Git DEFMT_VERSION doesn't get updated when doing a Git commit.

[Dirbaio]

• In a firmware project, add a [patch.crates-io] pointing to a local checkout of the defmt repo
• Modify some defmt .rs files
• Build the firmware, it gets DEFMT_VERSION = <commit 1>.
• The firmware runs great with the modified defmt, you decide to do a defmt commit to prepare a juicy PR
• do git commit in the defmt repo
• Now defmt HEAD is <commit 2>
• Build the firmware, it STILL gets DEFMT_VERSION = <commit 1> because build.rs doesn't re-run because you didn't edit any .rs files since last build.

[japaric]

This git mechanism is meant to be used with git dependencies.

In a firmware project, add a [patch.crates-io] pointing to a local checkout of the defmt repo

is the override a path dependency or a git dependency? it should be a git dependency

[patch.crates-io]
defmt = { git = "file:///home/japaric/rust/defmt", branch = "wip-branch" }
#                ^^^^ git dependency that lives in the local file system

with a git dependency after you do a defmt commit you need to run cargo update from the firmware folder to make the lock file use the newer commit

---

the problem with path dependencies is that:

1. git commits are not recognized by Cargo as changes so, afaik, there's no way to re-run build.rs on a new commit. the work around is to make the build script always run by doing touch build.rs from it but this causes crates to be re-built every time you do cargo build (even if nothing changed)

2. you can build a crate that has uncommited changes; these changes won't be included in the DEFMT_VERSION string -- the string will still report the last commit hash. there are some workarounds for this: you can include a hash of git status in DEFMT_VERSION but not sure if that's too reliable because of (1).

[jonas-schievink]

1. git commits are not recognized by Cargo as changes so, afaik, there's no way to re-run build.rs on a new commit.

Super hacky idea, but would it work to emit rerun-if-changed directives for .git/HEAD and whatever file HEAD points to? Not terribly familiar with git, but I think that should cover new commits?