fix #14795: FP unusedStructMember when type is a template parameter (cppcheck-opensource#8600)

Author: ludviggunne

lib/checkunusedvar.cpp

@@ -1676,6 +1676,27 @@ void CheckUnusedVarImpl::checkStructMemberUsage()
                     if (use)
                         break;
                 }
+                // Class used in template with unknown definition
+                if (Token::Match(tok, "%name% <") && tok->linkAt(1)) {
+                    if (tok->function())
+                        continue;
+                    if (tok->type() && tok->type()->classScope)
+                        continue;
+                    const Token *start = tok;
+                    while (Token::Match(start->tokAt(-2), "%name% ::"))
+                        start = start->tokAt(-2);
+                    if (mSettings.library.detectContainer(start))
+                        continue;
+                    const Token *end = tok->linkAt(1);
+                    for (; tok != end; tok = tok->next()) {
+                        if (tok->type() && tok->type()->classScope == &scope) {
+                            use = true;
+                            break;
+                        }
+                    }
+                    if (use)
+                        break;
+                }
                 if (tok->variable() != &var)
                     continue;
                 if (tok != var.nameToken()) {

test/testunusedvar.cpp

@@ -80,6 +80,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(structmember32); // #14483
         TEST_CASE(structmember33);
         TEST_CASE(structmember34);
+        TEST_CASE(structmember35);
         TEST_CASE(structmember_macro);
         TEST_CASE(structmember_template_argument); // #13887 - do not report that member used in template argument is unused
         TEST_CASE(classmember);
@@ -2102,6 +2103,20 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:2:24]: (style) struct member 'S::p' is never used. [unusedStructMember]\n", errout_str());
     }
 
+    void structmember35() {
+        checkStructMemberUsage("struct S { int i; };\n"
+                               "int f() { return g<S>(); }\n");
+        ASSERT_EQUALS("", errout_str());
+
+        checkStructMemberUsage("struct S { int i; };\n"
+                               "int f() { A<S> *a = nullptr; (void) a; }\n");
+        ASSERT_EQUALS("", errout_str());
+
+        checkStructMemberUsage("struct S { int i; };\n"
+                               "int f() { const std::vector<S> a {}; (void) a; }\n");
+        ASSERT_EQUALS("[test.cpp:1:16]: (style) struct member 'S::i' is never used. [unusedStructMember]\n", errout_str());
+    }
+
     void structmember_macro() {
         checkStructMemberUsageP("#define S(n) struct n { int a, b, c; };\n"
                                 "S(unused);\n");