1 files changed, 82 insertions, 0 deletions
diff --git a/src/bootstrap/synthetic_targets.rs b/src/bootstrap/synthetic_targets.rs
new file mode 100644
index 000000000..7eeac9025
--- /dev/null
+++ b/src/bootstrap/synthetic_targets.rs
@@ -0,0 +1,82 @@
+//! In some cases, parts of bootstrap need to change part of a target spec just for one or a few
+//! steps. Adding these targets to rustc proper would "leak" this implementation detail of
+//! bootstrap, and would make it more complex to apply additional changes if the need arises.
+//!
+//! To address that problem, this module implements support for "synthetic targets". Synthetic
+//! targets are custom target specs generated using builtin target specs as their base. You can use
+//! one of the target specs already defined in this module, or create new ones by adding a new step
+//! that calls create_synthetic_target.
+
+use crate::builder::{Builder, ShouldRun, Step};
+use crate::config::TargetSelection;
+use crate::Compiler;
+use std::process::{Command, Stdio};
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub(crate) struct MirOptPanicAbortSyntheticTarget {
+    pub(crate) compiler: Compiler,
+    pub(crate) base: TargetSelection,
+}
+
+impl Step for MirOptPanicAbortSyntheticTarget {
+    type Output = TargetSelection;
+    const DEFAULT: bool = true;
+    const ONLY_HOSTS: bool = false;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.never()
+    }
+
+    fn run(self, builder: &Builder<'_>) -> Self::Output {
+        create_synthetic_target(builder, self.compiler, "miropt-abort", self.base, |spec| {
+            spec.insert("panic-strategy".into(), "abort".into());
+        })
+    }
+}
+
+fn create_synthetic_target(
+    builder: &Builder<'_>,
+    compiler: Compiler,
+    suffix: &str,
+    base: TargetSelection,
+    customize: impl FnOnce(&mut serde_json::Map<String, serde_json::Value>),
+) -> TargetSelection {
+    if base.contains("synthetic") {
+        // This check is not strictly needed, but nothing currently needs recursive synthetic
+        // targets. If the need arises, removing this in the future *SHOULD* be safe.
+        panic!("cannot create synthetic targets with other synthetic targets as their base");
+    }
+
+    let name = format!("{base}-synthetic-{suffix}");
+    let path = builder.out.join("synthetic-target-specs").join(format!("{name}.json"));
+    std::fs::create_dir_all(path.parent().unwrap()).unwrap();
+
+    if builder.config.dry_run() {
+        std::fs::write(&path, b"dry run\n").unwrap();
+        return TargetSelection::create_synthetic(&name, path.to_str().unwrap());
+    }
+
+    let mut cmd = Command::new(builder.rustc(compiler));
+    cmd.arg("--target").arg(base.rustc_target_arg());
+    cmd.args(["-Zunstable-options", "--print", "target-spec-json"]);
+    cmd.stdout(Stdio::piped());
+
+    let output = cmd.spawn().unwrap().wait_with_output().unwrap();
+    if !output.status.success() {
+        panic!("failed to gather the target spec for {base}");
+    }
+
+    let mut spec: serde_json::Value = serde_json::from_slice(&output.stdout).unwrap();
+    let spec_map = spec.as_object_mut().unwrap();
+
+    // The `is-builtin` attribute of a spec needs to be removed, otherwise rustc will complain.
+    spec_map.remove("is-builtin");
+
+    customize(spec_map);
+
+    std::fs::write(&path, &serde_json::to_vec_pretty(&spec).unwrap()).unwrap();
+    let target = TargetSelection::create_synthetic(&name, path.to_str().unwrap());
+    crate::cc_detect::find_target(builder, target);
+
+    target
+}