Port wiki pages which I created in the cquery repo

Debugging.md

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+First of all, use a `--variant=debug` [[Build]]. It is compiled with `-O0 -g` while the default `--variant=release` is `-O3 -g`.
+
+### Logs
+
+`--log-file=/tmp/cq.log`
+
+### Dump LSP requests/responses
+
+`--record=/tmp/ccls`: You can find stdin/stdout (LSP requests/responses) in `/tmp/cquery.{in,out}`
+
+Alternatively, enable logs and pass the `--log-all-to-stderr` option to the ccls executable (`bin/cquery --log-file=/tmp/cq.log --log-all-to-stderr`). You can find stderr output in:
+
+* LanguageClient-neovim: `/tmp/LanguageServer.log` (default)
+* Emacs lsp-mode: `*lsp-ccls stderr*` buffer. They will also go to `*message*` buffer if `(setq lsp-print-io t)`
+* VSCode: TODO
+
+You can also use sysdig on Linux:
+```zsh
+sudo sysdig -As999 --unbuffered -p '%evt.type %proc.name %evt.buffer' "proc.exe contains ccls and fd.type=pipe" | egrep -v '^Content|^$'
+```
+
+### Stopping at the start to debug early issues
+
+To debug individual LSP requests, you can attach your debugger after ccls has done indexing. However,
+for many other issues, such as project file loading (`project.cc`) and C/C++ parsing and indexing `clang_indexer.cc`, you need to set an early breakpoint to be able to trace the code.
+
+It is recommended to use [[LanguageClient-neovim|Neovim]] for debugging (even if you use Emacs or VSCode) because it can be started with simple shell command.
+
+```vim
+# vimrc
+nn ,al :LanguageClientStart<cr>
+```
+
+```zsh
+rm -r /tmp/ccls && CQUERY_TRACEME=1 nvim a.cc +'normal ,al'
+```
+
+The Neovim buffer will hang there because `CCLS_TRACEME=1` causes the bin/cquery process to SIGTSTP itself. In another shell, `gdb -p $(pgrep -fn bin/cquery)`
+
+### Poor man's breakpoint
+
+Insert an infinite loop `volatile static int z=0;while(!z);` somewhere and ccls will stop there. Attach to the cquery process with `gdb -p $(pgrep -fn cquery)`. Set some breakpoints, use `print` commands, and execute `p z=1` for continuing. 
+
+When setting breakpoints, if several threads may stop on the same breakpoint (e.g. concurrent indexer threads),
+execute `set scheduler-locking on`.
+
+### Using a debugger
+
+Cache files are deleted to avoid possible issues related to stale cache. `CCLS_TRACEME=1` causes the cquery process to stop at the start of `main()`. You may attach to the process with:
+
+* `gdb -p $(pgrep -fn ccls)`. Invoke `signal SIGCONT` if you want cquery to continue running after detaching of gdb.
+* `lldb -p $(pgrep -fn ccls)`. Invoke `pro sig SIGCONT` when the process resumes (with a `c` command) if you want cquery to continue running after detaching.
+
+### libclang or indexer callback issues
+
+`export LIBCLANG_DISABLE_CRASH_RECOVERY=1` disables libclang crash recovery. In case of libclang or indexer callback issues, you will not see `libclang: crash detected` in the log file but get a process crash. And if you attach a debugger before it crashes, you can get the stack trace.
+
+
+## Developing
+
+### Diagnose whether requests are handled correctly
+
+Set breakpoints in `src/messages/*` files. They are inbound message handlers.