Add internal RUSTC_INTERNAL_FORCE_PANIC_ABORT env var for libpanic_abort

src/bootstrap/bin/rustc.rs

@@ -94,6 +94,11 @@ fn main() {
         // other crate intentionally as this is the only crate for now that we
         // ship with panic=abort.
         //
+        // FIXME: Remove the special case for "panic_abort"
+        // once https://github.com/rust-lang/rust/pull/60026
+        // rides the release train into the bootstrap compiler.
+        // `cfg(bootstrap)`: (added to make this easier to grep for)
+        //
         // This... is a bit of a hack how we detect this. Ideally this
         // information should be encoded in the crate I guess? Would likely
         // require an RFC amendment to RFC 1513, however.

src/libpanic_abort/build.rs

@@ -0,0 +1,7 @@
+fn main() {
+    // Hack to force this crate to be compiled with the `abort`
+    // panic strategy, regardless of what strategy Cargo
+    // passes to the compiler.
+    // See `rustc::session::Session::panic_strategy` for more details
+    println!("cargo:rustc-env=RUSTC_INTERNAL_FORCE_PANIC_ABORT=1");
+}

src/librustc/session/mod.rs

@@ -563,6 +563,18 @@ impl Session {
     /// Returns the panic strategy for this compile session. If the user explicitly selected one
     /// using '-C panic', use that, otherwise use the panic strategy defined by the target.
     pub fn panic_strategy(&self) -> PanicStrategy {
+        // This is a hack to support `libpanic_abort`. We require `libpanic_abort`
+        // to always be built with `PanicStrategy::Abort`, regardless of what panic
+        // strategy is suppplied to the compiler. Ideally, this would be an intenral
+        // attribute in `libpanic_abort` - howevver, emscripten needs to access
+        // the panic strategy before we even start parsing the crate:
+        // https://github.com/rust-lang/rust/blob/3fc30d8/src/librustc_codegen_llvm/llvm_util.rs#L77
+        //
+        // As a result, we need to use a special environment variable, which is set from
+        // the `build.rs` of `libpanic_abort`
+        if env::var("RUSTC_INTERNAL_FORCE_PANIC_ABORT").is_ok() {
+            return PanicStrategy::Abort;
+        }
         self.opts
             .cg
             .panic