Merge pull request github#18935 from michaelnebel/csharp/useless-if-statement

C#: Fewer alerts in `cs/useless-if-statement`.

Author: michaelnebel

csharp/ql/src/Useless code/FutileConditional.ql

@@ -16,7 +16,8 @@ predicate emptyStmt(Stmt s) {
   or
   s =
     any(BlockStmt bs |
-      bs.getNumberOfStmts() = 0
+      bs.getNumberOfStmts() = 0 and
+      not any(CommentBlock cb).getParent() = bs
       or
       bs.getNumberOfStmts() = 1 and
       emptyStmt(bs.getStmt(0))

csharp/ql/src/change-notes/2025-03-05-useless-if-statement.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Don't consider an if-statement to be *useless* in `cs/useless-if-statement` if there is at least a comment.

csharp/ql/test/query-tests/Useless Code/FutileConditional/FutileConditional.cs

@@ -0,0 +1,34 @@
+using System;
+
+class FutileConditionalTest
+{
+
+    public void M(string s)
+    {
+        if (s.Length > 0) ; // $ Alert
+
+        if (s.Length > 1)
+        {
+        } // $ Alert
+
+        if (s.Length > 2) // GOOD: because of else-branch
+        {
+        }
+        else
+        {
+            Console.WriteLine("hello");
+        }
+
+        if (s.Length > 3)
+        {
+        }
+        else
+        {
+        } // $ Alert
+
+        if (s.Length > 4)
+        {
+            // GOOD: Because of the comment.
+        }
+    }
+}

csharp/ql/test/query-tests/Useless Code/FutileConditional/FutileConditional.expected

@@ -0,0 +1,3 @@
+| FutileConditional.cs:8:9:8:27 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
+| FutileConditional.cs:10:9:12:9 | if (...) ... | If-statement with an empty then-branch and no else-branch. |
+| FutileConditional.cs:22:9:27:9 | if (...) ... | If-statement with an empty then-branch and no else-branch. |

csharp/ql/test/query-tests/Useless Code/FutileConditional/FutileConditional.qlref

@@ -0,0 +1,2 @@
+query: Useless code/FutileConditional.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql

csharp/ql/test/query-tests/Useless Code/FutileConditional/options

@@ -0,0 +1,2 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj