Fix discard handling for newer Assert.Throws codefix (#5117)

microsoft · Feb 24, 2025 · b3a19f7 · b3a19f7
1 parent 149076d
commit b3a19f7
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Showing 2 changed files with 93 additions and 7 deletions.
diff --git a/src/Analyzers/MSTest.Analyzers.CodeFixes/UseNewerAssertThrowsFixer.cs b/src/Analyzers/MSTest.Analyzers.CodeFixes/UseNewerAssertThrowsFixer.cs
@@ -100,7 +100,7 @@ private static SyntaxNode UpdateMethodName(SyntaxEditor editor, InvocationExpres
             {
                 editor.ReplaceNode(
                     lambdaSyntax.ExpressionBody,
-                    AssignToDiscard(lambdaSyntax.ExpressionBody));
+                    AssignToDiscardIfNeeded(lambdaSyntax.ExpressionBody));
             }
             else if (lambdaSyntax.Block is not null)
             {
@@ -126,7 +126,7 @@ private static SyntaxNode UpdateMethodName(SyntaxEditor editor, InvocationExpres
                         continue;
                     }
 
-                    ExpressionStatementSyntax returnReplacement = SyntaxFactory.ExpressionStatement(AssignToDiscard(returnStatement.Expression));
+                    ExpressionStatementSyntax returnReplacement = SyntaxFactory.ExpressionStatement(AssignToDiscardIfNeeded(returnStatement.Expression));
 
                     if (returnStatement.Parent is BlockSyntax blockSyntax)
                     {
@@ -151,12 +151,24 @@ private static SyntaxNode UpdateMethodName(SyntaxEditor editor, InvocationExpres
                 SyntaxFactory.ParenthesizedLambdaExpression(
                     SyntaxFactory.ParameterList(),
                     block: null,
-                    expressionBody: AssignToDiscard(SyntaxFactory.InvocationExpression(SyntaxFactory.ParenthesizedExpression(expressionSyntax).WithAdditionalAnnotations(Simplifier.Annotation)))));
+                    expressionBody: SyntaxFactory.InvocationExpression(SyntaxFactory.ParenthesizedExpression(expressionSyntax).WithAdditionalAnnotations(Simplifier.Annotation))));
         }
 
         return editor.GetChangedRoot();
     }
 
-    private static AssignmentExpressionSyntax AssignToDiscard(ExpressionSyntax expression)
-        => SyntaxFactory.AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, SyntaxFactory.IdentifierName("_"), expression);
+    private static ExpressionSyntax AssignToDiscardIfNeeded(ExpressionSyntax expression)
+        => NeedsDiscard(expression)
+            ? SyntaxFactory.AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, SyntaxFactory.IdentifierName("_"), expression)
+            : expression;
+
+    private static bool NeedsDiscard(ExpressionSyntax expression)
+        => expression is not InvocationExpressionSyntax &&
+            expression is not AssignmentExpressionSyntax &&
+            !expression.IsKind(SyntaxKind.PostIncrementExpression) &&
+            !expression.IsKind(SyntaxKind.PostDecrementExpression) &&
+            !expression.IsKind(SyntaxKind.PreIncrementExpression) &&
+            !expression.IsKind(SyntaxKind.PreDecrementExpression) &&
+            expression is not AwaitExpressionSyntax &&
+            expression is not ObjectCreationExpressionSyntax;
 }
diff --git a/test/UnitTests/MSTest.Analyzers.UnitTests/UseNewerAssertThrowsAnalyzerTests.cs b/test/UnitTests/MSTest.Analyzers.UnitTests/UseNewerAssertThrowsAnalyzerTests.cs
@@ -250,7 +250,7 @@ public class MyTestClass
                 public void MyTestMethod()
                 {
                     Func<object> action = () => _ = 5;
-                    Assert.ThrowsExactly<Exception>(() => _ = action());
+                    Assert.ThrowsExactly<Exception>(() => action());
                 }
             }
             """;
@@ -288,11 +288,85 @@ public class MyTestClass
                 public void MyTestMethod()
                 {
                     Func<object> action = () => _ = 5;
-                    Assert.ThrowsExactly<Exception>(() => _ = (action + action)());
+                    Assert.ThrowsExactly<Exception>(() => (action + action)());
                 }
             }
             """;
 
         await VerifyCS.VerifyCodeFixAsync(code, fixedCode);
     }
+
+    [TestMethod]
+    public async Task VariousTestCasesForDiscard()
+    {
+        string code = """
+            using System;
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+            [TestClass]
+            public sealed class Test1
+            {
+                [TestMethod]
+                public void TestMethod1()
+                {
+                    int[] numbers = [1];
+                    int x = 0;
+                    string s = "";
+
+                    [|Assert.ThrowsException<ArgumentException>(() => VoidMethod(1))|];
+                    [|Assert.ThrowsException<ArgumentException>(() => NonVoidMethod(1))|];
+                    [|Assert.ThrowsException<ArgumentException>(() => _ = NonVoidMethod(1))|];
+                    [|Assert.ThrowsException<ArgumentException>(() => new Test1())|];
+                    [|Assert.ThrowsException<ArgumentException>(() => _ = new Test1())|];
+                    [|Assert.ThrowsException<ArgumentException>(() => numbers[0] = 4)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => x++)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => x--)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => ++x)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => --x)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => s!)|];
+                    [|Assert.ThrowsException<ArgumentException>(() => !true)|];
+                }
+
+                private void VoidMethod(object o) => _ = o;
+
+                private int NonVoidMethod(int i) => i;
+            }
+            """;
+
+        string fixedCode = """
+            using System;
+            using Microsoft.VisualStudio.TestTools.UnitTesting;
+            
+            [TestClass]
+            public sealed class Test1
+            {
+                [TestMethod]
+                public void TestMethod1()
+                {
+                    int[] numbers = [1];
+                    int x = 0;
+                    string s = "";
+
+                    Assert.ThrowsExactly<ArgumentException>(() => VoidMethod(1));
+                    Assert.ThrowsExactly<ArgumentException>(() => NonVoidMethod(1));
+                    Assert.ThrowsExactly<ArgumentException>(() => _ = NonVoidMethod(1));
+                    Assert.ThrowsExactly<ArgumentException>(() => new Test1());
+                    Assert.ThrowsExactly<ArgumentException>(() => _ = new Test1());
+                    Assert.ThrowsExactly<ArgumentException>(() => numbers[0] = 4);
+                    Assert.ThrowsExactly<ArgumentException>(() => x++);
+                    Assert.ThrowsExactly<ArgumentException>(() => x--);
+                    Assert.ThrowsExactly<ArgumentException>(() => ++x);
+                    Assert.ThrowsExactly<ArgumentException>(() => --x);
+                    Assert.ThrowsExactly<ArgumentException>(() => _ = s!);
+                    Assert.ThrowsExactly<ArgumentException>(() => _ = !true);
+                }
+            
+                private void VoidMethod(object o) => _ = o;
+            
+                private int NonVoidMethod(int i) => i;
+            }
+            """;
+
+        await VerifyCS.VerifyCodeFixAsync(code, fixedCode);
+    }
 }