Add llvm-ir subtarget for rust rules

Summary: This was useful in debugging S443733.

Reviewed By: dtolnay

Differential Revision: D62049233

fbshipit-source-id: c64d1f5b18fb1bb4c1d140c9bb60b1c427bac71c

prelude/rust/build.bzl

@@ -1217,6 +1217,9 @@ def _explain(crate_type: CrateType, link_strategy: LinkStrategy, emit: Emit, inf
     if emit == Emit("expand"):
         return "expand"
 
+    if emit == Emit("llvm-ir"):
+        return "llvm-ir"
+
     fail("unrecognized rustc action:", crate_type, link_strategy, emit)
 
 EmitOperation = record(

prelude/rust/rust_binary.bzl

@@ -323,16 +323,17 @@ def _rust_binary_common(
     incr_enabled = ctx.attrs.incremental_enabled
     extra_compiled_targets.update(output_as_diag_subtargets(diag_artifacts[incr_enabled], clippy_artifacts[incr_enabled]))
 
-    expand = rust_compile(
-        ctx = ctx,
-        compile_ctx = compile_ctx,
-        emit = Emit("expand"),
-        params = strategy_param[DEFAULT_STATIC_LINK_STRATEGY],
-        default_roots = default_roots,
-        extra_flags = extra_flags,
-        incremental_enabled = ctx.attrs.incremental_enabled,
-    )
-    extra_compiled_targets["expand"] = expand.output
+    for emit in ("expand", "llvm-ir"):
+        compile = rust_compile(
+            ctx = ctx,
+            compile_ctx = compile_ctx,
+            emit = Emit(emit),
+            params = strategy_param[DEFAULT_STATIC_LINK_STRATEGY],
+            default_roots = default_roots,
+            extra_flags = extra_flags,
+            incremental_enabled = ctx.attrs.incremental_enabled,
+        )
+        extra_compiled_targets[emit] = compile.output
 
     doc_output = generate_rustdoc(
         ctx = ctx,

prelude/rust/rust_library.bzl

@@ -246,6 +246,15 @@ def rust_library_impl(ctx: AnalysisContext) -> list[Provider]:
         incremental_enabled = ctx.attrs.incremental_enabled,
     )
 
+    llvm_ir = rust_compile(
+        ctx = ctx,
+        compile_ctx = compile_ctx,
+        emit = Emit("llvm-ir"),
+        params = static_library_params,
+        default_roots = default_roots,
+        incremental_enabled = ctx.attrs.incremental_enabled,
+    )
+
     # If doctests=True or False is set on the individual target, respect that.
     # Otherwise look at the global setting on the toolchain.
     doctests_enabled = \
@@ -308,6 +317,7 @@ def rust_library_impl(ctx: AnalysisContext) -> list[Provider]:
         check_artifacts = output_as_diag_subtargets(diag_artifacts[incr_enabled], clippy_artifacts[incr_enabled]),
         expand = expand.output,
         sources = compile_ctx.symlinked_srcs,
+        llvm_ir = llvm_ir.output,
         rustdoc_coverage = rustdoc_coverage,
         named_deps_names = write_named_deps_names(ctx, compile_ctx),
     )
@@ -519,6 +529,7 @@ def _default_providers(
         check_artifacts: dict[str, Artifact | None],
         expand: Artifact,
         sources: Artifact,
+        llvm_ir: Artifact,
         rustdoc_coverage: Artifact,
         named_deps_names: Artifact | None) -> list[Provider]:
     targets = {}
@@ -527,6 +538,7 @@ def _default_providers(
     targets["expand"] = expand
     targets["doc"] = rustdoc
     targets["doc-coverage"] = rustdoc_coverage
+    targets["llvm-ir"] = llvm_ir
     if named_deps_names:
         targets["named_deps"] = named_deps_names
     sub_targets = {