rust: detect user-specified custom targets in compiletest

Fixes: thread 'main' panicked at 'failed to gather the target spec
       for '<arch>-unknown-linux-gnu', synthetic_targets.rs:66:9

Detect and fetch custom target configurations when rustc is
bootstrapped in rust oe-selftest.

(From OE-Core rev: fdd9385d9845d628e10179598fc42d29519c5dfd)

Signed-off-by: Yash Shinde <Yash.Shinde@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 90 insertions, 0 deletions

diff --git a/meta/recipes-devtools/rust/files/custom-target-cfg.patch b/meta/recipes-devtools/rust/files/custom-target-cfg.patch
new file mode 100644
index 0000000000..15a7f252cc
--- /dev/null
+++ b/meta/recipes-devtools/rust/files/custom-target-cfg.patch
@@ -0,0 +1,90 @@
+Detect and fetch custom target configurations when rustc is
+bootstrapped in rust oe-selftest.
+
+Upstream-Status: Backport [https://github.com/rust-lang/rust/pull/119619/commits/26c71cbcf1a9bce6ceb962d753c467d098f63cf6]
+
+Signed-off-by: onur-ozkan <work@onurozkan.dev>
+Signed-off-by: Yash Shinde <Yash.Shinde@windriver.com>
+---
+diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
+index e85f6319936..c45c0b3c652 100644
+--- a/src/tools/compiletest/src/common.rs
++++ b/src/tools/compiletest/src/common.rs
+@@ -479,6 +479,7 @@ fn new(config: &Config) -> TargetCfgs {
+         let mut targets: HashMap<String, TargetCfg> = serde_json::from_str(&rustc_output(
+             config,
+             &["--print=all-target-specs-json", "-Zunstable-options"],
++            Default::default(),
+         ))
+         .unwrap();
+
+@@ -491,16 +492,33 @@ fn new(config: &Config) -> TargetCfgs {
+         let mut all_families = HashSet::new();
+         let mut all_pointer_widths = HashSet::new();
+
+-        // Handle custom target specs, which are not included in `--print=all-target-specs-json`.
+-        if config.target.ends_with(".json") {
+-            targets.insert(
+-                config.target.clone(),
+-                serde_json::from_str(&rustc_output(
+-                    config,
+-                    &["--print=target-spec-json", "-Zunstable-options", "--target", &config.target],
+-                ))
+-                .unwrap(),
+-            );
++        // If current target is not included in the `--print=all-target-specs-json` output,
++        // we check whether it is a custom target from the user or a synthetic target from bootstrap.
++        if !targets.contains_key(&config.target) {
++            let mut envs: HashMap<String, String> = HashMap::new();
++
++            if let Ok(t) = std::env::var("RUST_TARGET_PATH") {
++                envs.insert("RUST_TARGET_PATH".into(), t);
++            }
++
++            // This returns false only when the target is neither a synthetic target
++            // nor a custom target from the user, indicating it is most likely invalid.
++            if config.target.ends_with(".json") || !envs.is_empty() {
++                targets.insert(
++                    config.target.clone(),
++                    serde_json::from_str(&rustc_output(
++                        config,
++                        &[
++                            "--print=target-spec-json",
++                            "-Zunstable-options",
++                            "--target",
++                            &config.target,
++                        ],
++                        envs,
++                    ))
++                    .unwrap(),
++                );
++            }
+         }
+
+         for (target, cfg) in targets.iter() {
+@@ -545,7 +563,9 @@ fn get_current_target_config(
+         // code below extracts them from `--print=cfg`: make sure to only override fields that can
+         // actually be changed with `-C` flags.
+         for config in
+-            rustc_output(config, &["--print=cfg", "--target", &config.target]).trim().lines()
++            rustc_output(config, &["--print=cfg", "--target", &config.target], Default::default())
++                .trim()
++                .lines()
+         {
+             let (name, value) = config
+                 .split_once("=\"")
+@@ -624,11 +644,12 @@ pub enum Endian {
+     Big,
+ }
+
+-fn rustc_output(config: &Config, args: &[&str]) -> String {
++fn rustc_output(config: &Config, args: &[&str], envs: HashMap<String, String>) -> String {
+     let mut command = Command::new(&config.rustc_path);
+     add_dylib_path(&mut command, iter::once(&config.compile_lib_path));
+     command.args(&config.target_rustcflags).args(args);
+     command.env("RUSTC_BOOTSTRAP", "1");
++    command.envs(envs);
+
+     let output = match command.output() {
+         Ok(output) => output,
+