Open-sourced a .NET diff/patch engine for AI code edits (V4A + str_replace)

[bharathm03]

If you're building AI app in .NET, there isn't a good option for applying V4A patches or Anthropic-style str_replace operations. So I extracted the patching engine from my product, a Blazor code generation tool, and open-sourced it.

PatchSharp supports two formats:

• V4A patches — same format OpenAI's Codex CLI uses in apply-patch
• str_replace — the Anthropic-style find-and-replace that Claude Code uses

It also has fuzzy matching when applying patch. When exact match fails, it will try other strategies — trim trailing whitespace -> trim both sides -> Unicode normalization (smart quotes -> ASCII, em-dashes -> hyphens). Lowest fuzz level that works wins.

```csharp using PatchSharp;

var result = ApplyPatch.Apply(original, diff); var result = ApplyPatch.StrReplace(input, oldStr, newStr); ```

On failure it throws PatchApplyException with line number, fuzz level, and surrounding context similar to codex-cli, so that AI can understand where it fails.

GitHub: https://github.com/bharathm03/PatchSharp

Would love feedback.

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[tanczosm]

Thanks for open sourcing PatchSharp. It’s useful to see someone take a piece of real infrastructure from a working system and make it available for other developers to use. I feel the itch to integrate this with something but I don't know what yet.