Simplify build.py for Rust

This commit attempts to simplify a bit Rust builds.
In essence it derives the channel to use depending on the WASI
version. This make the invocation a bit more uniform across other
language builders.

Author: saulecabrera

.github/workflows/compile-tests.yml

@@ -66,7 +66,7 @@ jobs:
       - name: Build tests
         working-directory: tests/rust
         run: |
-          ./build.py --toolchain=wasm32-wasip3:nightly
+          ./build.py
 
       - name: 'Tar files'
         if: matrix.os == 'ubuntu-latest'

doc/writing-tests.md

@@ -96,9 +96,9 @@ rustup +nightly target add wasm32-wasip2 # for wasip3
 Note that until wasip3 is released, we use the wasip2 toolchain for
 wasip3.
 
-Now you can run `build.py`.  For Rust, run as `./build.py
---toolchain=wasm32-wasip3:nightly`, so as to use the nightly channel
-instead of the default stable, for wasip3.
+Now you can run `build.py`.  For Rust, the build script will
+automatically derive the right channel to use depending on the WASI
+version.
 
 ## Final notes
 

tests/rust/build.py

@@ -15,24 +15,10 @@
                     help="print commands to be executed")
 parser.add_argument("--release", action="store_true",
                     help="build tests in release mode")
-parser.add_argument("--toolchain", action="append",
-                    help="TARGET:TOOLCHAIN, pass +TOOLCHAIN to cargo for TARGET")
-
 args = parser.parse_args()
 if args.dry_run:
     args.verbose = True
 
-TOOLCHAINS={}
-if args.toolchain is not None:
-    for toolchain_arg in args.toolchain:
-        match toolchain_arg.split(':'):
-            case (target, toolchain):
-                TOOLCHAINS[target] = toolchain
-            case arg:
-                print(f"expected --toolchain=TARGET:TOOLCHAIN, got {toolchain_arg}",
-                      file=sys.stderr)
-                sys.exit(1)
-
 CARGO = ['cargo']
 SYSTEMS = ['wasm32']
 VERSIONS = ['wasip1', 'wasip3']
@@ -46,6 +32,14 @@ def compute_build_target(system, version):
         return compute_target(system, 'wasip2')
     return compute_target(system, version)
 
+def compute_channel_for_version(version):
+    # At the time of writing, the nightly channel is
+    # needed in order to make everything work with
+    # WASI p3
+    if version == 'wasip3':
+        return "+nightly"
+    return "+stable"
+
 BASE_DIR = Path(__file__).parent
 
 def run(argv):
@@ -105,9 +99,9 @@ def mkdir_p(path):
         target = compute_target(system, version)
         build_target = compute_build_target(system, version)
         build_mode = "release" if args.release else "debug"
-        toolchain = [f"+{TOOLCHAINS[target]}"] if target in TOOLCHAINS else []
+        channel = compute_channel_for_version(version)
 
-        build_args = CARGO + toolchain + [
+        build_args = CARGO + [channel] + [
             "build",
             f"--manifest-path={BASE_DIR / target / 'Cargo.toml'}",
             f"--target={build_target}"