rust/compiler/rustc_codegen_gcc/doc/subtree.md

git subtree sync

rustc_codegen_gcc is a subtree of the rust compiler. As such, it needs to be sync from time to time to ensure changes that happened on their side are also included on our side.

How to install a forked git-subtree

Using git-subtree with rustc requires a patched git to make it work. The PR that is needed is here. Use the following instructions to install it:

git clone git@github.com:tqc/git.git
cd git
git checkout tqc/subtree
make
make install
cd contrib/subtree
make
cp git-subtree ~/bin

Syncing with rust compiler

Do a sync with this command:

PATH="$HOME/bin:$PATH" ~/bin/git-subtree push -P compiler/rustc_codegen_gcc/ ../rustc_codegen_gcc/ sync_branch_name
cd ../rustc_codegen_gcc
git checkout master
git pull
git checkout sync_branch_name
git merge master

To send the changes to the rust repo:

cd ../rust
git pull origin master
git checkout -b subtree-update_cg_gcc_YYYY-MM-DD
PATH="$HOME/bin:$PATH" ~/bin/git-subtree pull --prefix=compiler/rustc_codegen_gcc/ https://github.com/rust-lang/rustc_codegen_gcc.git master
git push

# Immediately merge the merge commit into cg_gcc to prevent merge conflicts when syncing from rust-lang/rust later.
PATH="$HOME/bin:$PATH" ~/bin/git-subtree push -P compiler/rustc_codegen_gcc/ ../rustc_codegen_gcc/ sync_branch_name

TODO: write a script that does the above.

https://rust-lang.zulipchat.com/#narrow/stream/301329-t-devtools/topic/subtree.20madness/near/258877725