add Prepare base builder and Running checks sections

docs/src/guides/languages/rust.md

@@ -44,4 +44,73 @@ Also we will take a look how we are setup Rust projects and what configuration i
     [example](https://github.com/input-output-hk/catalyst-ci/blob/master/examples/rust/Earthfile).
 <!-- markdownlint-enable max-one-sentence-per-line -->
 
-### Prepare base builder
+### Prepare base builder
+
+
+```Earthfile
+VERSION 0.7
+
+# Set up our target toolchains, and copy our files.
+builder:
+    FROM ./../../earthly/rust+rust-base
+    
+    COPY --dir "*" .
+    DO ./../../earthly/rust+SETUP
+```
+
+The first target `builder` is responsible for preparing an already configured Rust environment,
+instal all needed tools and dependencies.
+
+The fist step of the `builder` target is to prepare a Rust environment via `+rust-base` target.
+Next step is to copy source code of the project and finally finalize the build
+which is done with `+SETUP` UDC target.
+The `+SETUP` UDC target requires to have a `rust-toolchain.toml` file,
+with the specified `channel` option in it.
+
+### Running checks
+
+```Earthfile
+# Test rust build container - Use best architecture host tools.
+check-hosted:
+    FROM +builder
+
+    DO ./../../earthly/rust+CHECK
+
+# Test which runs check with all supported host tooling.  Needs qemu or rosetta to run.
+# Only used to validate tooling is working across host toolsets.
+check-all-hosts:    
+    BUILD --platform=linux/amd64 --platform=linux/arm64 +check-hosted
+
+## Standard CI targets.
+##
+## These targets are discovered and executed automatically by CI.
+
+# Run check using the most efficient host tooling
+# CI Automated Entry point.
+check:
+    FROM busybox
+    # This is necessary to pick the correct architecture build to suit the native machine.
+    # It primarily ensures that Darwin/Arm builds work as expected without needing x86 emulation.
+    # All target implementation of this should follow this pattern.
+    ARG USERARCH
+
+    IF [ "$USERARCH" == "arm64" ]
+        BUILD --platform=linux/arm64 +check-hosted
+    ELSE
+        BUILD --platform=linux/amd64 +check-hosted
+    END
+```
+
+With prepared environment and all data, we're now ready to start operating with the source code and configuration files.
+The `check-hosted` target which actually performs all checks and validation
+with the help of `+CHECK` UDC target.
+The `+CHECK` UDC target performs static checks of the Rust project as `cargo fmt`, `cargo machete`, `cargo deny` which will validate formatting, find unused dependencies and any supply chain issues with dependencies.
+Also during it validates configuration files as `.cargo/config.toml`, `rustfmt.toml`, `.config/nextest.toml`, `clippy.toml`, `deny.toml`
+to be the same as defined in `earthly/rust/stdcfgs` directory of the `catalyst-ci` repo.
+
+Another targets as `check-all-hosts` and `check` (running on CI) just invoke `check-hosted`
+with the specified `--platform`.
+It is important to define a `linux` target platform with a proper cpu architecture
+for the Rust project when you are building it inside Docker
+and check the build process with different scenarios.
+The same approach we will see for the another targets of this guide.

earthly/rust/Earthfile

@@ -66,6 +66,7 @@ rust-base-all-hosts:
 SETUP:
     COMMAND
 
+    COPY ./rust-toolchain.toml .
     ENV default_rust_channel=$(rg -oP 'channel\s*=\s*"\K[^"]+' rust-toolchain.toml)
 
     # Check that `default_rust_channel` and $RUST_VERSION from the rust-base container are exactly the same.

examples/rust/Earthfile

@@ -3,9 +3,8 @@ VERSION 0.7
 # Set up our target toolchains, and copy our files.
 builder:
     FROM ./../../earthly/rust+rust-base
-
-    COPY --dir "*" .
 
+    COPY --dir "*" .
     DO ./../../earthly/rust+SETUP
 
 # Test rust build container - Use best architecture host tools.