Merge pull request #19061 from michaelnebel/csharp/useless-assignment-to-local

C#: Add `cs/useless-assignment-to-local` to the code quality suite.

Author: michaelnebel

csharp/ql/src/codeql-suites/csharp-code-quality.qls

@@ -12,3 +12,4 @@
       - cs/constant-condition
       - cs/useless-gethashcode-call
       - cs/non-short-circuit
+      - cs/useless-assignment-to-local

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocal.cs

@@ -9,14 +9,14 @@ public class DeadStoreOfLocal
 
     public int M1()
     {
-        int x = M2(); // BAD
+        int x = M2(); // $ Alert
         return (x = 1) + x; // GOOD
     }
 
     public int M2()
     {
         int x = 1; // GOOD
-        return x + (x = 1); // BAD
+        return x + (x = 1); // $ Alert
     }
 
     public int M3()
@@ -41,19 +41,19 @@ public int M4()
 
     public void M5()
     {
-        int x = M3(); // BAD
+        int x = M3(); // $ Alert
     }
 
     public void M6()
     {
         int x = 42;
-        x += 1; // BAD
+        x += 1; // $ Alert
     }
 
     public void M7()
     {
         int x = 42;
-        x++; // BAD
+        x++; // $ Alert
     }
 
     public IEnumerable<string> M8(IEnumerable<string> source)
@@ -79,8 +79,8 @@ public IEnumerable<string> M9(IEnumerable<string> source)
 
     public void M10(IEnumerable<string> source)
     {
-        foreach (var val in source)
-        { // BAD
+        foreach (var val in source) // $ Alert
+        {
         }
     }
 }
@@ -98,10 +98,10 @@ public void F()
             message = "Unsuccessful completion";  // GOOD: Used in finally
             Process();
             info2 = "Finishing";                  // GOOD: Used in exception handler
-            extra = "Dead store here";            // BAD: Dead store
+            extra = "Dead store here";            // $ Alert Dead store
             Process();
             message = "Successful completion";    // GOOD: Used in finally
-            info1 = "Used in handler";            // BAD: Used in handler, but not a reachable handler
+            info1 = "Used in handler";            // $ Alert Used in handler, but not a reachable handler
         }
         catch (SystemException ex)
         {
@@ -139,7 +139,7 @@ public void FinallyFlow2()
         {
             Process();
         }
-        catch (Exception ex) // BAD
+        catch (Exception ex) // $ Alert
         {
             Console.WriteLine("Stage " + stage);
             stage = 3;  // GOOD: Used in finally
@@ -157,7 +157,7 @@ public class OutParam
     public void Test()
     {
         int x;
-        Fn(out x); // BAD
+        Fn(out x); // $ MISSING: Alert
         Fn(out _); // GOOD
     }
 
@@ -194,7 +194,7 @@ void M1()
 
     void M2()
     {
-        var x = M6(); // BAD [FALSE NEGATIVE]
+        var x = M6(); // $ MISSING: Alert
         Action a = () =>
         {
             x = 1; // GOOD
@@ -208,7 +208,7 @@ void M3()
         int x;
         Action a = () =>
         {
-            x = 1; // BAD [FALSE NEGATIVE]
+            x = 1; // $ MISSING: Alert
         };
         a();
     }
@@ -230,7 +230,7 @@ void M4()
 
     void M5()
     {
-        int x = 0; // BAD: NOT DETECTED
+        int x = 0; // $ MISSING: Alert
         Action a = () =>
         {
             x = 1; // GOOD
@@ -243,22 +243,22 @@ int M6()
     {
         fn(() =>
         {
-            int y = M6(); // BAD
+            int y = M6(); // $ Alert
             return (y = 1) + y; // GOOD
         });
 
         int captured = 0; // GOOD: Variable captured variable
         fn(() => { return captured; });
 
-        return captured = 1; // BAD: NOT DETECTED
+        return captured = 1; // $ MISSING: Alert
     }
 
     void M7()
     {
         var y = 12; // GOOD: Not a dead store (used in delegate)
         fn(() =>
         {
-            var x = y;  // BAD: Dead store in lambda
+            var x = y;  // $ Alert Dead store in lambda
             return 0;
         });
     }
@@ -297,8 +297,8 @@ void Test()
         { // GOOD
             Console.WriteLine($"int {i1}");
         }
-        else if (o is var v1)
-        { // BAD
+        else if (o is var v1) // $ Alert
+        {
         }
 
         switch (o)
@@ -311,7 +311,7 @@ void Test()
             case int i3: // GOOD
                 Console.WriteLine($"int {i3}");
                 break;
-            case var v2: // BAD
+            case var v2: // $ Alert
                 break;
             default:
                 Console.WriteLine("Something else");
@@ -328,7 +328,7 @@ void M()
         Use(x);
         Use(b);
         Use(s);
-        (x, (b, s)) = GetTuple(); // BAD: `b`
+        (x, (b, s)) = GetTuple(); // $ Alert on `b`
         Use(x);
         Use(s);
         (x, (_, s)) = GetTuple(); // GOOD
@@ -369,7 +369,7 @@ string M3()
 
     string M4()
     {
-        var s = M3(); // BAD
+        var s = M3(); // $ Alert
         s = "";
         return s;
     }
@@ -395,7 +395,7 @@ string M7(bool b)
     {
         var s = "";
         if (b)
-            s = "abc"; // BAD
+            s = "abc"; // $ Alert
         if (!b)
             return s;
         return null;
@@ -469,8 +469,18 @@ public static void M()
         using var x = new System.IO.FileStream("", System.IO.FileMode.Open); // GOOD
         using var _ = new System.IO.FileStream("", System.IO.FileMode.Open); // GOOD
 
-        using (var y = new System.IO.FileStream("", System.IO.FileMode.Open)) // BAD
+        using (var y = new System.IO.FileStream("", System.IO.FileMode.Open)) // $ Alert
         {
         }
     }
-}
+}
+
+class StringInterpolation
+{
+    void Pi()
+    {
+        float pi = 3.14159f; // GOOD
+        const int align = 6; // GOOD
+        Console.WriteLine($"Pi, {pi,align:F3}");
+    }
+}

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocal.qlref

@@ -1 +1,2 @@
-Dead Code/DeadStoreOfLocal.ql
+query: Dead Code/DeadStoreOfLocal.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocalBad.cs

@@ -4,7 +4,7 @@ class Bad
 {
     double ParseInt(string s)
     {
-        var success = int.TryParse(s, out int i);
+        var success = int.TryParse(s, out int i); // $ Alert
         return i;
     }
 
@@ -20,7 +20,7 @@ double ParseDouble(string s)
         {
             return double.Parse(s);
         }
-        catch (FormatException e)
+        catch (FormatException e) // $ Alert
         {
             return double.NaN;
         }
@@ -29,14 +29,14 @@ double ParseDouble(string s)
     int Count(string[] ss)
     {
         int count = 0;
-        foreach (var s in ss)
+        foreach (var s in ss) // $ Alert
             count++;
         return count;
     }
 
     string IsInt(object o)
     {
-        if (o is int i)
+        if (o is int i) // $ Alert
             return "yes";
         else
             return "no";
@@ -46,7 +46,7 @@ string IsString(object o)
     {
         switch (o)
         {
-            case string s:
+            case string s: // $ Alert
                 return "yes";
             default:
                 return "no";