[Runners] JIT-generate Cargo config file

This will replace the file we currently hard-code in the Rust compiler shard.

src/BuildToolchains.jl

@@ -214,8 +214,8 @@ function toolchain_file(bt::Meson, p::AbstractPlatform, envs::Dict{String,String
     """
 end
 
-function generate_toolchain_files!(platform::AbstractPlatform, envs::Dict{String,String};
-                                   toolchains_path::AbstractString,
+function generate_toolchain_files!(platform::AbstractPlatform, envs::Dict{String,String},
+                                   toolchains_path::AbstractString;
                                    host_platform::AbstractPlatform = default_host_platform,
                                    )
 
@@ -253,3 +253,29 @@ function generate_toolchain_files!(platform::AbstractPlatform, envs::Dict{String
         end
     end
 end
+
+function cargo_config_file!(dir::AbstractString)
+    # Generate "${CARGO_HOME}/config.toml" file for Cargo where we give it the
+    # linkers for all our targets
+    open(joinpath(dir, "config.toml"), "w") do io
+        write(io, """
+        # Configuration file for `cargo`
+        """)
+        for platform in supported_platforms()
+            # Use `aatriplet` for the linker to match how the wrappers are
+            # written in
+            # https://github.com/JuliaPackaging/BinaryBuilderBase.jl/blob/30d056ef68f81dca9cb91ededcce6b68c6466b37/src/Runner.jl#L599.
+            write(io, """
+            [target.$(map_rust_target(platform))]
+            linker = "$(aatriplet(platform))-gcc"
+            """)
+            if platforms_match(platform, Platform("aarch64", "linux"; libc="musl"))
+                # Work around bug for this platform:
+                # https://github.com/rust-lang/rust/issues/46651#issuecomment-433611633
+                write(io, """
+                rustflags = ["-C", "link-arg=-lgcc"]
+                """)
+            end
+        end
+    end
+end

src/DockerRunner.jl

@@ -93,9 +93,19 @@ function DockerRunner(workspace_root::String;
     push!(workspaces, compiler_wrapper_path => "/opt/bin")
 
     # Generate CMake and Meson files
-    generate_toolchain_files!(platform, envs; toolchains_path=toolchains_path)
+    generate_toolchain_files!(platform, envs, toolchains_path)
     push!(workspaces, toolchains_path => "/opt/toolchains")
 
+    # Generate directory where to write Cargo config files
+    compilers = collect(extract_kwargs(kwargs, (:compilers,)))
+    if isone(length(compilers)) && :rust in compilers[1].second
+        cargo_dir = mktempdir()
+        cargo_config_file!(cargo_dir)
+        # Add to the list of mappings a subdirectory of ${CARGO_HOME}, whose content
+        # will be put in ${CARGO_HOME}.
+        push!(workspaces, cargo_dir => envs["CARGO_HOME"] * "/" * randstring())
+    end
+
     # the workspace_root is always a workspace, and we always mount it first
     insert!(workspaces, 1, workspace_root => "/workspace")
 

src/UserNSRunner.jl

@@ -48,9 +48,19 @@ function UserNSRunner(workspace_root::String;
     push!(workspaces, compiler_wrapper_path => "/opt/bin")
 
     # Generate CMake and Meson files
-    generate_toolchain_files!(platform, envs; toolchains_path=toolchains_path)
+    generate_toolchain_files!(platform, envs, toolchains_path)
     push!(workspaces, toolchains_path => "/opt/toolchains")
 
+    # Generate directory where to write Cargo config files
+    compilers = collect(extract_kwargs(kwargs, (:compilers,)))
+    if isone(length(compilers)) && :rust in compilers[1].second
+        cargo_dir = mktempdir()
+        cargo_config_file!(cargo_dir)
+        # Add to the list of mappings a subdirectory of ${CARGO_HOME}, whose content
+        # will be put in ${CARGO_HOME}.
+        push!(mappings, cargo_dir => envs["CARGO_HOME"] * "/" * randstring())
+    end
+
     # the workspace_root is always a workspace, and we always mount it first
     insert!(workspaces, 1, workspace_root => "/workspace")