fix(build): guide users when zig is missing (#2281)

build.rs now reports how to install Zig 0.15.2 (brew install zig@0.15
on macOS, ziglang.org elsewhere) and mentions the ZIG environment
variable instead of panicking with a bare NotFound error.

Co-authored-by: JJ Liebig <jonathan.liebig@gmail.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/build.rs b/build.rs
index b7a6a005..7a2ac11f 100644
--- a/build.rs
+++ b/build.rs
@@ -61,7 +61,7 @@ fn main() {
         .to_string();
 
     let zig = env::var("ZIG").unwrap_or_else(|_| "zig".into());
-    let mut command = Command::new(zig);
+    let mut command = Command::new(&zig);
     command
         .arg("build")
         .arg("-Demit-lib-vt")
@@ -77,7 +77,18 @@ fn main() {
     let status = command
         .current_dir(&vendored_dir)
         .status()
-        .expect("failed to execute zig build for vendored libghostty-vt");
+        .unwrap_or_else(|err| {
+            if err.kind() == std::io::ErrorKind::NotFound {
+                panic!(
+                    "zig executable not found (looked for {zig:?}; set the ZIG \
+                     environment variable to point at the zig binary). Building \
+                     the vendored libghostty-vt requires Zig 0.15.2: on macOS run \
+                     `brew install zig@0.15`, elsewhere install it from \
+                     https://ziglang.org/download/, then retry the build"
+                );
+            }
+            panic!("failed to execute zig build for vendored libghostty-vt: {err}");
+        });
     assert!(
         status.success(),
         "zig build for vendored libghostty-vt failed: {status}"