fix #13269: FN: unusedVariable with structured binding (#7701)

Author: ludviggunne

lib/checkunusedvar.cpp

@@ -1186,7 +1186,24 @@ void CheckUnusedVar::checkFunctionVariableUsage()
         const Token* lambdaOrInlineStart{};
         const bool hasLambdaOrInline = scope->hasInlineOrLambdaFunction(&lambdaOrInlineStart);
 
+        const Token *nextStructuredBindingTok = nullptr;
+        std::vector<std::pair<const Token*, const Token*>> unusedStructuredBindingTokens;
+        size_t structuredBindingTokCount = 0;
+
         for (const Token *tok = scope->bodyStart; tok != scope->bodyEnd; tok = tok->next()) {
+            if (nextStructuredBindingTok) {
+                tok = nextStructuredBindingTok;
+            } else {
+                if (structuredBindingTokCount > 0 && structuredBindingTokCount == unusedStructuredBindingTokens.size()) {
+                    for (const auto &pair : unusedStructuredBindingTokens) {
+                        unreadVariableError(pair.first, pair.second->expressionString(), false);
+                    }
+                }
+                structuredBindingTokCount = 0;
+                unusedStructuredBindingTokens.clear();
+            }
+            nextStructuredBindingTok = nullptr;
+
             if (findLambdaEndToken(tok))
                 // todo: handle lambdas
                 break;
@@ -1196,6 +1213,16 @@ void CheckUnusedVar::checkFunctionVariableUsage()
             const Token *varDecl = nullptr;
             if (tok->variable() && tok->variable()->nameToken() == tok) {
                 const Token * eq = tok->next();
+                if (isStructuredBindingVariable(tok->variable())) {
+                    structuredBindingTokCount++;
+                    while (!Token::simpleMatch(eq, "]")) {
+                        eq = eq->next();
+                        if (eq->variable() && !nextStructuredBindingTok)
+                            nextStructuredBindingTok = eq;
+                    }
+                    if (eq)
+                        eq = eq->next();
+                }
                 while (Token::simpleMatch(eq, "["))
                     eq = eq->link()->next();
                 if (Token::simpleMatch(eq, ") (") && Token::simpleMatch(eq->linkAt(1), ") ="))
@@ -1333,8 +1360,12 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                     continue;
 
                 // warn
-                if (!expr->variable() || !expr->variable()->isMaybeUnused())
-                    unreadVariableError(tok, expr->expressionString(), false);
+                if (!expr->variable() || !expr->variable()->isMaybeUnused()) {
+                    if (structuredBindingTokCount > 0)
+                        unusedStructuredBindingTokens.emplace_back(tok, expr);
+                    else
+                        unreadVariableError(tok, expr->expressionString(), false);
+                }
             }
         }
 

test/testunusedvar.cpp

@@ -259,6 +259,8 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(escapeAlias); // #9150
         TEST_CASE(volatileData); // #9280
         TEST_CASE(globalData);
+
+        TEST_CASE(structuredBinding); // #13269
     }
 
     struct FunctionVariableUsageOptions
@@ -7197,6 +7199,42 @@ class TestUnusedVar : public TestFixture {
             "}");
         ASSERT_EQUALS("", errout_str());
     }
+
+    void structuredBinding() { // #13269
+        functionVariableUsage("int main()\n"
+                              "{\n"
+                              "    auto [a, b] = std::make_pair(42, 0.42);\n"
+                              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:17]: (style) Variable 'a' is assigned a value that is never used. [unreadVariable]\n"
+                      "[test.cpp:3:17]: (style) Variable 'b' is assigned a value that is never used. [unreadVariable]\n", errout_str());
+
+        functionVariableUsage("int main()\n"
+                              "{\n"
+                              "    auto [a, b] = std::make_pair(42, 0.42);\n"
+                              "    (void) a;\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        functionVariableUsage("int main()\n"
+                              "{\n"
+                              "    auto [a, b] = std::make_pair(42, 0.42);\n"
+                              "    (void) b;\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        functionVariableUsage("int main()\n"
+                              "{\n"
+                              "    auto [a, b, c] = std::make_pair(42, 0.42);\n"
+                              "    (void) b;\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        functionVariableUsage("int main()\n"
+                              "{\n"
+                              "    [[maybe_unused]] auto [a2, b3] = std::make_pair(42, 0.42);\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
+    }
 };
 
 REGISTER_TEST(TestUnusedVar)