Add BUILD_VERSION to lib.rs

In CMake this used a `version` file in the CARGO_MANIFEST_DIR, but
relying on that is problematic due to change-detection, as if we add
`cargo-rerun-if-changed:version`, cargo would rerun every time if the file does
not exist, since cargo would expect the file to be generated by the
build-script. We could generate it, but that relies on the output of `git
describe`, whose dependencies we can only limit to anything in the
`.git`-folder, again causing unnecessary build-script runs.

Instead, this reads the `FISH_BUILD_VERSION`-env-variable at compile time
instead of the `version`-file, and falls back to calling git-describe through
the `git_version`-proc-macro. We thus do not need to deal with extraneous
build-script running.

Cargo.lock

@@ -337,6 +337,7 @@ dependencies = [
  "cxx-gen",
  "errno 0.2.8",
  "fast-float",
+ "git-version",
  "hexponent",
  "inventory",
  "lazy_static",
@@ -368,6 +369,28 @@ dependencies = [
  "wasi",
 ]
 
+[[package]]
+name = "git-version"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6b0decc02f4636b9ccad390dcbe77b722a77efedfa393caf8379a51d5c61899"
+dependencies = [
+ "git-version-macro",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "git-version-macro"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fe69f1cbdb6e28af2bac214e943b99ce8a0a06b447d15d3e61161b0423139f3f"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "glob"
 version = "0.3.1"
@@ -705,6 +728,12 @@ dependencies = [
  "version_check",
 ]
 
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.20+deprecated"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc375e1527247fe1a97d8b7156678dfe7c1af2fc075c9a4db3690ecd2a148068"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.66"

Cargo.toml

@@ -60,6 +60,7 @@ rand = { version = "0.8.5", features = ["small_rng"] }
 unixstring = "0.2.7"
 widestring = "1.0.2"
 rand_pcg = "0.3.1"
+git-version = "0.3"
 
 [build-dependencies]
 autocxx-build = "0.23.1"
@@ -80,4 +81,4 @@ fish-ffi-tests = ["inventory"]
 
 # The following features are auto-detected by the build-script and should not be enabled manually.
 asan = []
-bsd = []
+bsd = []

fish-rust/build.rs

@@ -14,7 +14,7 @@ fn main() {
         .file("fish-rust/src/compat.c")
         .compile("libcompat.a");
 
-    let rust_dir = std::env::var("CARGO_MANIFEST_DIR").expect("Env var CARGO_MANIFEST_DIR missing");
+    let rust_dir = env!("CARGO_MANIFEST_DIR");
     let target_dir =
         std::env::var("FISH_RUST_TARGET_DIR").unwrap_or(format!("{}/{}", rust_dir, "target/"));
     let cpp_fish_src_dir = format!("{}/{}", rust_dir, "src/");

fish-rust/src/lib.rs

@@ -10,6 +10,11 @@
 #![allow(clippy::ptr_arg)]
 #![allow(clippy::field_reassign_with_default)]
 
+pub const BUILD_VERSION: &str = match option_env!("FISH_BUILD_VERSION") {
+    Some(v) => v,
+    None => git_version::git_version!(args = ["--always", "--dirty=-dirty"], fallback = "unknown"),
+};
+
 #[macro_use]
 mod common;