C#: Extract modifiers for lambdas (async, static)

Author: tamasvajk

csharp/change-notes/2020-11-18-lambda-modifiers.md

@@ -0,0 +1,2 @@
+lgtm,codescanning
+* The `AnonymousFunctionExpr` class now extends `Modifiable`. This change allows storing the `async` modifier for lambdas, which was missing before, and the `static` modifier, which was added in C# 9.

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Lambda.cs

@@ -24,6 +24,18 @@ private void VisitParameter(ParameterSyntax p)
         private Lambda(ExpressionNodeInfo info, CSharpSyntaxNode body, IEnumerable<ParameterSyntax> @params)
             : base(info)
         {
+            var symbol = cx.GetModel(info.Node).GetSymbolInfo(info.Node).Symbol as IMethodSymbol;
+
+            if (symbol is object)
+            {
+                Modifier.ExtractStaticModifier(cx, info.Context.TrapWriter.Writer, this, symbol);
+                Modifier.ExtractAsyncModifier(cx, info.Context.TrapWriter.Writer, this, symbol);
+            }
+            else
+            {
+                cx.ModelError(info.Node, "Unknown declared symbol");
+            }
+
             // No need to use `Populate` as the population happens later
             cx.PopulateLater(() =>
             {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Modifier.cs

@@ -86,10 +86,7 @@ public static void ExtractModifiers(Context cx, TextWriter trapFile, IEntity key
             if (symbol.IsSealed)
                 HasModifier(cx, trapFile, key, "sealed");
 
-            var fromSource = symbol.DeclaringSyntaxReferences.Length > 0;
-
-            if (symbol.IsStatic && !(symbol.Kind == SymbolKind.Field && ((IFieldSymbol)symbol).IsConst && !fromSource))
-                HasModifier(cx, trapFile, key, "static");
+            ExtractStaticModifier(cx, trapFile, key, symbol);
 
             if (symbol.IsVirtual)
                 HasModifier(cx, trapFile, key, "virtual");
@@ -104,8 +101,7 @@ public static void ExtractModifiers(Context cx, TextWriter trapFile, IEntity key
             if (symbol.IsOverride)
                 HasModifier(cx, trapFile, key, "override");
 
-            if (symbol.Kind == SymbolKind.Method && ((IMethodSymbol)symbol).IsAsync)
-                HasModifier(cx, trapFile, key, "async");
+            ExtractAsyncModifier(cx, trapFile, key, symbol);
 
             if (symbol.IsExtern)
                 HasModifier(cx, trapFile, key, "extern");
@@ -129,6 +125,20 @@ public static void ExtractModifiers(Context cx, TextWriter trapFile, IEntity key
             }
         }
 
+        public static void ExtractAsyncModifier(Context cx, TextWriter trapFile, IEntity key, ISymbol symbol)
+        {
+            if (symbol.Kind == SymbolKind.Method && ((IMethodSymbol)symbol).IsAsync)
+                HasModifier(cx, trapFile, key, "async");
+        }
+
+        public static void ExtractStaticModifier(Context cx, TextWriter trapFile, IEntity key, ISymbol symbol)
+        {
+            var fromSource = symbol.DeclaringSyntaxReferences.Length > 0;
+
+            if (symbol.IsStatic && !(symbol.Kind == SymbolKind.Field && ((IFieldSymbol)symbol).IsConst && !fromSource))
+                HasModifier(cx, trapFile, key, "static");
+        }
+
         public static Modifier Create(Context cx, string modifier)
         {
             return ModifierFactory.Instance.CreateEntity(cx, (typeof(Modifier), modifier), modifier);

csharp/ql/src/semmle/code/csharp/exprs/Creation.qll

@@ -407,7 +407,7 @@ class Stackalloc extends ArrayCreation {
  * An anonymous function. Either a lambda expression (`LambdaExpr`) or an
  * anonymous method expression (`AnonymousMethodExpr`).
  */
-class AnonymousFunctionExpr extends Expr, Callable, @anonymous_function_expr {
+class AnonymousFunctionExpr extends Expr, Callable, Modifiable, @anonymous_function_expr {
   override string getName() { result = "<anonymous>" }
 
   override Type getReturnType() {

csharp/ql/src/semmlecode.csharp.dbscheme

@@ -541,7 +541,7 @@ specific_type_parameter_nullability(
 
 @modifiable = @modifiable_direct | @event_accessor;
 
-@modifiable_direct = @member | @accessor | @local_function;
+@modifiable_direct = @member | @accessor | @local_function | @anonymous_function_expr;
 
 modifiers(
   unique int id: @modifier,

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

@@ -6,3 +6,6 @@
 | Discard.cs:9:13:9:32 | (...) => ... | Discard.cs:9:25:9:25 | _`1 |
 | Discard.cs:10:13:10:49 | delegate(...) { ... } | Discard.cs:10:27:10:27 | _ |
 | Discard.cs:10:13:10:49 | delegate(...) { ... } | Discard.cs:10:34:10:34 | _`1 |
+| LambdaModifier.cs:11:11:11:27 | (...) => ... | LambdaModifier.cs:11:18:11:18 | x |
+| LambdaModifier.cs:12:11:12:20 | (...) => ... | LambdaModifier.cs:12:11:12:11 | x |
+| LambdaModifier.cs:13:11:13:51 | delegate(...) { ... } | LambdaModifier.cs:13:32:13:32 | x |

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

@@ -0,0 +1,17 @@
+using System;
+using System.Threading.Tasks;
+
+public class Class1
+{
+    public async Task M1()
+    {
+        void m(Func<int, int> f) { }
+
+        const int z = 10;
+        m(static x => x + z);
+        m(x => x + z);
+        m(static delegate (int x) { return x + z; });
+
+        await Task.Run(async () => { await Task.CompletedTask; });
+    }
+}

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

@@ -0,0 +1,3 @@
+| LambdaModifier.cs:11:11:11:27 | (...) => ... | static |
+| LambdaModifier.cs:13:11:13:51 | delegate(...) { ... } | static |
+| LambdaModifier.cs:15:24:15:64 | (...) => ... | async |

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

@@ -0,0 +1,5 @@
+import csharp
+
+from AnonymousFunctionExpr anon, string modifier
+where anon.hasModifier(modifier)
+select anon, modifier

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

@@ -1,6 +1,7 @@
 noBody
 | LocalFunction.cs:16:9:16:41 | localExtern |
 localFunctionModifier
+| LambdaModifier.cs:8:9:8:36 | m | private |
 | LocalFunction.cs:9:9:12:9 | mul | async |
 | LocalFunction.cs:9:9:12:9 | mul | private |
 | LocalFunction.cs:16:9:16:41 | localExtern | extern |