Fix FP with unreadVariable (#1859)

lib/astutils.cpp

@@ -1457,6 +1457,8 @@ const Token *FwdAnalysis::reassign(const Token *expr, const Token *startToken, c
 
 bool FwdAnalysis::unusedValue(const Token *expr, const Token *startToken, const Token *endToken)
 {
+    if (isEscapedAlias(expr))
+        return false;
     mWhat = What::UnusedValue;
     Result result = check(expr, startToken, endToken);
     return (result.type == FwdAnalysis::Result::Type::NONE || result.type == FwdAnalysis::Result::Type::RETURN) && !possiblyAliased(expr, startToken);
@@ -1516,6 +1518,25 @@ bool FwdAnalysis::possiblyAliased(const Token *expr, const Token *startToken) co
     return false;
 }
 
+bool FwdAnalysis::isEscapedAlias(const Token* expr)
+{
+    for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
+        for (const ValueFlow::Value &val : subexpr->values()) {
+            if (!val.isLocalLifetimeValue())
+                continue;
+            const Variable* var = val.tokvalue->variable();
+            if (!var)
+                continue;
+            if (!var->isLocal())
+                return true;
+            if (var->isArgument())
+                return true;
+            
+        }
+    }
+    return false;
+}
+
 bool FwdAnalysis::isNullOperand(const Token *expr)
 {
     if (!expr)

lib/astutils.h

@@ -206,6 +206,8 @@ public:
     /** Is there some possible alias for given expression */
     bool possiblyAliased(const Token *expr, const Token *startToken) const;
 
+    bool isEscapedAlias(const Token* expr);
+
     static bool isNullOperand(const Token *expr);
 private:
     /** Result of forward analysis */

lib/valueflow.cpp

@@ -3342,7 +3342,7 @@ static void valueFlowLifetime(TokenList *tokenlist, SymbolDatabase*, ErrorLogger
             valueFlowForwardLifetime(tok, tokenlist, errorLogger, settings);
         }
         // container lifetimes
-        else if (tok->variable() && Token::Match(tok, "%var% . begin|cbegin|rbegin|crbegin|end|cend|rend|crend|data|c_str (")) {
+        else if (tok->variable() && Token::Match(tok, "%var% . begin|cbegin|rbegin|crbegin|end|cend|rend|crend|data|c_str|find (")) {
             ErrorPath errorPath;
             const Library::Container * container = settings->library.detectContainer(tok->variable()->typeStartToken());
             if (!container)

test/testunusedvar.cpp

@@ -33,6 +33,7 @@ private:
 
     void run() OVERRIDE {
         settings.addEnabled("style");
+        LOAD_LIB_2(settings.library, "std.cfg");
 
         TEST_CASE(emptyclass);  // #5355 - False positive: Variable is not assigned a value.
         TEST_CASE(emptystruct);  // #5355 - False positive: Variable is not assigned a value.
@@ -197,6 +198,7 @@ private:
         TEST_CASE(bracesInitCpp11);// #7895 - "int var{123}" initialization
 
         TEST_CASE(argument);
+        TEST_CASE(escapeAlias); // #9150
     }
 
     void checkStructMemberUsage(const char code[]) {
@@ -4538,6 +4540,22 @@ private:
         );
         ASSERT_EQUALS("[test.cpp:2]: (style) Variable 'foo.x' is assigned a value that is never used.\n", errout.str());
     }
+
+    void escapeAlias() {
+        functionVariableUsage(
+            "struct A {\n"
+            "    std::map<int, int> m;\n"
+            "    void f(int key, int number) {\n"
+            "        auto pos = m.find(key);\n"
+            "        if (pos == m.end())\n"
+            "            m.insert(std::map<int, int>::value_type(key, number));\n"
+            "        else\n"
+            "            (*pos).second = number;\n"
+            "    }\n"
+            "};\n"
+        );
+        ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestUnusedVar)