From b56cbaa8465e74127f1ea216f813cd377295ad81 Mon Sep 17 00:00:00 2001
From: David Zbarsky <dzbarsky@gmail.com>
Date: Wed, 28 Jan 2026 12:10:02 -0500
Subject: [PATCH] Add runfiles crate

---
 rust/runfiles/Cargo.lock  |  7 +++++++
 rust/runfiles/Cargo.toml  | 10 ++++++++++
 rust/runfiles/runfiles.rs | 19 ++++++++++++++++++-
 3 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 rust/runfiles/Cargo.lock
 create mode 100644 rust/runfiles/Cargo.toml

diff --git a/rust/runfiles/Cargo.lock b/rust/runfiles/Cargo.lock
new file mode 100644
index 0000000000..3db66fb683
--- /dev/null
+++ b/rust/runfiles/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "runfiles"
+version = "0.1.0"
diff --git a/rust/runfiles/Cargo.toml b/rust/runfiles/Cargo.toml
new file mode 100644
index 0000000000..dde46286ab
--- /dev/null
+++ b/rust/runfiles/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "runfiles"
+version = "0.1.0"
+edition = "2018"
+license = "Apache-2.0"
+description = "Runfiles lookup library for Bazel-built Rust binaries and tests."
+repository = "https://github.com/bazelbuild/rules_rust"
+
+[lib]
+path = "runfiles.rs"
diff --git a/rust/runfiles/runfiles.rs b/rust/runfiles/runfiles.rs
index c2c4efb581..3dbcd79774 100644
--- a/rust/runfiles/runfiles.rs
+++ b/rust/runfiles/runfiles.rs
@@ -44,10 +44,27 @@ const TEST_SRCDIR_ENV_VAR: &str = "TEST_SRCDIR";
 #[macro_export]
 macro_rules! rlocation {
     ($r:expr, $path:expr) => {
-        $r.rlocation_from($path, env!("REPOSITORY_NAME"))
+        {
+            let repo = option_env!("REPOSITORY_NAME");
+            $r.rlocation_from($path, $crate::repository_name(repo))
+        }
     };
 }
 
+/// Return the build-time repository name.
+///
+/// Bazel sets the `REPOSITORY_NAME` environment variable while compiling this crate. When
+/// building via Cargo (e.g., from a git dependency), callers must either set the same
+/// environment variable at compile time or call `rlocation_from` directly with an explicit
+/// `source_repo`. This function panics if the value is not available.
+pub fn repository_name(repo: Option<&'static str>) -> &'static str {
+    repo.unwrap_or_else(|| {
+        panic!(
+            "REPOSITORY_NAME was not set at compile time; set it or call rlocation_from directly"
+        )
+    })
+}
+
 /// The error type for [Runfiles] construction.
 #[derive(Debug)]
 pub enum RunfilesError {