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

[Timm Baeder via cfe-commits]

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


tbaederr wrote:

So, I have a test file of about 4.5MB where every line is a `#warning`. Not sure how I should create a "similar" file without diagnostics though.

```
# ls -lah test.cpp
-rw-r--r--. 1 root root 4.5M Dec 12 02:52 test.cpp
# wc -l test.cpp
357391 test.cpp
```

With a release build, the time is:
```
# time bin/clang++ -cc1 ./test.cpp > out.txt 2>&1
real    1m3.967s
user    0m52.142s
sys     0m11.606s
```
this is  _without_ any highlighting, since the file is too big.

Here's the same file with highlighting:
```
# time bin/clang++ -cc1 ./test.cpp -fmax-highlight-file-size=5242880 > out.txt 2>&1
real    72m28.551s
user    72m11.610s
sys     0m11.561s
```

(not that we definitely shouldn't take any longer here, since we don't emit any highlighting anyway because we're piping into a file. Need to fix that).

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