Improved fix for #8978 (False positive: Variable assigned value that is never used when assigning via iterator)

cfg/cppcheck-cfg.rng

@@ -447,6 +447,23 @@
         <attribute name="class-name"><ref name="DATA-EXTNAME"/></attribute>
       </element>
 
+      <element name="type-checks">
+        <optional>
+          <element name="unusedvar">
+            <zeroOrMore>
+              <choice>
+                <element name="check">
+                  <ref name="DATA-EXTNAME"/>
+                </element>
+                <element name="suppress">
+                  <ref name="DATA-EXTNAME"/>
+                </element>
+              <choice>
+            </zeroOrMore>
+          </element>
+        </optional>
+      </element>
+
       <element name="podtype">
         <attribute name="name"><ref name="DATA-EXTNAME"/></attribute>
         <optional>

cfg/std.cfg

@@ -7993,6 +7993,12 @@ initializer list (7) string& replace (const_iterator i1, const_iterator i2, init
   <smart-pointer class-name="std::shared_ptr"/>
   <smart-pointer class-name="std::unique_ptr"/>
   <smart-pointer class-name="std::weak_ptr"/>
+  <type-checks>
+    <unusedvar>
+      <suppress>std::insert_iterator</suppress>
+      <check>std::pair</check>
+    </unusedvar>
+  </type-checks>
   <podtype name="char8_t,std::char8_t" sign="u" size="1"/>
   <podtype name="char16_t,std::char16_t" sign="u" size="2"/>
   <podtype name="char32_t,std::char32_t" sign="u" size="4"/>

lib/checkunusedvar.cpp

@@ -1185,6 +1185,7 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 op1tok = op1tok->astOperand1();
 
             const Variable *op1Var = op1tok ? op1tok->variable() : nullptr;
+            std::string bailoutTypeName;
             if (op1Var) {
                 if (op1Var->isReference() && op1Var->nameToken() != tok->astOperand1())
                     // todo: check references
@@ -1200,9 +1201,21 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 // Bailout for unknown template classes, we have no idea what side effects such assignments have
                 if (mTokenizer->isCPP() &&
                     op1Var->isClass() &&
-                    (!op1Var->valueType() || op1Var->valueType()->type == ValueType::Type::UNKNOWN_TYPE) &&
+                    (!op1Var->valueType() || op1Var->valueType()->type == ValueType::Type::UNKNOWN_TYPE)) {
-                    Token::findsimplematch(op1Var->typeStartToken(), "<", op1Var->typeEndToken()))
+                    // Check in the library if we should bailout or not..
+                    const std::string typeName = op1Var->getTypeName();
+                    switch (mSettings->library.getTypeCheck("unusedvar", typeName)) {
+                    case Library::TypeCheck::def:
+                        if (!mSettings->checkLibrary)
                             continue;
+                        bailoutTypeName = typeName;
+                        break;
+                    case Library::TypeCheck::check:
+                        break;
+                    case Library::TypeCheck::suppress:
+                        continue;
+                    };
+                }
             }
 
             // Is there a redundant assignment?
@@ -1211,10 +1224,21 @@ void CheckUnusedVar::checkFunctionVariableUsage()
             const Token *expr = varDecl ? varDecl : tok->astOperand1();
 
             FwdAnalysis fwdAnalysis(mTokenizer->isCPP(), mSettings->library);
-            if (fwdAnalysis.unusedValue(expr, start, scope->bodyEnd))
+            if (fwdAnalysis.unusedValue(expr, start, scope->bodyEnd)) {
+                if (!bailoutTypeName.empty()) {
+                    if (mSettings->checkLibrary && mSettings->isEnabled(Settings::INFORMATION)) {
+                        reportError(tok,
+                                    Severity::information,
+                                    "checkLibraryCheckType",
+                                    "--check-library: Provide <type-checks><unusedvar> configuration for " + bailoutTypeName);
+                    }
+                    continue;
+                }
+
                 // warn
                 unreadVariableError(tok, expr->expressionString(), false);
             }
+        }
 
         // varId, usage {read, write, modified}
         Variables variables;

lib/library.cpp

@@ -511,6 +511,22 @@ Library::Error Library::load(const tinyxml2::XMLDocument &doc)
                 smartPointers.insert(className);
         }
 
+        else if (nodename == "type-checks") {
+            for (const tinyxml2::XMLElement *checkNode = node->FirstChildElement(); checkNode; checkNode = checkNode->NextSiblingElement()) {
+                const std::string &checkName = checkNode->Name();
+                for (const tinyxml2::XMLElement *checkTypeNode = checkNode->FirstChildElement(); checkTypeNode; checkTypeNode = checkTypeNode->NextSiblingElement()) {
+                    const std::string checkTypeName = checkTypeNode->Name();
+                    const char *typeName = checkTypeNode->GetText();
+                    if (!typeName)
+                        continue;
+                    if (checkTypeName == "check")
+                        mTypeChecks[std::pair<std::string,std::string>(checkName, typeName)] = TypeCheck::check;
+                    else if (checkTypeName == "suppress")
+                        mTypeChecks[std::pair<std::string,std::string>(checkName, typeName)] = TypeCheck::suppress;
+                }
+            }
+        }
+
         else if (nodename == "podtype") {
             const char * const name = node->Attribute("name");
             if (!name)
@@ -1405,3 +1421,8 @@ CPPCHECKLIB const Library::Container * getLibraryContainer(const Token * tok)
     return tok->valueType()->container;
 }
 
+Library::TypeCheck Library::getTypeCheck(const std::string &check, const std::string &typeName) const
+{
+    auto it = mTypeChecks.find(std::pair<std::string, std::string>(check, typeName));
+    return it == mTypeChecks.end() ? TypeCheck::def : it->second;
+}

lib/library.h

@@ -478,6 +478,10 @@ public:
 
     static bool isContainerYield(const Token * const cond, Library::Container::Yield y, const std::string& fallback="");
 
+    /** Suppress/check a type */
+    enum class TypeCheck { def, check, suppress };
+    TypeCheck getTypeCheck(const std::string &check, const std::string &typeName) const;
+
 private:
     // load a <function> xml node
     Error loadFunction(const tinyxml2::XMLElement * const node, const std::string &name, std::set<std::string> &unknown_elements);
@@ -557,6 +561,7 @@ private:
     std::map<std::string, struct PodType> mPodTypes; // pod types
     std::map<std::string, PlatformType> mPlatformTypes; // platform independent typedefs
     std::map<std::string, Platform> mPlatforms; // platform dependent typedefs
+    std::map<std::pair<std::string,std::string>, TypeCheck> mTypeChecks;
 
     const ArgumentChecks * getarg(const Token *ftok, int argnr) const;
 

lib/symboldatabase.cpp

@@ -1857,6 +1857,15 @@ const Type *Variable::smartPointerType() const
     return nullptr;
 }
 
+std::string Variable::getTypeName() const
+{
+    std::string ret;
+    // TODO: For known types, generate the full type name
+    for (const Token *typeTok = mTypeStartToken; Token::Match(typeTok, "%name%|::") && typeTok->varId() == 0; typeTok = typeTok->next())
+        ret += typeTok->str();
+    return ret;
+}
+
 Function::Function(const Tokenizer *mTokenizer,
                    const Token *tok,
                    const Scope *scope,

lib/symboldatabase.h

@@ -616,6 +616,8 @@ public:
         return mAccess;
     }
 
+    std::string getTypeName() const;
+
 private:
     // only symbol database can change the type
     friend class SymbolDatabase;

man/reference-cfg-format.md

@@ -487,6 +487,24 @@ The first argument that the function takes is a pointer. It must not be a null p
 
 The second argument the function takes is a pointer. It must not be null. And it must point at initialized data. Using `<not-null>` and `<not-uninit>` is correct. Moreover it must point at a zero-terminated string so `<strz>` is also used.
 
+# `<type-checks>`; check or suppress
+
+The `<type-checks>`configuration tells Cppcheck to show or suppress warnings for a certain type.
+
+Example:
+
+    <?xml version="1.0"?>
+    <def>
+      <type-checks>
+        <unusedvar>
+          <check>foo</check>
+          <suppress>bar</suppress>
+        </unusedvar>
+      </type-checks>
+    </def>
+
+In the `unusedvar` checking the `foo` type will be checked. Warnings for `bar` type variables will be suppressed.
+
 # `<define>`
 
 Libraries can be used to define preprocessor macros as well. For example:

test/testunusedvar.cpp

@@ -33,6 +33,8 @@ private:
 
     void run() OVERRIDE {
         settings.addEnabled("style");
+        settings.addEnabled("information");
+        settings.checkLibrary = true;
         LOAD_LIB_2(settings.library, "std.cfg");
 
         TEST_CASE(emptyclass);  // #5355 - False positive: Variable is not assigned a value.
@@ -3535,13 +3537,18 @@ private:
                               "}");
         ASSERT_EQUALS("", errout.str());
 
-        // FIXME : this is probably inconclusive
+        functionVariableUsage("void f() {\n"  // unknown class => library configuration is needed
-        functionVariableUsage("void f() {\n"
                               "  Fred fred;\n"
                               "  int *a; a = b;\n"
                               "  fred += a;\n"
                               "}");
-        ASSERT_EQUALS("[test.cpp:4]: (style) Variable 'fred' is assigned a value that is never used.\n", errout.str());
+        ASSERT_EQUALS("[test.cpp:4]: (information) --check-library: Provide <type-checks><unusedvar> configuration for Fred\n", errout.str());
+
+        functionVariableUsage("void f() {\n"
+                              "  std::pair<int,int> fred;\n"  // class with library configuration
+                              "  fred = x;\n"
+                              "}");
+        ASSERT_EQUALS("[test.cpp:3]: (style) Variable 'fred' is assigned a value that is never used.\n", errout.str());
     }
 
     void localvarFor() {