scripts: generate_rust_analyzer: add missing macros deps

The macros crate has depended on std and proc_macro since its
introduction in commit 1fbde52bde73 ("rust: add `macros` crate"). These
dependencies were omitted from commit 8c4555ccc55c ("scripts: add
`generate_rust_analyzer.py`") resulting in missing go-to-definition and
autocomplete, and false-positive warnings emitted from rust-analyzer
such as:

[{
"resource": "/Users/tamird/src/linux/rust/macros/module.rs",
"owner": "_generated_diagnostic_collection_name_#1",
"code": {
"value": "non_snake_case",
"target": {
"$mid": 1,
"path": "/rustc/",
"scheme": "https",
"authority": "doc.rust-lang.org",
"query": "search=non_snake_case"
}
},
"severity": 4,
"message": "Variable `None` should have snake_case name, e.g. `none`",
"source": "rust-analyzer",
"startLineNumber": 123,
"startColumn": 17,
"endLineNumber": 123,
"endColumn": 21
}]

Add the missing dependencies to improve the developer experience.

[ Fiona had a different approach (thanks!) at:

https://lore.kernel.org/rust-for-linux/[e-mail]/

But Tamir and Fiona agreed to this one. - Miguel ]

Fixes: 8c4555ccc55c ("scripts: add `generate_rust_analyzer.py`")
Reviewed-by: Fiona Behrens <[e-mail]>
Diagnosed-by: Chayim Refael Friedman <[e-mail]>
Link: https://github.com/rust-lang/rust-analyzer/issues/17759#issuecomment-2646328275
Signed-off-by: Tamir Duberstein <[e-mail]>
Tested-by: Andreas Hindborg <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[ Removed `return`. Changed tag name. Added Link. Slightly
reworded. - Miguel ]
Signed-off-by: Miguel Ojeda <[e-mail]>

scripts/generate_rust_analyzer.py

···
         crates_indexes[display_name] = len(crates)
         crates.append(crate)
 
-    # First, the ones in `rust/` since they are a bit special.
-    append_crate(
-        "core",
-        sysroot_src / "core" / "src" / "lib.rs",
-        [],
-        cfg=crates_cfgs.get("core", []),
-        is_workspace_member=False,
-    )
+    def append_sysroot_crate(
+        display_name,
+        deps,
+        cfg=[],
+    ):
+        append_crate(
+            display_name,
+            sysroot_src / display_name / "src" / "lib.rs",
+            deps,
+            cfg,
+            is_workspace_member=False,
+        )
+
+    # NB: sysroot crates reexport items from one another so setting up our transitive dependencies
+    # here is important for ensuring that rust-analyzer can resolve symbols. The sources of truth
+    # for this dependency graph are `(sysroot_src / crate / "Cargo.toml" for crate in crates)`.
+    append_sysroot_crate("core", [], cfg=crates_cfgs.get("core", []))
+    append_sysroot_crate("alloc", ["core"])
+    append_sysroot_crate("std", ["alloc", "core"])
+    append_sysroot_crate("proc_macro", ["core", "std"])
 
     append_crate(
         "compiler_builtins",
···
     append_crate(
         "macros",
         srctree / "rust" / "macros" / "lib.rs",
-        [],
+        ["std", "proc_macro"],
         is_proc_macro=True,
     )