Fix issue 9587: False positive: parameter can be declared with const (#2667)

lib/astutils.cpp

@@ -344,6 +344,22 @@ const Token* getParentMember(const Token * tok)
     return tok;
 }
 
+const Token* getParentLifetime(const Token* tok)
+{
+    if (!tok)
+        return tok;
+    const Variable* var = tok->variable();
+    // TODO: Call getLifetimeVariable for deeper analysis
+    if (!var)
+        return tok;
+    if (var->isLocal() || var->isArgument())
+        return tok;
+    const Token* parent = getParentMember(tok);
+    if (parent != tok)
+        return getParentLifetime(parent);
+    return tok;
+}
+
 bool astIsLHS(const Token* tok)
 {
     if (!tok)
@@ -448,8 +464,6 @@ bool isAliasOf(const Token *tok, nonneg int varid)
 {
     if (tok->varId() == varid)
         return false;
-    if (tok->varId() == 0)
-        return false;
     for (const ValueFlow::Value &val : tok->values()) {
         if (!val.isLocalLifetimeValue())
             continue;

lib/astutils.h

@@ -97,6 +97,8 @@ const Token* astParentSkipParens(const Token* tok);
 
 const Token* getParentMember(const Token * tok);
 
+const Token* getParentLifetime(const Token* tok);
+
 bool astIsLHS(const Token* tok);
 bool astIsRHS(const Token* tok);
 

lib/checkautovariables.cpp

@@ -432,22 +432,6 @@ static bool isDeadScope(const Token * tok, const Scope * scope)
     return false;
 }
 
-static const Token * getParentLifetime(const Token *tok)
-{
-    if (!tok)
-        return tok;
-    const Variable * var = tok->variable();
-    // TODO: Call getLifetimeVariable for deeper analysis
-    if (!var)
-        return tok;
-    if (var->isLocal())
-        return tok;
-    const Token * parent = getParentMember(tok);
-    if (parent != tok)
-        return getParentLifetime(parent);
-    return tok;
-}
-
 static int getPointerDepth(const Token *tok)
 {
     if (!tok)

lib/checkother.cpp

@@ -31,6 +31,7 @@
 #include "token.h"
 #include "tokenize.h"
 #include "utils.h"
+#include "valueflow.h"
 
 #include <algorithm> // find_if()
 #include <list>
@@ -1363,9 +1364,20 @@ void CheckOther::checkConstVariable()
             continue;
         if (isVariableChanged(var, mSettings, mTokenizer->isCPP()))
             continue;
-        if (Function::returnsReference(function) &&
+        if (Function::returnsReference(function)) {
-            Token::findmatch(var->nameToken(), "return %varid% ;|[|.", scope->bodyEnd, var->declarationId()))
+            std::vector<const Token*> returns = Function::findReturns(function);
+            if (std::any_of(returns.begin(), returns.end(), [&](const Token* retTok) {
+                    if (retTok->varId() == var->declarationId())
+                        return true;
+                    while (Token::simpleMatch(retTok, "."))
+                        retTok = retTok->astOperand2();
+                    const Variable* retVar = getLifetimeVariable(getParentLifetime(retTok));
+                    if (!retVar)
+                        return false;
+                    return retVar->declarationId() == var->declarationId();
+                }))
                 continue;
+        }
         // Skip if address is taken
         if (Token::findmatch(var->nameToken(), "& %varid%", scope->bodyEnd, var->declarationId()))
             continue;

lib/symboldatabase.cpp

@@ -2439,6 +2439,32 @@ bool Function::returnsReference(const Function* function, bool unknown)
     return false;
 }
 
+std::vector<const Token*> Function::findReturns(const Function* f)
+{
+    std::vector<const Token*> result;
+    if (!f)
+        return result;
+    const Scope* scope = f->functionScope;
+    if (!scope)
+        return result;
+    for (const Token* tok = scope->bodyStart->next(); tok && tok != scope->bodyEnd; tok = tok->next()) {
+        if (tok->str() == "{" && tok->scope() &&
+            (tok->scope()->type == Scope::eLambda || tok->scope()->type == Scope::eClass)) {
+            tok = tok->link();
+            continue;
+        }
+        if (Token::simpleMatch(tok->astParent(), "return")) {
+            result.push_back(tok);
+        }
+        // Skip lambda functions since the scope may not be set correctly
+        const Token* lambdaEndToken = findLambdaEndToken(tok);
+        if (lambdaEndToken) {
+            tok = lambdaEndToken;
+        }
+    }
+    return result;
+}
+
 const Token * Function::constructorMemberInitialization() const
 {
     if (!isConstructor() || !functionScope || !functionScope->bodyStart)

lib/symboldatabase.h

@@ -896,6 +896,8 @@ public:
 
     static bool returnsReference(const Function* function, bool unknown = false);
 
+    static std::vector<const Token*> findReturns(const Function* f);
+
     const Token* returnDefEnd() const {
         if (this->hasTrailingReturnType()) {
             return Token::findmatch(retDef, "{|;");

lib/valueflow.cpp

@@ -2718,30 +2718,6 @@ static void valueFlowForward(Token* startToken,
     }
 }
 
-static std::vector<const Token*> findReturns(const Function* f)
-{
-    std::vector<const Token*> result;
-    const Scope* scope = f->functionScope;
-    if (!scope)
-        return result;
-    for (const Token* tok = scope->bodyStart->next(); tok && tok != scope->bodyEnd; tok = tok->next()) {
-        if (tok->str() == "{" && tok->scope() &&
-            (tok->scope()->type == Scope::eLambda || tok->scope()->type == Scope::eClass)) {
-            tok = tok->link();
-            continue;
-        }
-        if (Token::simpleMatch(tok->astParent(), "return")) {
-            result.push_back(tok);
-        }
-        // Skip lambda functions since the scope may not be set correctly
-        const Token* lambdaEndToken = findLambdaEndToken(tok);
-        if (lambdaEndToken) {
-            tok = lambdaEndToken;
-        }
-    }
-    return result;
-}
-
 static int getArgumentPos(const Variable *var, const Function *f)
 {
     auto arg_it = std::find_if(f->argumentList.begin(), f->argumentList.end(), [&](const Variable &v) {
@@ -2850,6 +2826,16 @@ std::vector<LifetimeToken> getLifetimeTokens(const Token* tok, ValueFlow::Value:
                     return {{tok, true, std::move(errorPath)}};
                 if (vartok)
                     return getLifetimeTokens(vartok, std::move(errorPath), depth - 1);
+            } else if (Token::simpleMatch(var->nameToken()->astParent(), ":") &&
+                       var->nameToken()->astParent()->astParent() &&
+                       Token::simpleMatch(var->nameToken()->astParent()->astParent()->previous(), "for (")) {
+                errorPath.emplace_back(var->nameToken(), "Assigned to reference.");
+                const Token* vartok = var->nameToken();
+                if (vartok == tok)
+                    return {{tok, true, std::move(errorPath)}};
+                const Token* contok = var->nameToken()->astParent()->astOperand2();
+                if (contok)
+                    return getLifetimeTokens(contok, std::move(errorPath), depth - 1);
             } else {
                 return std::vector<LifetimeToken> {};
             }
@@ -2860,7 +2846,7 @@ std::vector<LifetimeToken> getLifetimeTokens(const Token* tok, ValueFlow::Value:
             if (!Function::returnsReference(f))
                 return {{tok, std::move(errorPath)}};
             std::vector<LifetimeToken> result;
-            std::vector<const Token*> returns = findReturns(f);
+            std::vector<const Token*> returns = Function::findReturns(f);
             for (const Token* returnTok : returns) {
                 if (returnTok == tok)
                     continue;
@@ -2947,6 +2933,12 @@ const Variable* getLifetimeVariable(const Token* tok, ValueFlow::Value::ErrorPat
     return nullptr;
 }
 
+const Variable* getLifetimeVariable(const Token* tok)
+{
+    ValueFlow::Value::ErrorPath errorPath;
+    return getLifetimeVariable(tok, errorPath, nullptr);
+}
+
 static bool isNotLifetimeValue(const ValueFlow::Value& val)
 {
     return !val.isLifetimeValue();
@@ -3394,7 +3386,7 @@ static void valueFlowLifetimeFunction(Token *tok, TokenList *tokenlist, ErrorLog
         const Function *f = tok->function();
         if (Function::returnsReference(f))
             return;
-        std::vector<const Token*> returns = findReturns(f);
+        std::vector<const Token*> returns = Function::findReturns(f);
         const bool inconclusive = returns.size() > 1;
         for (const Token* returnTok : returns) {
             if (returnTok == tok)

lib/valueflow.h

@@ -359,6 +359,8 @@ std::vector<LifetimeToken> getLifetimeTokens(const Token* tok, ValueFlow::Value:
 
 const Variable* getLifetimeVariable(const Token* tok, ValueFlow::Value::ErrorPath& errorPath, bool* addressOf = nullptr);
 
+const Variable* getLifetimeVariable(const Token* tok);
+
 bool isLifetimeBorrowed(const Token *tok, const Settings *settings);
 
 std::string lifetimeType(const Token *tok, const ValueFlow::Value *val);

test/testother.cpp

@@ -1959,6 +1959,24 @@ private:
               "}\n");
         ASSERT_EQUALS("", errout.str());
 
+        check("int* f(std::list<int>& x, unsigned int y) {\n"
+              "    for (int& m : x) {\n"
+              "        if (m == y)\n"
+              "            return &m;\n"
+              "    }\n"
+              "    return nullptr;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("int& f(std::list<int>& x, int& y) {\n"
+              "    for (int& m : x) {\n"
+              "        if (m == y)\n"
+              "            return m;\n"
+              "    }\n"
+              "    return y;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         check("void e();\n"
               "void g(void);\n"
               "void h(void);\n"