[PATCH 1/2] docs: rust: update instructions for obtaining 'core' source

[Trevor Gross <tmgross@umich.edu>]

The source for Rust's 'core' library is needed to build the kernel with
Rust support. This must be obtained manually when using a non-rustup
install, such as when using 'rustc' from a package manager or from a
standalone installer. Currently, the documentation suggests cloning the
'rust' repository to obtain these sources, but this is quite slow (on
the order of a few minutes).

This patch changes this documentation to suggest using the source
tarball instead, which includes only needed information (<5M) and is
significantly faster to download. This is more in line with what
'rustup' does.

Signed-off-by: Trevor Gross <tmgross@umich.edu>
---
 Documentation/rust/quick-start.rst | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/Documentation/rust/quick-start.rst b/Documentation/rust/quick-start.rst
index a8931512ed98..bb67deb19100 100644
--- a/Documentation/rust/quick-start.rst
+++ b/Documentation/rust/quick-start.rst
@@ -56,16 +56,17 @@ If ``rustup`` is being used, run::
 The components are installed per toolchain, thus upgrading the Rust compiler
 version later on requires re-adding the component.
 
-Otherwise, if a standalone installer is used, the Rust repository may be cloned
-into the installation folder of the toolchain::
+Otherwise, if a standalone installer is used, the Rust source tree may be
+downloaded into the toolchain's installation folder::
 
-	git clone --recurse-submodules \
-		--branch $(scripts/min-tool-version.sh rustc) \
-		https://github.com/rust-lang/rust \
-		$(rustc --print sysroot)/lib/rustlib/src/rust
+	curl -L https://static.rust-lang.org/dist/rust-src-$(scripts/min-tool-version.sh rustc).tar.gz |
+		tar -xzf - -C $(rustc --print sysroot)/lib \
+		rust-src-$(scripts/min-tool-version.sh rustc)/rust-src/lib/ \
+		--strip-components=3
 
 In this case, upgrading the Rust compiler version later on requires manually
-updating this clone.
+updating the source tree (this can be done by removing ``$(rustc --print
+sysroot)/lib/rustlib/src/rust`` then rerunning the above command).
 
 
 libclang
-- 
2.34.1