Fix #13887 (False positive: template argument reported as unused struct member)

lib/checkunusedvar.cpp

@@ -1575,6 +1575,9 @@ void CheckUnusedVar::checkStructMemberUsage()
             if (isInherited && !var.isPrivate())
                 continue;
 
+            if (mTokenizer->isVarUsedInTemplate(var.declarationId()))
+                continue;
+
             // Check if the struct member variable is used anywhere in the file
             bool use = false;
             for (const Token *tok = mTokenizer->tokens(); tok; tok = tok->next()) {

lib/templatesimplifier.cpp

@@ -1647,6 +1647,12 @@ void TemplateSimplifier::expandTemplate(
 
     std::vector<newInstantiation> newInstantiations;
 
+    for (const Token* tok = templateInstantiation.token()->next()->findClosingBracket();
+         tok && tok != templateInstantiation.token(); tok = tok->previous()) {
+        if (tok->isName())
+            mUsedVariables[newName].insert(tok->str());
+    }
+
     // add forward declarations
     if (copy && isClass) {
         templateDeclaration.token()->insertTokenBefore(templateDeclarationToken->strAt(1));

lib/templatesimplifier.h

@@ -54,6 +54,10 @@ class CPPCHECKLIB TemplateSimplifier {
         return mDump;
     }
 
+    const std::map<std::string, std::set<std::string>>& getUsedVariables() const {
+        return mUsedVariables;
+    }
+
     /**
      */
     void checkComplicatedSyntaxErrorsInTemplates();
@@ -510,6 +514,8 @@ class CPPCHECKLIB TemplateSimplifier {
     std::vector<TokenAndName> mTypesUsedInTemplateInstantiation;
     std::unordered_map<const Token*, int> mTemplateNamePos;
     std::string mDump;
+
+    std::map<std::string, std::set<std::string>> mUsedVariables;
 };
 
 /// @}

lib/tokenize.cpp

@@ -4406,10 +4406,26 @@ static void setVarIdStructMembers(Token *&tok1,
     tok1 = tok;
 }
 
+static void addTemplateVarIdUsage(const std::string &tokstr,
+                                  const std::map<std::string, std::set<std::string>>& templateVarUsage,
+                                  const std::unordered_map<std::string, nonneg int>& variableMap,
+                                  std::set<nonneg int>& templateVarIdUsage) {
+    const auto v = templateVarUsage.find(tokstr);
+    if (v != templateVarUsage.end()) {
+        for (const std::string& varname: v->second) {
+            const auto it = variableMap.find(varname);
+            if (it != variableMap.end())
+                templateVarIdUsage.insert(it->second);
+        }
+    }
+}
+
 static bool setVarIdClassDeclaration(Token* const startToken,
                                      VariableMap& variableMap,
                                      const nonneg int scopeStartVarId,
-                                     std::map<nonneg int, std::map<std::string, nonneg int>>& structMembers)
+                                     const std::map<std::string, std::set<std::string>>& templateVarUsage,
+                                     std::map<nonneg int, std::map<std::string, nonneg int>>& structMembers,
+                                     std::set<nonneg int>& templateVarIdUsage)
 {
     // end of scope
     const Token* const endToken = startToken->link();
@@ -4476,6 +4492,8 @@ static bool setVarIdClassDeclaration(Token* const startToken,
                     if (it != variableMap.map(false).end()) {
                         tok->varId(it->second);
                         setVarIdStructMembers(tok, structMembers, variableMap.getVarId());
+                    } else if (tok->str().back() == '>') {
+                        addTemplateVarIdUsage(tok->str(), templateVarUsage, variableMap.map(false), templateVarIdUsage);
                     }
                 }
             }
@@ -4655,7 +4673,9 @@ void Tokenizer::setVarIdPass1()
                         if (!setVarIdClassDeclaration(tok->link(),
                                                       variableMap,
                                                       scopeStack.top().startVarid,
-                                                      structMembers)) {
+                                                      mTemplateSimplifier->getUsedVariables(),
+                                                      structMembers,
+                                                      mTemplateVarIdUsage)) {
                             syntaxError(nullptr);
                         }
                     }
@@ -4742,6 +4762,16 @@ void Tokenizer::setVarIdPass1()
 
             if (decl) {
                 if (cpp) {
+                    for (const Token* tok3 = tok->next(); tok3->isName(); tok3 = tok3->next()) {
+                        addTemplateVarIdUsage(tok3->str(),
+                                              mTemplateSimplifier->getUsedVariables(),
+                                              variableMap.map(false),
+                                              mTemplateVarIdUsage);
+                        addTemplateVarIdUsage(tok3->str(),
+                                              mTemplateSimplifier->getUsedVariables(),
+                                              variableMap.map(true),
+                                              mTemplateVarIdUsage);
+                    }
                     if (Token *declTypeTok = Token::findsimplematch(tok, "decltype (", tok2)) {
                         for (Token *declTok = declTypeTok->linkAt(1); declTok != declTypeTok; declTok = declTok->previous()) {
                             if (declTok->isName() && !Token::Match(declTok->previous(), "::|.") && variableMap.hasVariable(declTok->str()))
@@ -4855,6 +4885,13 @@ void Tokenizer::setVarIdPass1()
                     continue;
             }
 
+            if (tok->str().back() == '>') {
+                addTemplateVarIdUsage(tok->str(),
+                                      mTemplateSimplifier->getUsedVariables(),
+                                      variableMap.map(globalNamespace),
+                                      mTemplateVarIdUsage);
+            }
+
             // function declaration inside executable scope? Function declaration is of form: type name "(" args ")"
             if (scopeStack.top().isExecutable && !scopeStack.top().isStructInit && Token::Match(tok, "%name% [,)[]")) {
                 bool par = false;
@@ -6171,6 +6208,12 @@ void Tokenizer::dump(std::ostream &out) const
     outs += dumpTypedefInfo();
 
     outs += mTemplateSimplifier->dump();
+    if (!mTemplateVarIdUsage.empty()) {
+        outs += "  <template-varid-usage>\n";
+        for (nonneg int id: mTemplateVarIdUsage)
+            outs += "    <var id=\"" + std::to_string(id) + "\"/>\n";
+        outs += "  </template-varid-usage>\n";
+    }
 
     out << outs;
 }

lib/tokenize.h

@@ -28,6 +28,7 @@
 #include <iosfwd>
 #include <list>
 #include <map>
+#include <set>
 #include <string>
 #include <vector>
 
@@ -81,6 +82,10 @@ class CPPCHECKLIB Tokenizer {
 
     bool simplifyTokens1(const std::string &configuration, int fileIndex=0);
 
+    bool isVarUsedInTemplate(nonneg int id) const {
+        return mTemplateVarIdUsage.count(id) != 0;
+    }
+
 private:
     /** Set variable id */
     void setVarId();
@@ -641,6 +646,8 @@ class CPPCHECKLIB Tokenizer {
 
     TemplateSimplifier * const mTemplateSimplifier;
 
+    std::set<nonneg int> mTemplateVarIdUsage;
+
     /** E.g. "A" for code where "#ifdef A" is true. This is used to
         print additional information in error situations. */
     std::string mConfiguration;

test/testunusedvar.cpp

@@ -71,6 +71,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(structmember26); // #13345
         TEST_CASE(structmember27); // #13367
         TEST_CASE(structmember_macro);
+        TEST_CASE(structmember_template_argument); // #13887 - do not report that member used in template argument is unused
         TEST_CASE(classmember);
         TEST_CASE(structmemberStructuredBinding); // #13107
 
@@ -2003,6 +2004,15 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("", errout_str());
     }
 
+    void structmember_template_argument() { // #13887 - False positive
+        checkStructMemberUsage("template <class T, int i> struct A{ T buf[i]; }\n"
+                               "struct B {\n"
+                               "    constexpr int x = 20;\n" // <- not unused
+                               "    A<uint32_t, x> a;\n" // <- unused
+                               "};");
+        ASSERT_EQUALS("[test.cpp:4:20]: (style) struct member 'B::a' is never used. [unusedStructMember]\n", errout_str());
+    }
+
     void classmember() {
         checkStructMemberUsage("class C {\n"
                                "    int i{};\n"