Merge from rustc

1 files changed, 18 insertions, 2 deletions

diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index fea194a80ef..28d96cb1cfe 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -917,8 +917,24 @@ class RustBuild(object):
             if toml_val is not None:
                 env["{}_{}".format(var_name, host_triple_sanitized)] = toml_val
 
-        # preserve existing RUSTFLAGS
-        env.setdefault("RUSTFLAGS", "")
+        # In src/etc/rust_analyzer_settings.json, we configure rust-analyzer to
+        # pass RUSTC_BOOTSTRAP=1 to all cargo invocations because the standard
+        # library uses unstable Cargo features. Without RUSTC_BOOTSTRAP,
+        # rust-analyzer would fail to fetch workspace layout when the system's
+        # default toolchain is not nightly.
+        #
+        # But that setting has the collateral effect of rust-analyzer also
+        # passing RUSTC_BOOTSTRAP=1 to all x.py invocations too (the various overrideCommand).
+        # For compiling bootstrap that can cause spurious rebuilding of bootstrap when
+        # rust-analyzer x.py invocations are interleaved with handwritten ones on the
+        # command line.
+        #
+        # Set RUSTC_BOOTSTRAP=1 consistently.
+        env["RUSTC_BOOTSTRAP"] = "1"
+
+        default_rustflags = "" if env.get("RUSTFLAGS_BOOTSTRAP", "") else "-Zallow-features="
+
+        env.setdefault("RUSTFLAGS", default_rustflags)
 
         target_features = []
         if self.get_toml("crt-static", build_section) == "true":