Make the update check an optional feature

[virzak]

The update check contacts crates.io on every run and pulls in update-informer with an HTTP and TLS stack. This moves it out of the cli feature into a new update-check feature, which is enabled by default, so nothing changes for cargo install espflash.

Distributions can now build the CLI without it via --no-default-features --features cli. OpenWrt asked for exactly that when packaging espflash (openwrt/packages#30659). There it also takes about 1 MB off the binary.

--skip-update-check is kept, so scripts that pass it keep working when the feature is off.

[SergioGasquez]

I like the change, but, in theory, it would require a major version bump. Although I don't think any library user would be affected by this change.

A minor-compatible alternative: keep pub mod update gated on cli, and gate only the dependency and the function body on update-check:

  /// Check for updates
  #[cfg(feature = "cli")]
  pub mod update {
      /// Check for updates to the espflash crate.
      ///
      /// Does nothing unless the `update-check` feature is enabled.
      pub fn check_for_update(name: &str, version: &str) {
          #[cfg(feature = "update-check")]
          {
              use std::time::Duration;

              use log::info;
              use update_informer::{Check, registry::Crates};

              let informer =
                  update_informer::new(Crates, name, version).interval(Duration::from_secs(0));
              if let Some(version) = informer.check_version().ok().flatten() {
                  info!("🚀 A new version of {name} is available: {version}");
              }
          }
          #[cfg(not(feature = "update-check"))]
          let _ = (name, version);
      }
  }

This would still drop the HTTP and TSL stack on OpenWrt build.

We still have to decide if the next espflash version would be 5.0.0 or a minor version. We will have a plan for this at the end of the mont

[virzak]

Good point, done in 247ef74: update and check_for_update() stay under cli, only the update-informer call is gated on update-check, and the binary change is reverted. Built with --no-default-features --features cli the binary still has no HTTP/TLS code.

[SergioGasquez]

Currently we dont test this config, we should add

  - run: RUSTFLAGS="-D warnings" cargo check -p espflash --no-default-features --features cli

To https://github.com/esp-rs/espflash/blob/main/.github/workflows/ci.yml#L89-L90

[SergioGasquez]

Suggested change

	update-check = ["dep:update-informer"]
	update-check = ["cli", "dep:update-informer"]

Otherwise update-check doesn't turn on cli and with --no-default-features --features update-check, the dependency gets pulled in but the update module isn't compiled.

[virzak]

Applied in 267d78b, together with the CI step for --no-default-features --features cli.