rustc wrapper respects CARGO_BUILD_TARGET

.gitignore

@@ -1 +1,2 @@
 /MutableArtifacts.toml
+Manifest.toml

src/Runner.jl

@@ -792,14 +792,17 @@ function generate_compiler_wrappers!(platform::AbstractPlatform; bin_path::Abstr
     end
     function rustc(io::IO, p::AbstractPlatform)
         extra_cmds = """
+        # Default to this platform's target unless overridden in the environment
+        rust_target="\${CARGO_BUILD_TARGET:-$(map_rust_target(p))}"
+
         if [[ " \${ARGS[@]} " == *'--target'* ]]; then
-            if ! [[ " \${ARGS[@]} " =~ --target(=| )$(map_rust_target(p)) ]]; then
-                echo "Attempting to invoke targeted 'rustc' wrapper with a different target! (Expected $(map_rust_target(p)))" >&2
+            if ! [[ " \${ARGS[@]} " =~ --target(=| )\${rust_target} ]]; then
+                echo "Attempting to invoke targeted 'rustc' wrapper with a different target! (Expected \${rust_target} from CARGO_BUILD_TARGET or default)" >&2
                 echo "args: \${ARGS[@]}" >&2
                 exit 1
             fi
         else
-            PRE_FLAGS+=( '--target=$(map_rust_target(p))' )
+            PRE_FLAGS+=( "--target=\${rust_target}" )
         fi
         """
         wrapper(io, "/opt/$(host_target)/bin/rustc"; flags=rust_flags!(p), allow_ccache=false, extra_cmds=extra_cmds)

test/rootfs.jl

@@ -310,7 +310,9 @@ end
                 @test occursin("-L/opt/$(triplet(platform))/$(triplet(platform))/lib", clang)
                 # Other compilers
                 @test occursin("GOOS=\"freebsd\"", read(joinpath(platform_bin_dir, "go"), String))
-                @test occursin("--target=x86_64-unknown-freebsd", read(joinpath(platform_bin_dir, "rustc"), String))
+                rustc_script = read(joinpath(platform_bin_dir, "rustc"), String)
+                @test occursin("rust_target=\"\${CARGO_BUILD_TARGET:-x86_64-unknown-freebsd}\"", rustc_script)
+                @test occursin("--target=\${rust_target}", rustc_script)
             end
         end
         platform = Platform("x86_64", "linux"; libc="glibc", cxxstring_abi="cxx11")