[llvm] Fix file ignoring inside directories

[smeenai]

Summary

We have some ! patterns in the .gitignore (for the projects and runtimes
directories), and those patterns end up overriding the previous file
ignores, such that e.g. a .swp file inside the runtimes directory isn't
ignored. Move the file ignores last to ensure they take effect.

[jyknight]

I think we should instead remove the entire "tracked independently" parts, because that's no longer the recommended directory layout. And also remove these "global" ignores which you moved, because they're already in /.gitignore, and thus don't need to be in /llvm/.gitignore

[smeenai]

In D73253#1836910, @jyknight wrote:

I think we should instead remove the entire "tracked independently" parts, because that's no longer the recommended directory layout. And also remove these "global" ignores which you moved, because they're already in /.gitignore, and thus don't need to be in /llvm/.gitignore

I'm good doing so, although I'll note that we haven't officially removed support for the nested layout yet (although I can't imagine why someone would want to use the nested layout with the monorepo).

[compnerd]

I think that removing the nested layout is something which should be removed separately from this change. That would move us closer to declaring the nested layout as being unsupported. While I think that the move towards that makes sense, it should be brought up on llvm-dev first I think.

[mstorsjo]

In D73253#1837218, @smeenai wrote:

In D73253#1836910, @jyknight wrote:

I think we should instead remove the entire "tracked independently" parts, because that's no longer the recommended directory layout. And also remove these "global" ignores which you moved, because they're already in /.gitignore, and thus don't need to be in /llvm/.gitignore

I'm good doing so, although I'll note that we haven't officially removed support for the nested layout yet (although I can't imagine why someone would want to use the nested layout with the monorepo).

I still use the nested layout with the monorepo, due to interactions between cmake and ccache. For source files below the directory of the main toplevel cmake file (llvm-project/llvm), cmake will use relative paths if the build dir also is under the same directory (llvm-project/llvm/build). But for source files outside of that (llvm-project/clang), cmake will generate absolute paths.

In an asserts build, the pathname used to refer to a file ends up embedded in the built object files a lot (in each assert message). If the pathname is absolute, ccache is unable to share the built object files between two build trees on the same machine, and I quite intentionally use multiple build trees for being able to pre-build newer versions to populate ccache. In my setup, with the hw I have available for developing llvm, this is cruicial for not having to synchronously stop the main work for 1h+ every time I'd like to update to a newer master version.

If it's possible to build using a toplevel CMakeLists.txt directly in the llvm-project root, instead of in the llvm subdir, the proper monorepo build procedure would work fine for me. I brought this up on llvm-dev earlier, and @beanz said it would be doable but requires a bit of additional work: http://lists.llvm.org/pipermail/llvm-dev/2019-November/136466.html

So I'd prefer being able to symlink things into llvm/tools until this is resolved.

[smeenai]

I'll go ahead and land this as-is, given that the nested layout still has value, and we still need the duplication between the top-level .gitignore and llvm/.gitignore to correctly ignore files in the nested layout.

llvm/.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.
+# Nested build directory.
 #==============================================================================#
-# 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
-
-# Nested build directory
 /build
 
 #==============================================================================#
 # Explicit files to ignore (only matches one).
 #==============================================================================#
 # Various tag programs
 /tags
 /TAGS

 # clangd index
 .clangd
 
 #==============================================================================#
 # Files created in tree by the Go bindings.
 #==============================================================================#
 bindings/go/llvm/llvm_config.go
 bindings/go/llvm/workdir
+
+#==============================================================================#
+# File extensions to be ignored anywhere in the tree.
+# Placed at the end to override any previous ! patterns.
+#==============================================================================#
+# 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