Fix issue 10214: FP: danglingTempReference doesn't account for reference lifetime extension (#3220)

* Fix issue 10214: FP: danglingTempReference doesn't account for reference lifetime extension

lib/checkautovariables.cpp

@@ -488,6 +488,18 @@ static bool isDanglingSubFunction(const Token* tokvalue, const Token* tok)
     return exprDependsOnThis(parent);
 }
 
+static bool isAssignedToNonLocal(const Token* tok)
+{
+    if (!Token::simpleMatch(tok->astParent(), "="))
+        return false;
+    if (!Token::Match(tok->astParent()->astOperand1(), "%var%"))
+        return false;
+    const Variable* var = tok->astParent()->astOperand1()->variable();
+    if (!var)
+        return false;
+    return !var->isLocal() || var->isStatic();
+}
+
 void CheckAutoVariables::checkVarLifetimeScope(const Token * start, const Token * end)
 {
     const bool printInconclusive = mSettings->certainty.isEnabled(Certainty::inconclusive);
@@ -546,7 +558,8 @@ void CheckAutoVariables::checkVarLifetimeScope(const Token * start, const Token
             if (!printInconclusive && val.isInconclusive())
                 continue;
             const bool escape = Token::Match(tok->astParent(), "return|throw");
-            for (const LifetimeToken& lt : getLifetimeTokens(getParentLifetime(val.tokvalue), escape)) {
+            for (const LifetimeToken& lt :
+                 getLifetimeTokens(getParentLifetime(val.tokvalue), escape || isAssignedToNonLocal(tok))) {
                 const Token * tokvalue = lt.token;
                 if (val.isLocalLifetimeValue()) {
                     if (escape) {

lib/valueflow.cpp

@@ -2693,10 +2693,10 @@ std::vector<LifetimeToken> getLifetimeTokens(const Token* tok, bool escape, Valu
             } else if (Token::simpleMatch(var->declEndToken(), "=")) {
                 errorPath.emplace_back(var->declEndToken(), "Assigned to reference.");
                 const Token *vartok = var->declEndToken()->astOperand2();
-                const bool temporaryDefault = false; //If we can't tell then assume the value is not temporary as this will result in fewer false positives.
+                const bool temporary = isTemporary(true, vartok, nullptr, true);
-                const bool temporary = isTemporary(true, vartok, nullptr, temporaryDefault);
                 const bool nonlocal = var->isStatic() || var->isGlobal();
-                if (vartok == tok || (nonlocal && temporary) || (!escape && (var->isConst() || var->isRValueReference()) && temporary))
+                if (vartok == tok || (nonlocal && temporary) ||
+                    (!escape && (var->isConst() || var->isRValueReference()) && temporary))
                     return {{tok, true, std::move(errorPath)}};
                 if (vartok)
                     return getLifetimeTokens(vartok, escape, std::move(errorPath), depth - 1);

test/testautovariables.cpp

@@ -2597,6 +2597,19 @@ private:
               "    return e;\n"
               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        // #10214
+        check("struct A {\n"
+              "  std::string key;\n"
+              "  const char *value;\n"
+              "};\n"
+              "const char *f(const std::string &key, const std::vector<A> &lookup) {\n"
+              "  const auto &entry =\n"
+              "      std::find_if(lookup.begin(), lookup.end(),\n"
+              "                   [key](const auto &v) { return v.key == key; });\n"
+              "  return (entry == lookup.end()) ? \"\" : entry->value;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void danglingLifetimeFunction() {