Reject carriage returns in verified files instead of normalizing

The text comparison previously read the verified file via
ReadStringBuilderWithFixedLines, silently converting \r\n and \r to \n.
Now it reads the file directly and throws if it contains a \r, linking
to the text-file-settings docs. Verified files are LF-only (enforced by
.gitattributes), so this surfaces misconfigured line endings rather than
masking them.

Drop the now-unused ReadStringBuilderWithFixedLines(string) overload and
rewrite the two net9 NewLineTests to assert the throw.

Author: SimonCropp

src/Verify.Tests/NewLineTests.cs

@@ -44,35 +44,27 @@ public async Task StringWithDifferingNewline()
     {
         var fullPath = CurrentFile.Relative("NewLineTests.StringWithDifferingNewline.verified.txt");
         File.Delete(fullPath);
+        var settings = new VerifySettings();
+        settings.DisableRequireUniquePrefix();
+
+        // A verified file containing \r is rejected rather than silently normalized
         await File.WriteAllTextAsync(fullPath, "a\r\nb");
-        await Verify("a\r\nb");
-        PrefixUnique.Clear();
-        await Verify("a\rb");
-        PrefixUnique.Clear();
-        await Verify("a\nb");
-        PrefixUnique.Clear();
+        var crlf = await Assert.ThrowsAnyAsync<Exception>(() => Verify("a\nb", settings));
+        Assert.Contains("carriage return", crlf.ToString());
 
-        File.Delete(fullPath);
+        await File.WriteAllTextAsync(fullPath, "a\rb");
+        var cr = await Assert.ThrowsAnyAsync<Exception>(() => Verify("a\nb", settings));
+        Assert.Contains("carriage return", cr.ToString());
+
+        // A verified file using \n still matches received content normalized to \n
         await File.WriteAllTextAsync(fullPath, "a\nb");
-        await Verify("a\r\nb");
-        PrefixUnique.Clear();
-        await Verify("a\rb");
-        PrefixUnique.Clear();
-        await Verify("a\nb");
-        PrefixUnique.Clear();
+        await Verify("a\r\nb", settings);
+        await Verify("a\rb", settings);
+        await Verify("a\nb", settings);
 
         File.Delete(fullPath);
-        await File.WriteAllTextAsync(fullPath, "a\rb");
-        await Verify("a\r\nb");
-        PrefixUnique.Clear();
-        await Verify("a\rb");
-        PrefixUnique.Clear();
-        await Verify("a\nb");
-        File.Delete(fullPath);
     }
 
-#if NET9_0
-
     [Fact]
     public async Task TrailingNewlinesRaw()
     {
@@ -81,16 +73,12 @@ public async Task TrailingNewlinesRaw()
         var settings = new VerifySettings();
         settings.DisableRequireUniquePrefix();
 
+        // A verified file containing \r is rejected
         await File.WriteAllTextAsync(file, "a\r\n");
-        await Verify("a\r\n", settings);
-        await Verify("a\n", settings);
-        await Verify("a", settings);
-
-        await File.WriteAllTextAsync(file, "a\r\n\r\n");
-        await Verify("a\r\n\r\n", settings);
-        await Verify("a\n\n", settings);
-        await Verify("a\n", settings);
+        var exception = await Assert.ThrowsAnyAsync<Exception>(() => Verify("a\n", settings));
+        Assert.Contains("carriage return", exception.ToString());
 
+        // Trailing \n tolerance still applies for \n-only verified files
         await File.WriteAllTextAsync(file, "a\n");
         await Verify("a\n", settings);
         await Verify("a", settings);
@@ -100,7 +88,6 @@ public async Task TrailingNewlinesRaw()
         await Verify("a\n", settings);
         File.Delete(file);
     }
-#endif
 
     //TODO: add test for trailing newlines
     // [Fact]

src/Verify/Compare/Comparer.cs

@@ -9,7 +9,13 @@ public static async Task<EqualityResult> Text(FilePair filePair, StringBuilder r
             return new(Equality.New, null, received, null);
         }
 
-        var verified = await IoHelpers.ReadStringBuilderWithFixedLines(filePair.VerifiedPath);
+        var verifiedText = await File.ReadAllTextAsync(filePair.VerifiedPath);
+        if (verifiedText.Contains('\r'))
+        {
+            throw new($@"Verified file must use \n line endings, but it contains a \r (carriage return). Path: {filePair.VerifiedPath}. See https://github.com/verifytests/verify#text-file-settings");
+        }
+
+        var verified = new StringBuilder(verifiedText);
         var result = await CompareStrings(filePair.Extension, received, verified, settings, bypassComparer);
         if (result.IsEqual)
         {
@@ -52,4 +58,4 @@ static Task<CompareResult> CompareStrings(string extension, StringBuilder receiv
 
         return Task.FromResult(new CompareResult(isEqual));
     }
-}
+}

src/Verify/IoHelpers.cs

@@ -208,12 +208,6 @@ internal static string ResolveDirectoryFromSourceFile(string sourceFile)
         throw new($"Unable to resolve directory. sourceFile: {sourceFile}");
     }
 
-    public static async Task<StringBuilder> ReadStringBuilderWithFixedLines(string path)
-    {
-        using var stream = OpenRead(path);
-        return await stream.ReadStringBuilderWithFixedLines();
-    }
-
     public static async Task WriteStream(string path, Stream stream)
     {
         Directory.CreateDirectory(Path.GetDirectoryName(path)!);