Fix #15067: False positive: unreadVariable with overloaded subscript operator. (#8895)

Author: ludviggunne

lib/checkunusedvar.cpp

@@ -1288,6 +1288,11 @@ void CheckUnusedVarImpl::checkFunctionVariableUsage()
             while (Token::Match(op1tok, ".|[|*"))
                 op1tok = op1tok->astOperand1();
 
+            // Bail out for overloaded indexing
+            if (op1tok && op1tok->valueType() && op1tok->valueType()->pointer == 0 &&
+                op1tok->valueType()->type == ValueType::Type::RECORD && Token::simpleMatch(op1tok->astParent(), "["))
+                continue;
+
             // Assignment in macro => do not warn
             if (isAssignment && tok->isExpandedMacro() && op1tok && op1tok->isExpandedMacro())
                 continue;

test/testunusedvar.cpp

@@ -225,6 +225,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(localvarStruct13); // #10398
         TEST_CASE(localvarStruct14);
         TEST_CASE(localvarStructArray);
+        TEST_CASE(localvarOverloadedSubscript);
         TEST_CASE(localvarUnion1);
 
         TEST_CASE(localvarOp);          // Usage with arithmetic operators
@@ -5666,6 +5667,16 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:3:12]: (style) Variable 'x[0].a' is assigned a value that is never used. [unreadVariable]\n", errout_str());
     }
 
+    void localvarOverloadedSubscript() {
+        functionVariableUsage("struct A { B &operator [](size_t i); }\n"
+                              "struct B { int x; };\n"
+                              "void f(B *b) {\n"
+                              "    A a(b);\n"
+                              "    a[0].b = 0;\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout_str());
+    }
+
     void localvarUnion1() {
         // #9707
         functionVariableUsage("static short read(FILE *fp) {\n"