SA1313 codefix will remove underscore if necessary

Author: vweijsters

StyleCop.Analyzers/StyleCop.Analyzers.Test/NamingRules/SA1312UnitTests.cs

@@ -148,12 +148,19 @@ public void MethodName()
     }
 }";
 
+            var fixedTestCode = @"public class TypeName
+{
+    public void MethodName()
+    {
+        string bar = ""baz"";
+    }
+}";
+
             DiagnosticResult expected = this.CSharpDiagnostic().WithArguments("_bar").WithLocation(5, 16);
 
             await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
-
-            // Verify the code fix doesn't do anything in this case
-            await this.VerifyCSharpFixAsync(testCode, testCode).ConfigureAwait(false);
+            await this.VerifyCSharpDiagnosticAsync(fixedTestCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpFixAsync(testCode, fixedTestCode).ConfigureAwait(false);
         }
 
         [Fact]

StyleCop.Analyzers/StyleCop.Analyzers.Test/NamingRules/SA1313UnitTests.cs

@@ -114,25 +114,6 @@ public void MethodName(string bar, string car, string par)
             await this.VerifyCSharpFixAsync(testCode, fixedCode).ConfigureAwait(false);
         }
 
-        [Fact]
-        public async Task TestParameterStartingWithAnUnderscoreAsync()
-        {
-            // Makes sure SA1313 is reported for parameters starting with an underscore
-            var testCode = @"public class TypeName
-{
-    public void MethodName(string _bar)
-    {
-    }
-}";
-
-            DiagnosticResult expected = this.CSharpDiagnostic().WithArguments("_bar").WithLocation(3, 35);
-
-            await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
-
-            // Verify the code fix doesn't do anything in this case
-            await this.VerifyCSharpFixAsync(testCode, testCode).ConfigureAwait(false);
-        }
-
         [Fact]
         public async Task TestParameterStartingWithLetterAsync()
         {
@@ -505,6 +486,48 @@ public interface IDerivedTest : ITest, IEmptyInterface
             await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
         }
 
+        /// <summary>
+        /// This is a regression test for DotNetAnalyzers/StyleCopAnalyzers#1604:
+        /// https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/1604
+        /// </summary>
+        /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
+        [Fact]
+        public async Task TestCodeFixProperlyRemovesUnderscoreAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public TestClass(string _text)
+        : this(_text, false)
+    {
+    }
+
+    public TestClass(string text, bool flag)
+    {
+    }
+}
+";
+
+            var fixedCode = @"
+public class TestClass
+{
+    public TestClass(string text)
+        : this(text, false)
+    {
+    }
+
+    public TestClass(string text, bool flag)
+    {
+    }
+}
+";
+
+            var expected = this.CSharpDiagnostic().WithLocation(4, 29).WithArguments("_text");
+            await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpDiagnosticAsync(fixedCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpFixAsync(testCode, fixedCode).ConfigureAwait(false);
+        }
+
         protected override IEnumerable<DiagnosticAnalyzer> GetCSharpDiagnosticAnalyzers()
         {
             yield return new SA1313ParameterNamesMustBeginWithLowerCaseLetter();

StyleCop.Analyzers/StyleCop.Analyzers/NamingRules/RenameToLowerCaseCodeFixProvider.cs

@@ -45,15 +45,11 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
             foreach (var diagnostic in context.Diagnostics)
             {
-                if (!this.FixableDiagnosticIds.Contains(diagnostic.Id))
-                {
-                    continue;
-                }
-
                 var token = root.FindToken(diagnostic.Location.SourceSpan.Start);
                 if (!string.IsNullOrEmpty(token.ValueText))
                 {
-                    var newName = char.ToLower(token.ValueText[0]) + token.ValueText.Substring(1);
+                    var newName = token.ValueText.TrimStart('_');
+                    newName = char.ToLower(newName[0]) + newName.Substring(1);
                     context.RegisterCodeFix(CodeAction.Create(string.Format(NamingResources.RenameToCodeFix, newName), cancellationToken => RenameHelper.RenameSymbolAsync(document, root, token, newName, cancellationToken), equivalenceKey: nameof(RenameToLowerCaseCodeFixProvider)), diagnostic);
                 }
             }