IdentifierHidden: improve lambda handling case

Author: knewbury01

cpp/common/src/codingstandards/cpp/rules/identifierhidden/IdentifierHidden.qll

@@ -6,11 +6,22 @@ import cpp
 import codingstandards.cpp.Customizations
 import codingstandards.cpp.Exclusions
 import codingstandards.cpp.Scope
+import codingstandards.cpp.ConstHelpers
 
 abstract class IdentifierHiddenSharedQuery extends Query { }
 
 Query getQuery() { result instanceof IdentifierHiddenSharedQuery }
 
+/**
+ * a `IntegralOrEnumType` that is nonvolatile and const
+ */
+class NonVolatileConstIntegralOrEnumType extends IntegralOrEnumType {
+  NonVolatileConstIntegralOrEnumType() {
+    not this.isVolatile() and
+    this.isConst()
+  }
+}
+
 /**
  * Holds if declaration `innerDecl`, declared in a lambda, hides a declaration `outerDecl` captured by the lambda.
  */
@@ -19,10 +30,35 @@ predicate hiddenInLambda(UserVariable outerDecl, UserVariable innerDecl) {
     //innerDecl declared inside of the lambda
     s.getADeclaration() = innerDecl and
     s.getAnAncestor() = le and
-    le.getEnclosingFunction().getBasicBlock().(Scope) = outerDecl.getParentScope() and
-    exists(LambdaCapture cap |
-      outerDecl.getAnAccess() = cap.getInitializer().(VariableAccess) and
-      le.getLambdaExpression().getACapture() = cap
+    //a variable can be accessed (therefore hide) another when:
+    //it is explicitly captured
+    (
+      exists(LambdaCapture cap |
+        outerDecl.getAnAccess() = cap.getInitializer().(VariableAccess) and
+        le.getLambdaExpression().getACapture() = cap and
+        //captured variable (outerDecl) is in the same (function) scope as the lambda itself
+        outerDecl.getParentScope() = le.getEnclosingFunction().getBasicBlock().(Scope)
+      )
+      or
+      //is non-local
+      outerDecl instanceof GlobalVariable
+      or
+      //has static or thread local storage duration
+      (outerDecl.isThreadLocal() or outerDecl.isStatic())
+      or
+      //is a reference that has been initialized with a constant expression.
+      outerDecl.getType().stripTopLevelSpecifiers() instanceof ReferenceType and
+      exists(outerDecl.getInitializer().getExpr().getValue())
+      or
+      //const non-volatile integral or enumeration type and has been initialized with a constant expression
+      outerDecl.getType() instanceof NonVolatileConstIntegralOrEnumType and
+      exists(outerDecl.getInitializer().getExpr().getValue())
+      or
+      //is constexpr and has no mutable members
+      outerDecl.isConstexpr() and
+      not exists(Class c |
+        c = outerDecl.getType() and not c.getAMember() instanceof MutableVariable
+      )
     ) and
     innerDecl.getName() = outerDecl.getName()
   )

cpp/common/test/rules/identifierhidden/IdentifierHidden.expected

@@ -10,3 +10,4 @@
 | test.cpp:75:16:75:16 | i | Declaration is hiding declaration $@. | test.cpp:61:7:61:7 | i | i |
 | test.cpp:81:5:81:5 | a | Declaration is hiding declaration $@. | test.cpp:79:5:79:5 | a | a |
 | test.cpp:102:9:102:9 | b | Declaration is hiding declaration $@. | test.cpp:96:11:96:11 | b | b |
+| test.cpp:114:9:114:17 | globalvar | Declaration is hiding declaration $@. | test.cpp:110:5:110:13 | globalvar | globalvar |

cpp/common/test/rules/identifierhidden/test.cpp

@@ -105,4 +105,18 @@ void f4() {
 }
 
 void f5(int i) {}    // COMPLIANT - exception - assume purposefully overloaded
-void f5(double d) {} // COMPLIANT - exception - assume purposefully overloaded
+void f5(double d) {} // COMPLIANT - exception - assume purposefully overloaded
+
+int globalvar = 0;
+
+int f6() {
+  auto lambda_with_shadowing = []() {
+    int globalvar = 1; // NON_COMPLIANT - not an exception - not captured but
+                       // still accessible
+    return globalvar + globalvar;
+  };
+
+  auto lambda_without_shadowing = []() { return globalvar + globalvar; };
+
+  return lambda_with_shadowing();
+}