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Add a comment why extern crate is necessary for rustdoc #76728

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Sep 16, 2020
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Add a comment why extern crate is necessary for rustdoc #76728

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Add a comment why `extern crate` is necessary for rustdoc
jyn514 Sep 15, 2020
b93a831
Add a comment why rustdoc loads crates from the sysroot
jyn514 Sep 15, 2020
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8 changes: 6 additions & 2 deletions src/librustdoc/lib.rs
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Expand Up @@ -16,6 +16,12 @@

#[macro_use]
extern crate lazy_static;
#[macro_use]
extern crate tracing;

// N.B. these need `extern crate` even in 2018 edition
// because they're loaded implicitly from the sysroot.
// Dependencies listed in Cargo.toml do not need extern crate.
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So the question now is why does rustdoc have to search dependencies in sysroot rather than specify them in Cargo.toml.

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I think it's because we don't build it in the rustc cargo directory, in part because that gives us finer-grained deleting. That means if we specified things in Cargo.toml, we'd end up rebuilding rustc crates.

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I updated the comment to mention why rustdoc uses the sysroot instead of cargo.toml.

extern crate rustc_ast;
extern crate rustc_ast_pretty;
extern crate rustc_attr;
Expand All @@ -42,8 +48,6 @@ extern crate rustc_target;
extern crate rustc_trait_selection;
extern crate rustc_typeck;
extern crate test as testing;
#[macro_use]
extern crate tracing;

use std::default::Default;
use std::env;
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