JSON-based workspaces don't detect or read target data layout?

Question

Looks like JSON-based workspace doesn't have an equivalent of target_layout filed as in Cargo-based ones?

https://github.com/rust-lang/rust-analyzer/blob/237ffa3997250b8569ced477a5072310eb48c847/crates/project-model/src/workspace.rs#L70-L93

So when creating the crate graph here, we pass in an Err:

https://github.com/rust-lang/rust-analyzer/blob/237ffa3997250b8569ced477a5072310eb48c847/crates/project-model/src/workspace.rs#L622

May I know whether this is intentional, or perhaps at least a FIXME should be tagged at this line?

Observed effects

#8813 won't work in JSON-based workspaces, e.g.

let _x = [true; 100];
  //^^ [bool; _] 

the length part is still Unknown thus displayed as an underscore.

Possible solutions? (if we are to fix it)

• reuse this target_data_layout::get() function for JSON-based workspaces?

  https://github.com/rust-lang/rust-analyzer/blob/237ffa3997250b8569ced477a5072310eb48c847/crates/project-model/src/target_data_layout.rs#L15-L37

  By the way, in this function there are two attempts of issuing rustc command. It looks to me the only difference between them is to cd <project root> or not. Idk, will the existence of Cargo.toml in the current directory affect the result of rustc +nightly -Z unstable-options --print target-spec-json?

• derive the data layout information from this provided triple?

  https://github.com/rust-lang/rust-analyzer/blob/62c81d62932c458e23975191ecc124916be0b35e/crates/project-model/src/project_json.rs#L83

Thanks for your effort!

Start in crates/project-model/src/workspace.rs, especially the workspace data definitions and crate-graph construction around the referenced lines. Read target_data_layout.rs and project_json.rs to compare Cargo-based and JSON-based handling, then reproduce the provided [true; 100] example. Done means JSON-based workspaces provide the needed layout information so the array length is no longer displayed as Unknown.