Allow specifying exec and target compatibility constraints (#1971)

Extra target triples may only be appropriate for specific platforms
(e.g. if you register a toolchain with the exec_triple
`x86_64-unknown-linux-gnu` with an extra target triple of
`x86_64-unknown-linux-musl`, you may want differing
`target_compatible_with` values for each of those two target triples.

This allows for specifying explicit `exec_compatible_with` lists per
toolchain (which was already supported by `rust_toolchain_repository`
just not proxied by `rust_repository_set`), and explicit
`target_compatible_with` lists, both for the default triple and for
extra ones.

I'm not 100% sure on our pre-existing assumption that every toolchain
supports compiling targeting its own exec platform, i.e. the
'`[exec_triple]`' part of https://github.com/bazelbuild/rules_rust/blob/937e63399b111a6d7ee53b187e4d113300b089e9/rust/repositories.bzl#L845
but it _does_ generally hold, and supplying a way of removing that
default assumption is definitely a separate PR for another day if it
becomes relevant to anyone.

Author: illicitonion

docs/flatten.md

@@ -1851,7 +1851,7 @@ rust_repositories(<a href="#rust_repositories-kwargs">kwargs</a>)
 rust_repository_set(<a href="#rust_repository_set-name">name</a>, <a href="#rust_repository_set-exec_triple">exec_triple</a>, <a href="#rust_repository_set-target_settings">target_settings</a>, <a href="#rust_repository_set-version">version</a>, <a href="#rust_repository_set-versions">versions</a>, <a href="#rust_repository_set-allocator_library">allocator_library</a>,
                     <a href="#rust_repository_set-global_allocator_library">global_allocator_library</a>, <a href="#rust_repository_set-extra_target_triples">extra_target_triples</a>, <a href="#rust_repository_set-iso_date">iso_date</a>, <a href="#rust_repository_set-rustfmt_version">rustfmt_version</a>,
                     <a href="#rust_repository_set-edition">edition</a>, <a href="#rust_repository_set-dev_components">dev_components</a>, <a href="#rust_repository_set-extra_rustc_flags">extra_rustc_flags</a>, <a href="#rust_repository_set-extra_exec_rustc_flags">extra_exec_rustc_flags</a>, <a href="#rust_repository_set-sha256s">sha256s</a>, <a href="#rust_repository_set-urls">urls</a>,
-                    <a href="#rust_repository_set-auth">auth</a>, <a href="#rust_repository_set-register_toolchain">register_toolchain</a>)
+                    <a href="#rust_repository_set-auth">auth</a>, <a href="#rust_repository_set-register_toolchain">register_toolchain</a>, <a href="#rust_repository_set-exec_compatible_with">exec_compatible_with</a>, <a href="#rust_repository_set-default_target_compatible_with">default_target_compatible_with</a>)
 </pre>
 
 Assembles a remote repository for the given toolchain params, produces a proxy repository     to contain the toolchain declaration, and registers the toolchains.
@@ -1868,7 +1868,7 @@ Assembles a remote repository for the given toolchain params, produces a proxy r
 | <a id="rust_repository_set-versions"></a>versions |  A list of toolchain versions to download. This paramter only accepts one versions per channel. E.g. <code>["1.65.0", "nightly/2022-11-02", "beta/2020-12-30"]</code>.   |  `[]` |
 | <a id="rust_repository_set-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   |  `None` |
 | <a id="rust_repository_set-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions a global allocator is used with cc_common.link.   |  `None` |
-| <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support.   |  `[]` |
+| <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support. If a map, values should be (optional) target_compatible_with lists for that particular target triple.   |  `{}` |
 | <a id="rust_repository_set-iso_date"></a>iso_date |  The date of the tool.   |  `None` |
 | <a id="rust_repository_set-rustfmt_version"></a>rustfmt_version |  The version of rustfmt to be associated with the toolchain.   |  `None` |
 | <a id="rust_repository_set-edition"></a>edition |  The rust edition to be used by default (2015, 2018, or 2021). If absent, every rule is required to specify its <code>edition</code> attribute.   |  `None` |
@@ -1879,6 +1879,8 @@ Assembles a remote repository for the given toolchain params, produces a proxy r
 | <a id="rust_repository_set-urls"></a>urls |  A list of mirror urls containing the tools from the Rust-lang static file server. These must contain the '{}' used to substitute the tool being fetched (using .format).   |  `["https://static.rust-lang.org/dist/{}.tar.gz"]` |
 | <a id="rust_repository_set-auth"></a>auth |  Auth object compatible with repository_ctx.download to use when downloading files. See [repository_ctx.download](https://docs.bazel.build/versions/main/skylark/lib/repository_ctx.html#download) for more details.   |  `None` |
 | <a id="rust_repository_set-register_toolchain"></a>register_toolchain |  If True, the generated <code>rust_toolchain</code> target will become a registered toolchain.   |  `True` |
+| <a id="rust_repository_set-exec_compatible_with"></a>exec_compatible_with |  A list of constraints for the execution platform for this toolchain.   |  `None` |
+| <a id="rust_repository_set-default_target_compatible_with"></a>default_target_compatible_with |  A list of constraints for the target platform for this toolchain when the exec platform is the same as the target platform.   |  `None` |
 
 
 <a id="rust_test_suite"></a>

docs/rust_repositories.md

@@ -303,7 +303,7 @@ rust_repositories(<a href="#rust_repositories-kwargs">kwargs</a>)
 rust_repository_set(<a href="#rust_repository_set-name">name</a>, <a href="#rust_repository_set-exec_triple">exec_triple</a>, <a href="#rust_repository_set-target_settings">target_settings</a>, <a href="#rust_repository_set-version">version</a>, <a href="#rust_repository_set-versions">versions</a>, <a href="#rust_repository_set-allocator_library">allocator_library</a>,
                     <a href="#rust_repository_set-global_allocator_library">global_allocator_library</a>, <a href="#rust_repository_set-extra_target_triples">extra_target_triples</a>, <a href="#rust_repository_set-iso_date">iso_date</a>, <a href="#rust_repository_set-rustfmt_version">rustfmt_version</a>,
                     <a href="#rust_repository_set-edition">edition</a>, <a href="#rust_repository_set-dev_components">dev_components</a>, <a href="#rust_repository_set-extra_rustc_flags">extra_rustc_flags</a>, <a href="#rust_repository_set-extra_exec_rustc_flags">extra_exec_rustc_flags</a>, <a href="#rust_repository_set-sha256s">sha256s</a>, <a href="#rust_repository_set-urls">urls</a>,
-                    <a href="#rust_repository_set-auth">auth</a>, <a href="#rust_repository_set-register_toolchain">register_toolchain</a>)
+                    <a href="#rust_repository_set-auth">auth</a>, <a href="#rust_repository_set-register_toolchain">register_toolchain</a>, <a href="#rust_repository_set-exec_compatible_with">exec_compatible_with</a>, <a href="#rust_repository_set-default_target_compatible_with">default_target_compatible_with</a>)
 </pre>
 
 Assembles a remote repository for the given toolchain params, produces a proxy repository     to contain the toolchain declaration, and registers the toolchains.
@@ -320,7 +320,7 @@ Assembles a remote repository for the given toolchain params, produces a proxy r
 | <a id="rust_repository_set-versions"></a>versions |  A list of toolchain versions to download. This paramter only accepts one versions per channel. E.g. <code>["1.65.0", "nightly/2022-11-02", "beta/2020-12-30"]</code>.   |  `[]` |
 | <a id="rust_repository_set-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   |  `None` |
 | <a id="rust_repository_set-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions a global allocator is used with cc_common.link.   |  `None` |
-| <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support.   |  `[]` |
+| <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support. If a map, values should be (optional) target_compatible_with lists for that particular target triple.   |  `{}` |
 | <a id="rust_repository_set-iso_date"></a>iso_date |  The date of the tool.   |  `None` |
 | <a id="rust_repository_set-rustfmt_version"></a>rustfmt_version |  The version of rustfmt to be associated with the toolchain.   |  `None` |
 | <a id="rust_repository_set-edition"></a>edition |  The rust edition to be used by default (2015, 2018, or 2021). If absent, every rule is required to specify its <code>edition</code> attribute.   |  `None` |
@@ -331,6 +331,8 @@ Assembles a remote repository for the given toolchain params, produces a proxy r
 | <a id="rust_repository_set-urls"></a>urls |  A list of mirror urls containing the tools from the Rust-lang static file server. These must contain the '{}' used to substitute the tool being fetched (using .format).   |  `["https://static.rust-lang.org/dist/{}.tar.gz"]` |
 | <a id="rust_repository_set-auth"></a>auth |  Auth object compatible with repository_ctx.download to use when downloading files. See [repository_ctx.download](https://docs.bazel.build/versions/main/skylark/lib/repository_ctx.html#download) for more details.   |  `None` |
 | <a id="rust_repository_set-register_toolchain"></a>register_toolchain |  If True, the generated <code>rust_toolchain</code> target will become a registered toolchain.   |  `True` |
+| <a id="rust_repository_set-exec_compatible_with"></a>exec_compatible_with |  A list of constraints for the execution platform for this toolchain.   |  `None` |
+| <a id="rust_repository_set-default_target_compatible_with"></a>default_target_compatible_with |  A list of constraints for the target platform for this toolchain when the exec platform is the same as the target platform.   |  `None` |
 
 
 <a id="rust_toolchain_repository"></a>

rust/repositories.bzl

@@ -881,7 +881,7 @@ def rust_repository_set(
         versions = [],
         allocator_library = None,
         global_allocator_library = None,
-        extra_target_triples = [],
+        extra_target_triples = {},
         iso_date = None,
         rustfmt_version = None,
         edition = None,
@@ -891,7 +891,9 @@ def rust_repository_set(
         sha256s = None,
         urls = DEFAULT_STATIC_RUST_URL_TEMPLATES,
         auth = None,
-        register_toolchain = True):
+        register_toolchain = True,
+        exec_compatible_with = None,
+        default_target_compatible_with = None):
     """Assembles a remote repository for the given toolchain params, produces a proxy repository \
     to contain the toolchain declaration, and registers the toolchains.
 
@@ -905,8 +907,8 @@ def rust_repository_set(
         allocator_library (str, optional): Target that provides allocator functions when rust_library targets are
             embedded in a cc_binary.
         global_allocator_library (str, optional): Target that provides allocator functions a global allocator is used with cc_common.link.
-        extra_target_triples (list, optional): Additional rust-style targets that this set of
-            toolchains should support.
+        extra_target_triples (list or map, optional): Additional rust-style targets that this set of
+            toolchains should support. If a map, values should be (optional) target_compatible_with lists for that particular target triple.
         iso_date (str, optional): The date of the tool.
         rustfmt_version (str, optional):  The version of rustfmt to be associated with the
             toolchain.
@@ -923,6 +925,8 @@ def rust_repository_set(
         auth (dict): Auth object compatible with repository_ctx.download to use when downloading files.
             See [repository_ctx.download](https://docs.bazel.build/versions/main/skylark/lib/repository_ctx.html#download) for more details.
         register_toolchain (bool): If True, the generated `rust_toolchain` target will become a registered toolchain.
+        exec_compatible_with (list, optional): A list of constraints for the execution platform for this toolchain.
+        default_target_compatible_with (list, optional): A list of constraints for the target platform for this toolchain when the exec platform is the same as the target platform.
     """
 
     if version and versions:
@@ -942,8 +946,20 @@ def rust_repository_set(
     if version and not versions:
         versions = [version]
 
+    # extra_target_triples may be a dict or list - make a list we can pass to _get_toolchain_repositories
+    extra_target_triples_list = []
+    for extra_target_triple in extra_target_triples:
+        extra_target_triples_list.append(extra_target_triple)
+
     all_toolchain_names = []
-    for toolchain in _get_toolchain_repositories(name, exec_triple, extra_target_triples, versions, iso_date):
+    for toolchain in _get_toolchain_repositories(name, exec_triple, extra_target_triples_list, versions, iso_date):
+        target_compatible_with = None
+        if toolchain.target_triple == exec_triple:
+            # The exec triple implicitly gets a toolchain with itself as a target - use default_target_compatible_with for it
+            target_compatible_with = default_target_compatible_with
+        elif type(extra_target_triples) == "dict":
+            target_compatible_with = extra_target_triples.get(toolchain.target_triple)
+
         all_toolchain_names.append(rust_toolchain_repository(
             name = toolchain.name,
             allocator_library = allocator_library,
@@ -962,6 +978,8 @@ def rust_repository_set(
             target_triple = toolchain.target_triple,
             urls = urls,
             version = toolchain.channel.version,
+            exec_compatible_with = exec_compatible_with,
+            target_compatible_with = target_compatible_with,
         ))
 
     # This repository exists to allow `rust_repository_set` to work with the `maybe` wrapper.