Merge #9752

9752: feature: Declare proc-macro dependent crates in `rust-project.json` r=matklad a=tobywf

This adds the `is_proc_macro` flag in `rust-project.json`. By default, this is `false` and not required, so existing projects won't break/have the same behavior as before this change. If the flag is true, a dependency to the `proc_macro` sysroot crate is added (if it exists), so that rust-analyzer can resolve those imports.

This fixes #9726 .

I've also added some tests in the second commit. The first is a smoke test for a basic, minimal `rust-project.json` file. The second is a more targeted test for the flag. Both tests depend on the fake sysroot (a bunch of directories in the correct layout with empty `lib.rs` files), and also on `env!("CARGO_MANIFEST_DIR")` being an absolute path. I'm not sure if the later assumption is valid on all platforms. I wanted to at least try and add tests, but I'm happy to rework them or remove them if you don't think that's the way to go.

(You can license/relicense my contribution in any way you wish without contacting me.)

Co-authored-by: Toby Fleming <sourcecode@tobywf.com>

Author: bors[bot]

crates/project_model/src/project_json.rs

@@ -37,6 +37,7 @@ pub struct Crate {
     pub(crate) is_workspace_member: bool,
     pub(crate) include: Vec<AbsPathBuf>,
     pub(crate) exclude: Vec<AbsPathBuf>,
+    pub(crate) is_proc_macro: bool,
 }
 
 impl ProjectJson {
@@ -96,6 +97,7 @@ impl ProjectJson {
                         is_workspace_member,
                         include,
                         exclude,
+                        is_proc_macro: crate_data.is_proc_macro,
                     }
                 })
                 .collect::<Vec<_>>(),
@@ -135,6 +137,8 @@ struct CrateData {
     proc_macro_dylib_path: Option<PathBuf>,
     is_workspace_member: Option<bool>,
     source: Option<CrateSource>,
+    #[serde(default)]
+    is_proc_macro: bool,
 }
 
 #[derive(Deserialize, Debug, Clone)]