Fixed LoggerMessageGenerator message escaping.

[John-Leitch]

This PR addresses bug #123786 by escaping all non-printable characters (< 0x20) in the emitted message. \r and \n are emitted using the same escape sequence, while other non-printable characters are emitted as hex escape sequences e.g. \x00. Escaping of \ is also addressed. Finally, an additional test was added to cover these behaviors.

[Copilot]

Pull request overview

Fixes LoggerMessageGenerator emitting malformed C# string literals by escaping backslashes and all non-printable characters (< 0x20) when generating source, and adds a regression test covering these escaping scenarios.

Changes:

• Update the emitter to escape \ and all control characters (< 0x20) using \xNN (while keeping \r/\n as named escapes).
• Add a new theory test validating the generated source is syntactically valid and contains the expected escaped message literal.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.Emitter.cs	Extends message escaping to include backslashes and all control characters so generated string literals remain well-formed.
src/libraries/Microsoft.Extensions.Logging.Abstractions/tests/Microsoft.Extensions.Logging.Generators.Tests/LoggerMessageGeneratorEmitterTests.cs	Adds a theory-based regression test for message escaping (backslash, quotes, CR/LF, and \xNN escapes).

[tarekgh]

    private static string ConvertEndOfLineAndQuotationCharactersToEscapeForm(string s)

We should get rid of this method and just call SymbolDisplay.FormatLiteral. Here is example of how the extension source gen does it https://github.com/dotnet/extensions/blob/140e4055f7b12d4cf29ec63924c88520ccfc6064/src/Generators/Microsoft.Gen.Logging/Emission/Emitter.Utils.cs#L16

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Refers to: src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.Emitter.cs:580 in 2f6a0f4. [](commit_id = 2f6a0f4, deletion_comment = False)

[John-Leitch]

@tarekgh, pushed your suggested changes and added some additional test coverage.

[tarekgh]

Thanks @John-Leitch. I pushed a small test fix, LGTM otherwise.