# Description

`substrate-wasm-builder` can be a build dependency for crates which
develop FRAME runtimes. I had a tough time seeing errors happening in
such crates (e.g. runtimes from the `templates` directory) in my IDE. I
use a combination of rust-analyzer + nvim-lsp + nvim-lspconfig +
rustacean.vim and all of this stack is not able to correctly parse
errors emitted during the `build` phase.

As a matter of fact there is also a cargo issue tracking specifically
this issue where cargo doesn't propagate the `--message-format` type to
the build phase: [here](https://github.com/rust-lang/cargo/issues/14246)
initially and then
[here](https://github.com/rust-lang/cargo/issues/8283). It feels like a
solution for this use case isn't very close, so if it comes to runtimes
development (both as an SDK user and developer), enabling wasm builder
to emit diagnostics messages friendly to IDEs would be useful for
regular workflows where IDEs are used for finding errors instead of
manually running `cargo` commands.

## Integration

It can be an issue if Substrate/FRAME SDKs users and developers rely on
the runtimes' crates build phase output in certain ways. Emitting
compilation messages as json will pollute the regular compilation output
so people that would manually run `cargo build` or `cargo check` on
their crates will have a tougher time extracting the non JSON output.

## Review Notes

Rust IDEs based on rust-analyzer rely on cargo check/clippy to extract
diagnostic information. The information is generated by passing flags
like `--messages-format=json` to the `cargo` commands. The messages are
extracted by rust-analyzer and published to LSP clients that will
populate UIs accordingly.

We need to build against the wasm target by using `message-format=json`
too so that IDEs can show the errors for crates that have a build
dependency on `substrate-wasm-builder`.

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Signed-off-by: Iulian Barbu <iulian.barbu@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>