Merge pull request #8152 from tamasvajk/fix/useless-dynamic-cast

tamasvajk · web-flow · commit d3e36038a02b · 2022-02-28T17:00:28.000+01:00
C# Exclude dynamic casts from useless casts check
diff --git a/csharp/ql/src/Language Abuse/UselessUpcast.ql b/csharp/ql/src/Language Abuse/UselessUpcast.ql
@@ -204,6 +204,8 @@ class ExplicitUpcast extends ExplicitCast {
     this = any(LocalVariableDeclAndInitExpr decl | decl.isImplicitlyTyped()).getInitializer()
     or
     exists(LambdaExpr c | c.canReturn(this))
+    or
+    dest instanceof DynamicType
   }
 }
 
diff --git a/csharp/ql/src/change-notes/2022-02-28-useless-upcast.md b/csharp/ql/src/change-notes/2022-02-28-useless-upcast.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Casts to `dynamic` are excluded from the useless upcasts check (`cs/useless-upcast`).
diff --git a/csharp/ql/test/query-tests/Language Abuse/UselessUpcast/UselessUpcast.cs b/csharp/ql/test/query-tests/Language Abuse/UselessUpcast/UselessUpcast.cs
@@ -17,8 +17,8 @@ public void M(A a) { }
 
 class B : A
 {
-    public static bool operator==(B b1, B b2) { return false; }
-    public static bool operator!=(B b1, B b2) { return true; }
+    public static bool operator ==(B b1, B b2) { return false; }
+    public static bool operator !=(B b1, B b2) { return true; }
     public void M(B b) { }
 }
 
@@ -68,11 +68,11 @@ void Test1(string[] args)
 
         ((I2)a).Foo(); // GOOD: Cast to an interface
 
-        o = a==(A)b; // GOOD: EQExpr
+        o = a == (A)b; // GOOD: EQExpr
 
-        o = b==(B)b; // GOOD: Operator call
+        o = b == (B)b; // GOOD: Operator call
 
-        var act = (Action) (() => { }); // GOOD
+        var act = (Action)(() => { }); // GOOD
 
         var objects = args.Select(arg => (object)arg); // GOOD
 
@@ -126,9 +126,9 @@ public static void M2(this I3 i) =>
 
 static class StaticMethods
 {
-   public static void M1(A _) { }
-   public static void M1(B _) { }
-   public static void M2(B _) { }
+    public static void M1(A _) { }
+    public static void M1(B _) { }
+    public static void M2(B _) { }
 }
 
 class Constructors : I2
@@ -162,4 +162,12 @@ void M(SubSub ss)
             new Sub((Sub)ss); // BAD
         }
     }
+
+    class Dynamic
+    {
+        void M(object o)
+        {
+            var s0 = ((dynamic)o).ToString(); // GOOD
+        }
+    }
 }

Original file line number	Diff line number	Diff line change
`@@ -204,6 +204,8 @@ class ExplicitUpcast extends ExplicitCast {`
`204`	`204`	`this = any(LocalVariableDeclAndInitExpr decl \| decl.isImplicitlyTyped()).getInitializer()`
`205`	`205`	`or`
`206`	`206`	`exists(LambdaExpr c \| c.canReturn(this))`
	`207`	`+ or`
	`208`	`+ dest instanceof DynamicType`
`207`	`209`	`}`
`208`	`210`	`}`
`209`	`211`
-Original file line number
+Diff line change
@@ @@ -0,0 +1,4 @@ @@
 +---
 +category: minorAnalysis
 +---
 +* Casts to `dynamic` are excluded from the useless upcasts check (`cs/useless-upcast`).
Original file line number	Diff line number	Diff line change
`@@ -17,8 +17,8 @@ public void M(A a) { }`
`17`	`17`
`18`	`18`	`class B : A`
`19`	`19`	`{`
`20`		`- public static bool operator==(B b1, B b2) { return false; }`
`21`		`- public static bool operator!=(B b1, B b2) { return true; }`
	`20`	`+ public static bool operator ==(B b1, B b2) { return false; }`
	`21`	`+ public static bool operator !=(B b1, B b2) { return true; }`
`22`	`22`	`public void M(B b) { }`
`23`	`23`	`}`
`24`	`24`
`@@ -68,11 +68,11 @@ void Test1(string[] args)`
`68`	`68`
`69`	`69`	`((I2)a).Foo(); // GOOD: Cast to an interface`
`70`	`70`
`71`		`- o = a==(A)b; // GOOD: EQExpr`
	`71`	`+ o = a == (A)b; // GOOD: EQExpr`
`72`	`72`
`73`		`- o = b==(B)b; // GOOD: Operator call`
	`73`	`+ o = b == (B)b; // GOOD: Operator call`
`74`	`74`
`75`		`- var act = (Action) (() => { }); // GOOD`
	`75`	`+ var act = (Action)(() => { }); // GOOD`
`76`	`76`
`77`	`77`	`var objects = args.Select(arg => (object)arg); // GOOD`
`78`	`78`
`@@ -126,9 +126,9 @@ public static void M2(this I3 i) =>`
`126`	`126`
`127`	`127`	`static class StaticMethods`
`128`	`128`	`{`
`129`		`- public static void M1(A _) { }`
`130`		`- public static void M1(B _) { }`
`131`		`- public static void M2(B _) { }`
	`129`	`+ public static void M1(A _) { }`
	`130`	`+ public static void M1(B _) { }`
	`131`	`+ public static void M2(B _) { }`
`132`	`132`	`}`
`133`	`133`
`134`	`134`	`class Constructors : I2`
`@@ -162,4 +162,12 @@ void M(SubSub ss)`
`162`	`162`	`new Sub((Sub)ss); // BAD`
`163`	`163`	`}`
`164`	`164`	`}`
	`165`	`+`
	`166`	`+ class Dynamic`
	`167`	`+ {`
	`168`	`+ void M(object o)`
	`169`	`+ {`
	`170`	`+ var s0 = ((dynamic)o).ToString(); // GOOD`
	`171`	`+ }`
	`172`	`+ }`
`165`	`173`	`}`