Maybeunusedsupport (#2570)

* Add rudimentary support for [[maybe_unused]]

* Add more test cases. use the symboldatabase rather than reparsing. Fix travis error.

* test review actions

* change var to usage._var

lib/checkunusedvar.cpp

@@ -1246,6 +1246,7 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 }
 
                 // warn
+                if(!expr->variable() || !expr->variable()->isMaybeUnused())
                     unreadVariableError(tok, expr->expressionString(), false);
             }
         }
@@ -1281,9 +1282,11 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                 allocatedButUnusedVariableError(usage._lastAccess, varname);
 
             // variable has not been written, read, or modified
-            else if (usage.unused() && !usage._modified)
+            else if (usage.unused() && !usage._modified) {
+                if (!usage._var->isMaybeUnused()) {
                     unusedVariableError(usage._var->nameToken(), varname);
-
+                }
+            }
             // variable has not been written but has been modified
             else if (usage._modified && !usage._write && !usage._allocateMemory && var && !var->isStlType())
                 unassignedVariableError(usage._var->nameToken(), varname);

lib/symboldatabase.cpp

@@ -1889,6 +1889,10 @@ void Variable::evaluate(const Settings* settings)
             setFlag(fIsReference, true); // Set also fIsReference
         }
 
+        if (tok->isMaybeUnused()) {
+            setFlag(fIsMaybeUnused, true);
+        }
+
         if (tok->str() == "<" && tok->link())
             tok = tok->link();
         else

lib/symboldatabase.h

@@ -193,7 +193,8 @@ class CPPCHECKLIB Variable {
         fIsStlString  = (1 << 11),  /** @brief std::string|wstring|basic_string&lt;T&gt;|u16string|u32string */
         fIsFloatType  = (1 << 12),  /** @brief Floating point type */
         fIsVolatile   = (1 << 13),  /** @brief volatile */
-        fIsSmartPointer = (1 << 14)   /** @brief std::shared_ptr|unique_ptr */
+        fIsSmartPointer = (1 << 14),/** @brief std::shared_ptr|unique_ptr */
+        fIsMaybeUnused = (1 << 15), /** @brief marked [[maybe_unused]] */
     };
 
     /**
@@ -618,6 +619,10 @@ public:
         return type() && type()->isEnumType();
     }
 
+    bool isMaybeUnused() const {
+        return getFlag(fIsMaybeUnused);
+    }
+
     const ValueType *valueType() const {
         return mValueType;
     }

lib/token.h

@@ -541,6 +541,12 @@ public:
     void isAttributeNodiscard(const bool value) {
         setFlag(fIsAttributeNodiscard, value);
     }
+    bool isMaybeUnused() const {
+        return getFlag(fIsMaybeUnused);
+    }
+    void isMaybeUnused(const bool value) {
+        setFlag(fIsMaybeUnused, value);
+    }
     void setCppcheckAttribute(TokenImpl::CppcheckAttributes::Type type, MathLib::bigint value) {
         mImpl->setCppcheckAttribute(type, value);
     }
@@ -1155,6 +1161,7 @@ private:
         fIncompleteVar          = (1 << 25),
         fConstexpr              = (1 << 26),
         fExternC                = (1 << 27),
+        fIsMaybeUnused          = (1 << 28), // [[maybe_unsed]]
     };
 
     Token::Type mTokType;

lib/tokenize.cpp

@@ -10246,6 +10246,11 @@ void Tokenizer::simplifyCPPAttribute()
                 else
                     head->previous()->isAttributeNodiscard(true);
             }
+        } else if (Token::simpleMatch(tok->tokAt(2), "maybe_unused")) {
+            Token* head = tok->tokAt(5);
+            while (isCPPAttribute(head))
+                head = head->tokAt(5);
+            head->isMaybeUnused(true);
         } else if (Token::Match(tok->previous(), ") [ [ expects|ensures|assert default|audit|axiom| : %name% <|<=|>|>= %num% ] ]")) {
             const Token *vartok = tok->tokAt(4);
             if (vartok->str() == ":")

test/testunusedvar.cpp

@@ -148,6 +148,7 @@ private:
         TEST_CASE(localvarconst1);
         TEST_CASE(localvarconst2);
         TEST_CASE(localvarreturn); // ticket #9167
+        TEST_CASE(localvarmaybeunused);
 
         TEST_CASE(localvarthrow); // ticket #3687
 
@@ -4160,6 +4161,87 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void localvarmaybeunused() {
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] int x;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("[[nodiscard]] int getX() { return 4; }\n"
+                              "int main() {\n"
+                              "    [[maybe_unused]] int x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("[[nodiscard]] int getX() { return 4; }\n"
+                              "int main() {\n"
+                              "    [[maybe_unused]] int x = getX();\n"
+                              "    x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("[[nodiscard]] int getX() { return 4; }\n"
+                              "int main() {\n"
+                              "    [[maybe_unused]] int x = getX();\n"
+                              "    x = getX();\n"
+                              "    std::cout << x;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] const int x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] const int& x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] const int* x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] int& x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] int* x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] auto x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] auto&& x = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] int x[] = getX();\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] constexpr volatile static int x = 1;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("[[maybe_unused]] inline int x = 1;");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("int main() {\n"
+                              "    [[maybe_unused]] [[anotherattribute]] const int* = 1;\n"
+                              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void localvarthrow() { // ticket #3687
         functionVariableUsage("void foo() {\n"
                               "    try {}"