C#: Allow attributes on local functions

Author: tamasvajk

csharp/change-notes/2020-11-18-local-function-attributable.md

@@ -0,0 +1,2 @@
+lgtm,codescanning
+* The `LocalFunction` class now extends `Attributable`. This is a C# 9 change.

csharp/ql/src/semmle/code/csharp/Attribute.qll

@@ -10,7 +10,8 @@ private import TypeRef
  * An element that can have attributes. Either an assembly (`Assembly`), a field (`Field`),
  * a parameter (`Parameter`), an operator (`Operator`), a method (`Method`), a constructor (`Constructor`),
  * a destructor (`Destructor`), a callable accessor (`CallableAccessor`), a value or reference type
- * (`ValueOrRefType`), or a declaration with accessors (`DeclarationWithAccessors`).
+ * (`ValueOrRefType`), a declaration with accessors (`DeclarationWithAccessors`), or a local function
+ * (`LocalFunction`).
  */
 class Attributable extends @attributable {
   /** Gets an attribute attached to this element, if any. */

csharp/ql/src/semmle/code/csharp/Callable.qll

@@ -972,7 +972,7 @@ class ExplicitConversionOperator extends ConversionOperator {
  * }
  * ```
  */
-class LocalFunction extends Callable, Modifiable, @local_function {
+class LocalFunction extends Callable, Modifiable, Attributable, @local_function {
   override string getName() { local_functions(this, result, _, _) }
 
   override LocalFunction getUnboundDeclaration() { local_functions(this, _, _, result) }
@@ -996,4 +996,6 @@ class LocalFunction extends Callable, Modifiable, @local_function {
   override Parameter getRawParameter(int i) { result = getParameter(i) }
 
   override string getAPrimaryQlClass() { result = "LocalFunction" }
+
+  override string toString() { result = Callable.super.toString() }
 }

csharp/ql/src/semmlecode.csharp.dbscheme

@@ -227,7 +227,8 @@ tokens(
 @external_element = @externalMetric | @externalDefect | @externalDataElement;
 
 @attributable = @assembly | @field | @parameter | @operator | @method | @constructor
-              | @destructor | @callable_accessor | @value_or_ref_type | @declaration_with_accessors;
+              | @destructor | @callable_accessor | @value_or_ref_type | @declaration_with_accessors
+              | @local_function;
 
 /** LOCATIONS, ASEMMBLIES, MODULES, FILES and FOLDERS **/
 
@@ -986,7 +987,7 @@ case @expr.kind of
 | 109 = @local_function_invocation_expr
 | 110 = @ref_expr
 | 111 = @discard_expr
-/* C# 8.0 */ 
+/* C# 8.0 */
 | 112 = @range_expr
 | 113 = @index_expr
 | 114 = @switch_expr

csharp/ql/test/library-tests/csharp9/LocalFunction.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Threading.Tasks;
 
-public class Class1
+public class LocalFunction
 {
     public async Task M1()
     {
@@ -15,4 +15,15 @@ public async Task M1()
 
         static extern void localExtern();
     }
+
+    public void M2()
+    {
+        [Obsolete]
+        int? dup([System.Diagnostics.CodeAnalysis.NotNullWhen(true)] bool b, int? i)
+        {
+            return 2 * i;
+        }
+
+        dup(true, 42);
+    }
 }

csharp/ql/test/library-tests/csharp9/LocalFunctions.expected

@@ -6,3 +6,6 @@ localFunctionModifier
 | LocalFunction.cs:16:9:16:41 | localExtern | extern |
 | LocalFunction.cs:16:9:16:41 | localExtern | private |
 | LocalFunction.cs:16:9:16:41 | localExtern | static |
+| LocalFunction.cs:21:9:25:9 | dup | private |
+localFunctionAttribute
+| LocalFunction.cs:21:9:25:9 | dup | LocalFunction.cs:21:10:21:17 | [Obsolete(...)] |

csharp/ql/test/library-tests/csharp9/LocalFunctions.ql

@@ -5,3 +5,5 @@ query predicate noBody(LocalFunction lf) { not lf.hasBody() }
 query predicate localFunctionModifier(LocalFunction lf, string modifier) {
   lf.hasModifier(modifier)
 }
+
+query predicate localFunctionAttribute(LocalFunction lf, Attribute a) { a = lf.getAnAttribute() }

csharp/ql/test/library-tests/csharp9/PrintAst.expected

@@ -48,7 +48,7 @@ Discard.cs:
 #   10|               0: [ReturnStmt] return ...;
 #   10|                 0: [IntLiteral] 0
 LocalFunction.cs:
-#    4| [Class] Class1
+#    4| [Class] LocalFunction
 #    6|   5: [Method] M1
 #    6|     -1: [TypeMention] Task
 #    7|     4: [BlockStmt] {...}
@@ -77,6 +77,36 @@ LocalFunction.cs:
 #   14|             0: [IntLiteral] 2
 #   16|       3: [LocalFunctionStmt] localExtern(...)
 #   16|         0: [LocalFunction] localExtern
+#   19|   6: [Method] M2
+#   19|     -1: [TypeMention] Void
+#   20|     4: [BlockStmt] {...}
+#   21|       0: [LocalFunctionStmt] dup(...)
+#   21|         0: [LocalFunction] dup
+#-----|           0: (Attributes)
+#   21|             1: [Attribute] [Obsolete(...)]
+#   21|               0: [TypeMention] ObsoleteAttribute
+#-----|           2: (Parameters)
+#   22|             0: [Parameter] b
+#   22|               -1: [TypeMention] bool
+#-----|               0: (Attributes)
+#   22|                 1: [Attribute] [NotNullWhen(...)]
+#   22|                   -1: [TypeMention] NotNullWhenAttribute
+#   22|                   0: [BoolLiteral] true
+#   22|             1: [Parameter] i
+#   22|               -1: [TypeMention] int?
+#   22|                 1: [TypeMention] int
+#   23|           4: [BlockStmt] {...}
+#   24|             0: [ReturnStmt] return ...;
+#   24|               0: [MulExpr] ... * ...
+#   24|                 0: [CastExpr] (...) ...
+#   24|                   1: [IntLiteral] 2
+#   24|                 1: [ParameterAccess] access to parameter i
+#   27|       1: [ExprStmt] ...;
+#   27|         0: [LocalFunctionCall] call to local function dup
+#   27|           -1: [LocalFunctionAccess] access to local function dup
+#   27|           0: [BoolLiteral] true
+#   27|           1: [CastExpr] (...) ...
+#   27|             1: [IntLiteral] 42
 NativeInt.cs:
 #    3| [Class] NativeInt
 #    5|   5: [Method] M1

csharp/upgrades/TO_CHANGE/upgrade.properties

@@ -0,0 +1,2 @@
+description: Added 'local_function' to 'attributable'.
+compatibility: backwards