From 416a22c585950abd672182aaf850f62c4a198457 Mon Sep 17 00:00:00 2001
From: Francois Berder <fberder@outlook.fr>
Date: Mon, 13 Apr 2026 15:29:45 +0200
Subject: [PATCH] Fix #8192: FN condition always false in for loop condition

When a for loop's condition is impossible given the initial value (e.g.
`for (int i = 0; i > 10; i++)`), cppcheck was not emitting a
knownConditionTrueFalse warning.

Fix by populating memory1, memory2 and memoryAfter with the init state
when the condition is immediately false (and no error occured). We can
then set the value for the condition token and thus emit a
knownConditionTrueFalse warning.

Signed-off-by: Francois Berder <fberder@outlook.fr>
---
 lib/valueflow.cpp      | 55 ++++++++++++++++++++++++++++--------------
 test/testcondition.cpp |  2 +-
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/lib/valueflow.cpp b/lib/valueflow.cpp
index 3819bfc4b41..a63995a9728 100644
--- a/lib/valueflow.cpp
+++ b/lib/valueflow.cpp
@@ -5181,8 +5181,18 @@ static bool valueFlowForLoop2(const Token *tok,
     if (error)
         return false;
     execute(secondExpression, programMemory, &result, &error, settings);
-    if (result == 0) // 2nd expression is false => no looping
+    if (result == 0) {
+        if (!error) { // 2nd expression is false => no looping
+            ProgramMemory startMemory(programMemory);
+            ProgramMemory endMemory(programMemory);
+
+            memory1.swap(startMemory);
+            memory2.swap(endMemory);
+            memoryAfter.swap(programMemory);
+            return true;
+        }
         return false;
+    }
     if (error) {
         // If a variable is reassigned in second expression, return false
         bool reassign = false;
@@ -5388,23 +5398,32 @@ static void valueFlowForLoop(const TokenList &tokenlist, const SymbolDatabase& s
         } else {
             ProgramMemory mem1, mem2, memAfter;
             if (valueFlowForLoop2(tok, mem1, mem2, memAfter, settings)) {
-                for (const auto& p : mem1) {
-                    if (!p.second.isIntValue())
-                        continue;
-                    if (p.second.isImpossible())
-                        continue;
-                    if (p.first.tok->varId() == 0)
-                        continue;
-                    valueFlowForLoopSimplify(bodyStart, p.first.tok, false, p.second.intvalue, tokenlist, errorLogger, settings);
-                }
-                for (const auto& p : mem2) {
-                    if (!p.second.isIntValue())
-                        continue;
-                    if (p.second.isImpossible())
-                        continue;
-                    if (p.first.tok->varId() == 0)
-                        continue;
-                    valueFlowForLoopSimplify(bodyStart, p.first.tok, false, p.second.intvalue, tokenlist, errorLogger, settings);
+                if (mem1 == memAfter) { // #8192 check if loop never runs
+                    Token* condTok = getCondTok(tok);
+                    if (condTok && !condTok->hasKnownIntValue()) {
+                        ValueFlow::Value v(0);
+                        v.setKnown();
+                        ValueFlow::setTokenValue(condTok, std::move(v), settings);
+                    }
+                } else {
+                    for (const auto& p : mem1) {
+                        if (!p.second.isIntValue())
+                            continue;
+                        if (p.second.isImpossible())
+                            continue;
+                        if (p.first.tok->varId() == 0)
+                            continue;
+                        valueFlowForLoopSimplify(bodyStart, p.first.tok, false, p.second.intvalue, tokenlist, errorLogger, settings);
+                    }
+                    for (const auto& p : mem2) {
+                        if (!p.second.isIntValue())
+                            continue;
+                        if (p.second.isImpossible())
+                            continue;
+                        if (p.first.tok->varId() == 0)
+                            continue;
+                        valueFlowForLoopSimplify(bodyStart, p.first.tok, false, p.second.intvalue, tokenlist, errorLogger, settings);
+                    }
                 }
                 for (const auto& p : memAfter) {
                     if (!p.second.isIntValue())
diff --git a/test/testcondition.cpp b/test/testcondition.cpp
index 8172f74aab6..46860d9f939 100644
--- a/test/testcondition.cpp
+++ b/test/testcondition.cpp
@@ -5680,7 +5680,7 @@ class TestCondition : public TestFixture {
         check("void f() {\n" // #8192
               "    for (int i = 0; i > 10; ++i) {}\n"
               "}\n");
-        TODO_ASSERT_EQUALS("[test.cpp:2]: (style) Condition 'i>10' is always false\n", "", errout_str());
+        ASSERT_EQUALS("[test.cpp:2:23]: (style) Condition 'i>10' is always false [knownConditionTrueFalse]\n", errout_str());
 
         check("void f() {\n"
               "    for (int i = 1000; i < 20; ++i) {}\n"