rust: Support latest version of `rust-analyzer`

Sets the `sysroot` field in rust-project.json which is now needed in
newer versions of rust-analyzer instead of the `sysroot_src` field.

Till [1] `rust-analyzer` used to guess the `sysroot` based on the
`sysroot_src` at [2]. Now `sysroot` is a required parameter for a
`rust-project.json` file. It is required because `rust-analyzer`
need it to find the proc-macro server [3].

In the current version of `rust-analyzer` the `sysroot_src` is only used
to include the inbuilt library crates (std, core, alloc, etc) [4]. Since
we already specify the core library to be included in the
`rust-project.json` we don't need to define the `sysroot_src`.

Code editors like VS Code try to use the latest version of rust-analyzer
(which is updated every week) instead of the version of rust-analyzer
that comes with the rustup toolchain (which is updated every six weeks
along with the rust version).

Without this change `rust-analyzer` is breaking for anyone using VS Code.
As they are getting the latest version of `rust-analyzer` with the
changes made in [1].

`rust-analyzer` will also start breaking for other developers as they
update their rust version (assuming that also updates the rust-analyzer
version on their system).

This patch should work with every setup as there is no more guess work
being done by `rust-analyzer`.

[ Lukas, who leads the rust-analyzer team, says:

    `sysroot_src` is required now if you want to have the sysroot
    source libraries be loaded. I think we used to infer it as
    `{sysroot}/lib/rustlib/src/rust/library` before when only the
    `sysroot` field was given but that was since changed to make it
    possible in having a sysroot without the standard library sources
    (that is only have the binaries available). So if you want the
    library sources to be loaded by rust-analyzer you will have to set
    that field as well now.

  - Miguel ]

Link: https://github.com/rust-lang/rust-analyzer/pull/17287 [1]
Link: https://github.com/rust-lang/rust-analyzer/blob/f372a8a1176ff8dd5f45ab2ddd45f3530db0374f/crates/project-model/src/workspace.rs#L367-L374 [2]
Link: https://github.com/rust-lang/rust-analyzer/blob/eeb192b79aeac47b40add66347022af17a74fbaf/crates/project-model/src/sysroot.rs#L180-L192 [3]
Link: https://github.com/search?q=repo%3AVeykril%2Frust-analyzer%20src_root()&type=code [4]
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Sarthak Singh <sarthak.singh99@gmail.com>
Link: https://rust-for-linux.zulipchat.com/#narrow/stream/291565-Help/topic/How.20to.20rust-analyzer.20correctly.20working
Link: https://lore.kernel.org/r/20240724172713.899399-1-sarthak.singh99@gmail.com
[ Formatted comment, fixed typo and removed spurious empty line. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/Makefile

@@ -350,7 +350,7 @@ rust-analyzer:
 	$(Q)$(srctree)/scripts/generate_rust_analyzer.py \
 		--cfgs='core=$(core-cfgs)' --cfgs='alloc=$(alloc-cfgs)' \
 		$(realpath $(srctree)) $(realpath $(objtree)) \
-		$(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
+		$(rustc_sysroot) $(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
 		$(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
 
 redirect-intrinsics = \

scripts/generate_rust_analyzer.py

@@ -145,6 +145,7 @@ def main():
     parser.add_argument('--cfgs', action='append', default=[])
     parser.add_argument("srctree", type=pathlib.Path)
     parser.add_argument("objtree", type=pathlib.Path)
+    parser.add_argument("sysroot", type=pathlib.Path)
     parser.add_argument("sysroot_src", type=pathlib.Path)
     parser.add_argument("exttree", type=pathlib.Path, nargs="?")
     args = parser.parse_args()
@@ -154,9 +155,12 @@ def main():
         level=logging.INFO if args.verbose else logging.WARNING
     )
 
+    # Making sure that the `sysroot` and `sysroot_src` belong to the same toolchain.
+    assert args.sysroot in args.sysroot_src.parents
+
     rust_project = {
         "crates": generate_crates(args.srctree, args.objtree, args.sysroot_src, args.exttree, args.cfgs),
-        "sysroot_src": str(args.sysroot_src),
+        "sysroot": str(args.sysroot),
     }
 
     json.dump(rust_project, sys.stdout, sort_keys=True, indent=4)