Merge pull request github#1925 from geoffw0/qldoceg10

CPP: Add syntax examples to QLDoc in Access.qll, Declaration.qll

Author: zlaski-semmle

cpp/ql/src/semmle/code/cpp/Declaration.qll

@@ -14,8 +14,12 @@ private import semmle.code.cpp.internal.QualifiedName as Q
  * ```
  *   extern int myglobal;
  * ```
- * Each of these declarations is given its own distinct `DeclarationEntry`,
- * but they all share the same `Declaration`.
+ * and defined in one:
+ * ```
+ *   int myglobal;
+ * ```
+ * Each of these declarations (including the definition) is given its own
+ * distinct `DeclarationEntry`, but they all share the same `Declaration`.
  *
  * Some derived class of `Declaration` do not have a corresponding
  * `DeclarationEntry`, because they always have a unique source ___location.
@@ -206,9 +210,19 @@ abstract class Declaration extends Locatable, @declaration {
 }
 
 /**
- * A C/C++ declaration entry. See the comment above `Declaration` for an
- * explanation of the relationship between `Declaration` and
- * `DeclarationEntry`.
+ * A C/C++ declaration entry. For example the following code contains five
+ * declaration entries:
+ * ```
+ * extern int myGlobal;
+ * int myVariable;
+ * typedef char MyChar;
+ * void myFunction();
+ * void myFunction() {
+ *   // ...
+ * }
+ * ```
+ * See the comment above `Declaration` for an explanation of the relationship
+ * between `Declaration` and `DeclarationEntry`.
  */
 abstract class DeclarationEntry extends Locatable {
   /** Gets a specifier associated with this declaration entry. */
@@ -281,8 +295,19 @@ abstract class DeclarationEntry extends Locatable {
  * A declaration that can potentially have more C++ access rights than its
  * enclosing element. This comprises `Class` (they have access to their own
  * private members) along with other `UserType`s and `Function` (they can be
- * the target of `friend` declarations).
+ * the target of `friend` declarations).  For example `MyClass` and
+ * `myFunction` in the following code:
+ * ```
+ * class MyClass
+ * {
+ * public:
+ *   ...
+ * };
  *
+ * void myFunction() {
+ *   // ...
+ * }
+ * ```
  * In the C++ standard (N4140 11.2), rules for access control revolve around
  * the informal phrase "_R_ occurs in a member or friend of class C", where
  * `AccessHolder` corresponds to this _R_.
@@ -416,8 +441,19 @@ abstract class AccessHolder extends Declaration {
 /**
  * A declaration that very likely has more C++ access rights than its
  * enclosing element. This comprises `Class` (they have access to their own
- * private members) along with any target of a `friend` declaration.
+ * private members) along with any target of a `friend` declaration.  For
+ * example `MyClass` and `friendFunction` in the following code:
+ * ```
+ * class MyClass
+ * {
+ * public:
+ *   friend void friendFunction();
+ * };
  *
+ * void friendFunction() {
+ *   // ...
+ * }
+ * ```
  * Most access rights are computed for `DirectAccessHolder` instead of
  * `AccessHolder` -- that's more efficient because there are fewer
  * `DirectAccessHolder`s. If a `DirectAccessHolder` contains an `AccessHolder`,

cpp/ql/src/semmle/code/cpp/exprs/Access.qll

@@ -18,7 +18,18 @@ abstract class Access extends Expr, NameQualifiableElement {
 }
 
 /**
- * A C/C++ enum constant access expression.
+ * A C/C++ `enum` constant access expression. For example the access to
+ * `MYENUMCONST1` in `myFunction` in the following code:
+ * ```
+ * enum MyEnum {
+ *   MYENUMCONST1,
+ *   MYENUMCONST2
+ * };
+ *
+ * void myFunction() {
+ *   MyEnum v = MYENUMCONST1;
+ * };
+ * ```
  */
 class EnumConstantAccess extends Access, @varaccess {
   override string getCanonicalQLClass() { result = "EnumConstantAccess" }
@@ -27,15 +38,23 @@ class EnumConstantAccess extends Access, @varaccess {
     exists(EnumConstant c | varbind(underlyingElement(this), unresolveElement(c)))
   }
 
-  /** Gets the accessed enum constant. */
+  /** Gets the accessed `enum` constant. */
   override EnumConstant getTarget() { varbind(underlyingElement(this), unresolveElement(result)) }
 
-  /** Gets a textual representation of this enum constant access. */
+  /** Gets a textual representation of this `enum` constant access. */
   override string toString() { result = this.getTarget().getName() }
 }
 
 /**
- * A C/C++ variable access expression.
+ * A C/C++ variable access expression. For example the accesses to
+ * `x` and `y` in `myFunction` in the following code:
+ * ```
+ * int x;
+ *
+ * void myFunction(int y) {
+ *   x = y;
+ * };
+ * ```
  */
 class VariableAccess extends Access, @varaccess {
   override string getCanonicalQLClass() { result = "VariableAccess" }
@@ -129,7 +148,18 @@ class VariableAccess extends Access, @varaccess {
 }
 
 /**
- * A C/C++ field access expression.
+ * A C/C++ field access expression. For example the accesses to
+ * `x` and `y` in `myMethod` in the following code:
+ * ```
+ * class MyClass {
+ * public:
+ *   void myMethod(MyClass &other) {
+ *     x = other.y;
+ *   }
+ *
+ *   int x, y;
+ * };
+ * ```
  */
 class FieldAccess extends VariableAccess {
   override string getCanonicalQLClass() { result = "FieldAccess" }
@@ -141,8 +171,23 @@ class FieldAccess extends VariableAccess {
 }
 
 /**
- * A field access of the form `obj->field`. The type of `obj` is a pointer,
- * so this is equivalent to `(*obj).field`.
+ * A field access whose qualifier is a pointer to a class, struct or union.
+ * These typically take the form `obj->field`. Another case is a field access
+ * with an implicit `this->` qualifier, which is often a `PointerFieldAccess`
+ * (but see also `ImplicitThisFieldAccess`).
+ *
+ * For example the accesses to `x` and `y` in `myMethod` in the following code
+ * are each a `PointerFieldAccess`:
+ * ```
+ * class MyClass {
+ * public:
+ *   void myMethod(MyClass *other) {
+ *       other->x = y;
+ *   }
+ *
+ *   int x, y;
+ * };
+ * ```
  */
 class PointerFieldAccess extends FieldAccess {
   override string getCanonicalQLClass() { result = "PointerFieldAccess" }
@@ -169,7 +214,18 @@ class DotFieldAccess extends FieldAccess {
 
 /**
  * A field access of the form `obj.field`, where the type of `obj` is a
- * reference to a class/struct/union.
+ * reference to a class/struct/union. For example the accesses to `y` in
+ * `myMethod` in the following code:
+ * ```
+ * class MyClass {
+ * public:
+ *   void myMethod(MyClass a, MyClass &b) {
+ *     a.x = b.y;
+ *   }
+ *
+ *   int x, y;
+ * };
+ * ```
  */
 class ReferenceFieldAccess extends DotFieldAccess {
   override string getCanonicalQLClass() { result = "ReferenceFieldAccess" }
@@ -179,7 +235,18 @@ class ReferenceFieldAccess extends DotFieldAccess {
 
 /**
  * A field access of the form `obj.field`, where the type of `obj` is a
- * class/struct/union (and not a reference).
+ * class/struct/union (and not a reference). For example the accesses to `x`
+ * in `myMethod` in the following code:
+ * ```
+ * class MyClass {
+ * public:
+ *   void myMethod(MyClass a, MyClass &b) {
+ *     a.x = b.y;
+ *   }
+ *
+ *   int x, y;
+ * };
+ * ```
  */
 class ValueFieldAccess extends DotFieldAccess {
   override string getCanonicalQLClass() { result = "ValueFieldAccess" }
@@ -198,25 +265,40 @@ private predicate referenceConversion(Conversion c) {
 /**
  * Holds if `e` is a reference expression (that is, it has a type of the
  * form `T&`), which is converted to a value. For example:
- *
  * ```
  * int myfcn(MyStruct &x) {
  *   return x.field;
  * }
  * ```
- *
  * In this example, the type of `x` is `MyStruct&`, but it gets implicitly
  * converted to `MyStruct` in the expression `x.field`.
  */
 private predicate exprHasReferenceConversion(Expr e) { referenceConversion(e.getConversion+()) }
 
 /**
- * A field access of a field of `this`. The access has no qualifier because
- * the use of `this` is implicit. For example, `field` is equivalent to
- * `this->field` if `field` is a member of `this`.
+ * A field access of a field of `this` which has no qualifier because
+ * the use of `this` is implicit. For example, in the following code the
+ * implicit call to the destructor of `A` has no qualifier because the
+ * use of `this` is implicit:
+ * ```
+ * class A {
+ * public:
+ *   ~A() {
+ *     // ...
+ *   }
+ * };
  *
+ * class B {
+ * public:
+ *   A a;
+ *
+ *   ~B() {
+ *     // Implicit call to the destructor of `A`.
+ *   }
+ * };
+ * ```
  * Note: the C++ front-end often automatically desugars `field` to
- * `this->field`, so most implicit accesses of `this->field` are instances
+ * `this->field`, so most accesses of `this->field` are instances
  * of `PointerFieldAccess` (with `ThisExpr` as the qualifier), not
  * `ImplicitThisFieldAccess`.
  */
@@ -250,7 +332,15 @@ class PointerToFieldLiteral extends ImplicitThisFieldAccess {
 }
 
 /**
- * A C/C++ function access expression.
+ * A C/C++ function access expression. For example the access to
+ * `myFunctionTarget` in `myFunction` in the following code:
+ * ```
+ * int myFunctionTarget(int);
+ *
+ * void myFunction() {
+ *   int (*myFunctionPointer)(int) = &myTarget;
+ * }
+ * ```
  */
 class FunctionAccess extends Access, @routineexpr {
   FunctionAccess() { not iscall(underlyingElement(this), _) }
@@ -269,7 +359,7 @@ class FunctionAccess extends Access, @routineexpr {
 }
 
 /**
- * An access to a parameter of a function signature for the purposes of a decltype.
+ * An access to a parameter of a function signature for the purposes of a `decltype`.
  *
  * For example, given the following code:
  * ```
@@ -279,15 +369,30 @@ class FunctionAccess extends Access, @routineexpr {
  *   }
  * ```
  * The return type of the function is a decltype, the expression of which contains
- * an add expression, which in turn has two ParamAccessForType children.
+ * an add expression, which in turn has two `ParamAccessForType` children.
  */
 class ParamAccessForType extends Expr, @param_ref {
   override string toString() { result = "param access" }
 }
 
 /**
  * An access to a type.  This occurs in certain contexts where a built-in
- * works on types directly rather than variables, expressions etc.
+ * works on types directly rather than variables, expressions etc.  For
+ * example the reference to `MyClass` in `__is_pod` in the following code:
+ * ```
+ * class MyClass {
+ *   ...
+ * };
+ *
+ * void myFunction() {
+ *   if (__is_pod(MyClass))
+ *   {
+ *     ...
+ *   } else {
+ *     ...
+ *   }
+ * }
+ * ```
  */
 class TypeName extends Expr, @type_operand {
   override string getCanonicalQLClass() { result = "TypeName" }
@@ -296,24 +401,32 @@ class TypeName extends Expr, @type_operand {
 }
 
 /**
- * A C/C++ array access expression.
+ * A C/C++ array access expression. For example, the access to `as` in
+ * `myFunction` in the following code:
+ * ```
+ * int as[10];
  *
- * For calls to operator[], which look syntactically identical, see OverloadedArrayExpr.
+ * void myFunction() {
+ *   as[0]++;
+ * }
+ * ```
+ * For calls to `operator[]`, which look syntactically identical, see
+ * `OverloadedArrayExpr`.
  */
 class ArrayExpr extends Expr, @subscriptexpr {
   override string getCanonicalQLClass() { result = "ArrayExpr" }
 
   /**
    * Gets the array or pointer expression being subscripted.
    *
-   * This is arr in both arr[0] and 0[arr].
+   * This is `arr` in both `arr[0]` and `0[arr]`.
    */
   Expr getArrayBase() { result = this.getChild(0) }
 
   /**
    * Gets the expression giving the index into the array.
    *
-   * This is 0 in both arr[0] and 0[arr].
+   * This is `0` in both `arr[0]` and `0[arr]`.
    */
   Expr getArrayOffset() { result = this.getChild(1) }
 

cpp/ql/src/semmle/code/cpp/stmts/Stmt.qll

@@ -1645,6 +1645,7 @@ class EnumSwitch extends SwitchStmt {
  * } catch (std::exception &e) {
  *   g();
  * }
+ * ```
  * there is a handler that's associated with the `catch` block and controls
  * entry to it.
  */

cpp/ql/test/library-tests/access/FieldAccess/FieldAccess.cpp

@@ -84,3 +84,34 @@ int test_val00(S s) {
 int test_val01(U u) {
   return u.x;
 }
+
+class MyClass {
+public:
+  void myMethod(MyClass a, MyClass &b, MyClass *c) {
+    a.x = b.y; // val, ref
+    c->x = y; // ptr, ptr
+    c->x = this->y; // ptr, ptr
+    (&b)->y = (*c).y; // ptr, val
+  }
+
+  int x, y;
+};
+
+class MyHasDestructor1 {
+public:
+  ~MyHasDestructor1() {
+    // ...
+  }
+};
+
+class MyHasDestructor2 {
+public:
+  int x;
+  MyHasDestructor1 v;
+
+  ~MyHasDestructor2() {
+    x++; // PointerFieldAccess, the `this->` is generated rather than implicit.
+
+    // ImplicitThisFieldAccess on call `v`s destructor.
+  }
+};