Fix #14075 (False positive: unusedStructMember, member usage by alignas is ignored)

Author: danmar

lib/checkunusedvar.cpp

@@ -1628,6 +1628,15 @@ void CheckUnusedVar::checkStructMemberUsage()
                         break;
                     }
                 }
+                // Member referenced in alignas
+                if (tok->hasAttributeAlignas()) {
+                    for (const std::string& alignasExpr : tok->getAttributeAlignas()) {
+                        if (alignasExpr == var.name()) {
+                            use = true;
+                            break;
+                        }
+                    }
+                }
                 if (tok->variable() != &var)
                     continue;
                 if (tok != var.nameToken()) {

test/testunusedvar.cpp

@@ -71,6 +71,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(structmember26); // #13345
         TEST_CASE(structmember27); // #13367
         TEST_CASE(structmember28);
+        TEST_CASE(structmember29); // #14075
         TEST_CASE(structmember_macro);
         TEST_CASE(structmember_template_argument); // #13887 - do not report that member used in template argument is unused
         TEST_CASE(classmember);
@@ -2010,6 +2011,15 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:2:18]: (style) struct member 'S::a' is never used. [unusedStructMember]\n", errout_str());
     }
 
+    void structmember29() { // #14075 - alignas false positive
+        checkStructMemberUsage("struct S {\n"
+                               "    static constexpr size_t cDataAlign = 8;\n"
+                               "    static constexpr size_t cDataSize = 128;\n"
+                               "    alignas(cDataAlign) std::array<uint8_t, cDataSize> storage{};\n"
+                               "};\n");
+        ASSERT_EQUALS("[test.cpp:4:56]: (style) struct member 'S::storage' is never used. [unusedStructMember]\n", errout_str());
+    }
+
     void structmember_macro() {
         checkStructMemberUsageP("#define S(n) struct n { int a, b, c; };\n"
                                 "S(unused);\n");