[LIT] Add a .gitignore to llvm/utils/lit

[EricWF]

Summary

This patch adds a .gitignore to the llvm/utils/lit folder. There are two main reasons why it would be useful if LIT had it's own gitignore.

1. When testing LIT in-tree, the tests create a folder test/Output which constantly has to be removed.
2. When using LIT in a standalone repo, outside of the LLVM tree (see https://github.com/delcypher/llvm-lit), .pyc files are not ignored because the LLVM .gitignore is not present.

I'm not sure what the policy is for .gitignore's in a subtree of LLVM, but if this is acceptable I would like to add it.

[EricWF]

@chandlerc: Do you have an objection to this patch on principle?

[chandlerc]

So, I don't think we should support testing in-tree because I don't like dirtying the tree.

What is the issue with .pyc files? I don't see how you get to that being a problem.

[jroelofs]

If you don't want *.pyc files, why not set the PYTHONDONTWRITEBYTECODE env var, or sys.dont_write_bytecode = false, or use python -B?

[EricWF]

In D11330#208648, @chandlerc wrote:

So, I don't think we should support testing in-tree because I don't like dirtying the tree.

"testing in-tree" is probably the wrong way to describe it. Currently LIT doesn't generate a check-lit rule
or a lit.site.cfg file. The only way (that I know of) to test LIT is to run lit.py llvm-src/utils/lit/tests. Because this doesn't
set the config.test_exec_root option the ShTest temporary directory will be llvm-src/utils/lit/tests/Output.

One way to keep the tree clean would be to set config.test_exec_root to a created temporary directory. However
I don't think this directory can be cleaned up though (other than by the OS).

In D11330#208648, @chandlerc wrote:

What is the issue with .pyc files? I don't see how you get to that being a problem.

This is a problem I have outside of my LLVM work (so it's not a real reason to make this change). I use LIT on other projects as a git submodule. The LIT submodule is just llvm/utils/lit so llvm/.gitignore is not present. When python ends up generating the llvm/utils/lit/lit/*.pyc files they are not ignored by version control.

In D11330#208658, @jroelofs wrote:

If you don't want *.pyc files, why not set the PYTHONDONTWRITEBYTECODE env var, or sys.dont_write_bytecode = false, or use python -B?

I don't mind the *.pyc files, I just want version control to ignore them when I'm using LIT as a submodule.

[chandlerc]

In D11330#208733, @EricWF wrote:

In D11330#208648, @chandlerc wrote:

So, I don't think we should support testing in-tree because I don't like dirtying the tree.

"testing in-tree" is probably the wrong way to describe it. Currently LIT doesn't generate a check-lit rule
or a lit.site.cfg file. The only way (that I know of) to test LIT is to run lit.py llvm-src/utils/lit/tests. Because this doesn't
set the config.test_exec_root option the ShTest temporary directory will be llvm-src/utils/lit/tests/Output.

One way to keep the tree clean would be to set config.test_exec_root to a created temporary directory. However
I don't think this directory can be cleaned up though (other than by the OS).

Doing this or finding some other way of testing lit without dirtying the source tree sounds like the better fix to me.

In D11330#208648, @chandlerc wrote:

What is the issue with .pyc files? I don't see how you get to that being a problem.

This is a problem I have outside of my LLVM work (so it's not a real reason to make this change). I use LIT on other projects as a git submodule. The LIT submodule is just llvm/utils/lit so llvm/.gitignore is not present. When python ends up generating the llvm/utils/lit/lit/*.pyc files they are not ignored by version control.

Well, you're dropping your submodule into some other tree, use its .gitignore? I guess that doesn't work because of how submodules work? You can create a clone-local ignores file, maybe use that?

Anyways, I don't think we should work around this in LLVM.

We could graduate lit to a full project and that would fix this. But I don't really think we should do that either, because I think it is useful for lit to remain crazy simple and *only* serve the purposes that LLVM testing has for it, and not become a fully generic test runner.

My 2 cents, others might disagree.

In D11330#208658, @jroelofs wrote:

If you don't want *.pyc files, why not set the PYTHONDONTWRITEBYTECODE env var, or sys.dont_write_bytecode = false, or use python -B?

I don't mind the *.pyc files, I just want version control to ignore them when I'm using LIT as a submodule.

[EricWF]

Abandoning due to @chandlerc's feedback. I'm going to fix the Output problem differently.

utils/lit/.gitignore

+#==============================================================================#
+# This file specifies intentionally untracked files that git should ignore.
+# See: http://www.kernel.org/pub/software/scm/git/docs/gitignore.html
+#
+# This file is intentionally different from the output of `git svn show-ignore`,
+# as most of those are useless.
+#==============================================================================#
+
+#==============================================================================#
+# File extensions to be ignored anywhere in the tree.
+#==============================================================================#
+# Temp files created by most text editors.
+*~
+# Merge files created by git.
+*.orig
+# Byte compiled python modules.
+*.pyc
+# vim swap files
+.*.sw?
+.sw?
+#OS X specific files.
+.DS_store
+
+#==============================================================================#
+# Explicit files to ignore (only matches one).
+#==============================================================================#
+# Output folder created while testing lit
+/test/Output