Merge pull request github#7758 from jketema/unnamed-variable-fix

C++: Do not report "Declaration hides variable" for unnamed variables

Author: MathiasVP

cpp/ql/src/Best Practices/Hiding/DeclarationHidesVariable.ql

@@ -18,6 +18,7 @@ where
   not lv1.isCompilerGenerated() and
   not lv2.isCompilerGenerated() and
   not lv1.getParentScope().(BlockStmt).isInMacroExpansion() and
-  not lv2.getParentScope().(BlockStmt).isInMacroExpansion()
+  not lv2.getParentScope().(BlockStmt).isInMacroExpansion() and
+  not lv1.getName() = "(unnamed local variable)"
 select lv1, "Variable " + lv1.getName() + " hides another variable of the same name (on $@).", lv2,
   "line " + lv2.getLocation().getStartLine().toString()

cpp/ql/src/change-notes/2022-01-26-unnamed-variable-declaration-hiding.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Fix an issue with the `cpp/declaration-hides-variable` query where it would report variables that are unnamed in a database.

cpp/ql/test/query-tests/Best Practices/Hiding/DeclarationHidesVariable/hiding.cpp

@@ -1,4 +1,4 @@
-
+// semmle-extractor-options: -std=c++17
 void f(void) {
     if (1) {
         int i;
@@ -30,3 +30,12 @@ void nestedRangeBasedFor() {
     for (auto y : ys) // GOOD
       x = y = 0;
 }
+
+void structuredBinding() {
+  int xs[1] = {1};
+  auto [x] = xs;
+  {
+    auto [x] = xs; // BAD [NOT DETECTED]
+    auto [y] = xs; // GOOD
+  }
+}