[clang] [clang][Diagnostics] Highlight code snippets (PR #66514)

[Aaron Ballman via cfe-commits]

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In-Reply-To: <llvm.org/llvm/llvm-project/pull/66514 at github.com>


AaronBallman wrote:

> @tbaederr I will need time to review/discuss this patch with other folks (@AaronBallman). I thought we had agreement on a direction before it got reverted completely and it is not clear to me that doing whole file lexing for each warning isn't going to negatively impact some folks.
> 
> But I haven't forgotten about it!

Re-lexing the file on each diagnostic works well enough for cases where there's only a few diagnostics in the file. But I do worry about the pathological case where there's a diagnostic on every line: that means compiling the file is O(N^2) in terms of lexing tokens whereas using checkpoints would still be O(N). Do you have an idea how bad the worst case performance looks compared to the best case? e.g., can you write a ~1MB test file that has no diagnostics and another similar ~1MB test file that has a warning diagnostic per line, and see what the performance difference is between runs of the compiler for those files?

https://github.com/llvm/llvm-project/pull/66514