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Greatly reduce amount of debuginfo compiled for bootstrap itself #89756

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Oct 12, 2021
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Greatly reduce amount of debuginfo compiled for bootstrap itself #89756

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9 changes: 9 additions & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,15 @@ gimli.debug = 0
miniz_oxide.debug = 0
object.debug = 0

# The only package that ever uses debug builds is bootstrap.
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This feels a little adhoc and not terribly future proof. I think custom profiles are stable or will be quite soon, maybe we can use that?

FWIW I think we haven't had panics and such from bootstrap in a while, so maybe we can just disable debuginfo fully...

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I find debuginfo useful when modifying bootstrap itself, but I guess it's not too hard to add it back in in bootstrap.py if necessary. I don't think it would make this much simpler though, we definitely don't want to disable debuginfo for anything besides bootstrap.

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Hmm, adding the named-profiles feature breaks x.py because it doesn't pass RUSTC_BOOTSTRAP for building bootstrap itself. Also I think this would prevent people from running cargo metadata with anything other than nightly.

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@jyn514 Is it currently guaranteed that e.g. running cargo metadata on rustc with a stable compiler will always work? For example right now it doesn't work, because the stable compiler misses edition 2021, which is used by src/bootstrap/Cargo.toml.

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It's not guaranteed, but it does work most of the time.

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OK, I've thought a little more about this and it seems OK to me to do this as-is. It's fairly minimal still, and hopefully as you say won't affect anything else. We could try to be a little more minimal by setting this via the env variable (CARGO_PROFILE_<name>_DEBUG) but it doesn't seem particularly necessary so we can just do this for now.

# We care a lot about bootstrap's compile times, so don't include debug info for
# dependencies, only bootstrap itself.
[profile.dev]
debug = 0
[profile.dev.package]
# Only use debuginfo=1 to further reduce compile times.
bootstrap.debug = 1

# We want the RLS to use the version of Cargo that we've got vendored in this
# repository to ensure that the same exact version of Cargo is used by both the
# RLS and the Cargo binary itself. The RLS depends on Cargo as a git repository
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3 changes: 1 addition & 2 deletions src/bootstrap/bootstrap.py
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Expand Up @@ -921,10 +921,9 @@ def build_bootstrap(self):
env["LIBRARY_PATH"] = os.path.join(self.bin_root(True), "lib") + \
(os.pathsep + env["LIBRARY_PATH"]) \
if "LIBRARY_PATH" in env else ""

# preserve existing RUSTFLAGS
env.setdefault("RUSTFLAGS", "")
env["RUSTFLAGS"] += " -Cdebuginfo=2"

build_section = "target.{}".format(self.build)
target_features = []
if self.get_toml("crt-static", build_section) == "true":
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