Is expression a comparison that checks if a nonzero (unsigned/pointer) expression is positive? */
     static bool testIfNonZeroExpressionIsPositive(const Token *tok, const ValueFlow::Value **zeroValue, const Token **nonZeroExpr);

test/testother.cpp

@@ -8250,6 +8250,18 @@ class TestOther : public TestFixture {
               "   if (y < x) {}\n"
               "}");
         ASSERT_EQUALS("[test.cpp:4]: (style) Checking if unsigned expression 'y' is less than zero.\n", errout.str());
+
+        // #12387
+        check("template<typename T>\n"
+              "void f(T t) {\n"
+              "    if constexpr (std::numeric_limits<T>::is_signed) {\n"
+              "        if (t < 0) {}\n"
+              "    }\n"
+              "}\n"
+              "void g() {\n"
+              "    f<uint32_t>(0);\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void checkSignOfPointer() {