Document and enforce that ignore-if cmds are run in CARGO_MANIFEST_DIR.

examples/rust_lang_tester/lang_tests/ignore2.rs

@@ -0,0 +1,8 @@
+// # Always ignore this test
+// ignore-if: cat examples/rust_lang_tester/lang_tests/ignore.rs
+// Compiler:
+//   status: success
+
+fn main() {
+    panic!("Shouldn't happen.");
+}

examples/rust_lang_tester/lang_tests/no_main.rs

@@ -3,6 +3,6 @@
 //   stderr:
 //     error[E0601]: `main` function not found in crate `no_main`
 //     ...
-//     error: aborting due to previous error
+//     error: aborting due to 1 previous error
 //
 //     For more information about this error, try `rustc --explain E0601`.

src/lib.rs

@@ -165,6 +165,7 @@
 //!
 //!   * `ignore-if: <cmd>` defines a shell command that will be run to determine whether to ignore
 //!     this test or not. If `<cmd>` returns 0 the test will be ignored, otherwise it will be run.
+//!     `<cmd>` will have its directory set to `CARGO_MANIFEST_DIR`.
 //!
 //! `lang_tester`'s output is deliberately similar to Rust's normal testing output. Running the
 //! example `rust_lang_tester` in this crate produces the following output:

src/tester.rs

@@ -659,6 +659,7 @@ fn test_file(
                     let ignore = if let Some(ignore_if) = tests.ignore_if {
                         Command::new(env::var("SHELL").unwrap_or_else(|_| "/bin/sh".to_owned()))
                             .args(["-c", &ignore_if])
+                            .current_dir(env::var("CARGO_MANIFEST_DIR").unwrap())
                             .stdin(process::Stdio::piped())
                             .stderr(process::Stdio::piped())
                             .stdout(process::Stdio::piped())