Update `cargo_bootstrap_repository` interface to match dependency macros (#2630)

This updates the bootstrap repository rule to use the same interface the
dependency macros and crate_universe does:
-
https://github.com/bazelbuild/rules_rust/blob/0.42.1/rust/repositories.bzl#L157-L158
-
https://github.com/bazelbuild/rules_rust/blob/0.42.1/crate_universe/private/crates_repository.bzl#L302-L305

3 files changed, 12 insertions, 19 deletions

diff --git a/cargo/private/cargo_bootstrap.bzl b/cargo/private/cargo_bootstrap.bzl
index 10a0cfaf..beaac8ac 100644
--- a/cargo/private/cargo_bootstrap.bzl
+++ b/cargo/private/cargo_bootstrap.bzl
@@ -177,12 +177,13 @@ def _cargo_bootstrap_repository_impl(repository_ctx):
     # Pretend to Bazel that this rule's input files have been used, so that it will re-run the rule if they change.
     _detect_changes(repository_ctx)
 
-    if repository_ctx.attr.version in ("beta", "nightly"):
-        channel = repository_ctx.attr.version
-        version = repository_ctx.attr.iso_date
+    # Expects something like `1.56.0`, or `nightly/2021-09-08`.
+    version, _, iso_date = repository_ctx.attr.version.partition("/")
+    if iso_date:
+        channel = version
+        version = iso_date
     else:
         channel = "stable"
-        version = repository_ctx.attr.version
 
     host_triple = get_host_triple(repository_ctx)
     cargo_template = repository_ctx.attr.rust_toolchain_cargo_template
@@ -260,9 +261,6 @@ cargo_bootstrap_repository = repository_rule(
                 "Additionally, the platform triple `*` applies to all platforms."
             ),
         ),
-        "iso_date": attr.string(
-            doc = "The iso_date of cargo binary the resolver should use. Note: This can only be set if `version` is `beta` or `nightly`",
-        ),
         "rust_toolchain_cargo_template": attr.string(
             doc = (
                 "The template to use for finding the host `cargo` binary. `{version}` (eg. '1.53.0'), " +
@@ -290,12 +288,9 @@ cargo_bootstrap_repository = repository_rule(
             default = 600,
         ),
         "version": attr.string(
-            doc = "The version of cargo the resolver should use",
+            doc = "The version of Rust the currently registered toolchain is using. Eg. `1.56.0`, or `nightly/2021-09-08`",
             default = rust_common.default_version,
         ),
-        "_cc_toolchain": attr.label(
-            default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
-        ),
     },
 )
 
diff --git a/docs/cargo.md b/docs/cargo.md
index 90e410fa..89050d14 100644
--- a/docs/cargo.md
+++ b/docs/cargo.md
@@ -12,8 +12,8 @@
 
 <pre>
 cargo_bootstrap_repository(<a href="#cargo_bootstrap_repository-name">name</a>, <a href="#cargo_bootstrap_repository-binary">binary</a>, <a href="#cargo_bootstrap_repository-build_mode">build_mode</a>, <a href="#cargo_bootstrap_repository-cargo_lockfile">cargo_lockfile</a>, <a href="#cargo_bootstrap_repository-cargo_toml">cargo_toml</a>, <a href="#cargo_bootstrap_repository-env">env</a>, <a href="#cargo_bootstrap_repository-env_label">env_label</a>,
-                           <a href="#cargo_bootstrap_repository-iso_date">iso_date</a>, <a href="#cargo_bootstrap_repository-repo_mapping">repo_mapping</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_cargo_template">rust_toolchain_cargo_template</a>,
-                           <a href="#cargo_bootstrap_repository-rust_toolchain_rustc_template">rust_toolchain_rustc_template</a>, <a href="#cargo_bootstrap_repository-srcs">srcs</a>, <a href="#cargo_bootstrap_repository-timeout">timeout</a>, <a href="#cargo_bootstrap_repository-version">version</a>)
+                           <a href="#cargo_bootstrap_repository-repo_mapping">repo_mapping</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_cargo_template">rust_toolchain_cargo_template</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_rustc_template">rust_toolchain_rustc_template</a>,
+                           <a href="#cargo_bootstrap_repository-srcs">srcs</a>, <a href="#cargo_bootstrap_repository-timeout">timeout</a>, <a href="#cargo_bootstrap_repository-version">version</a>)
 </pre>
 
 A rule for bootstrapping a Rust binary using [Cargo](https://doc.rust-lang.org/cargo/)
@@ -30,13 +30,12 @@ A rule for bootstrapping a Rust binary using [Cargo](https://doc.rust-lang.org/c
 | <a id="cargo_bootstrap_repository-cargo_toml"></a>cargo_toml |  The path of the crate_universe resolver manifest (<code>Cargo.toml</code> file)   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
 | <a id="cargo_bootstrap_repository-env"></a>env |  A mapping of platform triple to a set of environment variables. See [cargo_env](#cargo_env) for usage details. Additionally, the platform triple <code>*</code> applies to all platforms.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="cargo_bootstrap_repository-env_label"></a>env_label |  A mapping of platform triple to a set of environment variables. This attribute differs from <code>env</code> in that all variables passed here must be fully qualified labels of files. See [cargo_env](#cargo_env) for usage details. Additionally, the platform triple <code>*</code> applies to all platforms.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
-| <a id="cargo_bootstrap_repository-iso_date"></a>iso_date |  The iso_date of cargo binary the resolver should use. Note: This can only be set if <code>version</code> is <code>beta</code> or <code>nightly</code>   | String | optional | <code>""</code> |
 | <a id="cargo_bootstrap_repository-repo_mapping"></a>repo_mapping |  A dictionary from local repository name to global repository name. This allows controls over workspace dependency resolution for dependencies of this repository.&lt;p&gt;For example, an entry <code>"@foo": "@bar"</code> declares that, for any time this repository depends on <code>@foo</code> (such as a dependency on <code>@foo//some:target</code>, it should actually resolve that dependency within globally-declared <code>@bar</code> (<code>@bar//some:target</code>).   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | required |  |
 | <a id="cargo_bootstrap_repository-rust_toolchain_cargo_template"></a>rust_toolchain_cargo_template |  The template to use for finding the host <code>cargo</code> binary. <code>{version}</code> (eg. '1.53.0'), <code>{triple}</code> (eg. 'x86_64-unknown-linux-gnu'), <code>{arch}</code> (eg. 'aarch64'), <code>{vendor}</code> (eg. 'unknown'), <code>{system}</code> (eg. 'darwin'), <code>{channel}</code> (eg. 'stable'), and <code>{tool}</code> (eg. 'rustc.exe') will be replaced in the string if present.   | String | optional | <code>"@rust_{system}_{arch}__{triple}__{channel}_tools//:bin/{tool}"</code> |
 | <a id="cargo_bootstrap_repository-rust_toolchain_rustc_template"></a>rust_toolchain_rustc_template |  The template to use for finding the host <code>rustc</code> binary. <code>{version}</code> (eg. '1.53.0'), <code>{triple}</code> (eg. 'x86_64-unknown-linux-gnu'), <code>{arch}</code> (eg. 'aarch64'), <code>{vendor}</code> (eg. 'unknown'), <code>{system}</code> (eg. 'darwin'), <code>{channel}</code> (eg. 'stable'), and <code>{tool}</code> (eg. 'rustc.exe') will be replaced in the string if present.   | String | optional | <code>"@rust_{system}_{arch}__{triple}__{channel}_tools//:bin/{tool}"</code> |
 | <a id="cargo_bootstrap_repository-srcs"></a>srcs |  Souce files of the crate to build. Passing source files here can be used to trigger rebuilds when changes are made   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional | <code>[]</code> |
 | <a id="cargo_bootstrap_repository-timeout"></a>timeout |  Maximum duration of the Cargo build command in seconds   | Integer | optional | <code>600</code> |
-| <a id="cargo_bootstrap_repository-version"></a>version |  The version of cargo the resolver should use   | String | optional | <code>"1.77.2"</code> |
+| <a id="cargo_bootstrap_repository-version"></a>version |  The version of Rust the currently registered toolchain is using. Eg. <code>1.56.0</code>, or <code>nightly/2021-09-08</code>   | String | optional | <code>"1.77.2"</code> |
 
 
 <a id="cargo_dep_env"></a>
diff --git a/docs/flatten.md b/docs/flatten.md
index 6a8d7a50..c567f2af 100644
--- a/docs/flatten.md
+++ b/docs/flatten.md
@@ -86,8 +86,8 @@ Control whether to print clippy output or store it to a file, using the configur
 
 <pre>
 cargo_bootstrap_repository(<a href="#cargo_bootstrap_repository-name">name</a>, <a href="#cargo_bootstrap_repository-binary">binary</a>, <a href="#cargo_bootstrap_repository-build_mode">build_mode</a>, <a href="#cargo_bootstrap_repository-cargo_lockfile">cargo_lockfile</a>, <a href="#cargo_bootstrap_repository-cargo_toml">cargo_toml</a>, <a href="#cargo_bootstrap_repository-env">env</a>, <a href="#cargo_bootstrap_repository-env_label">env_label</a>,
-                           <a href="#cargo_bootstrap_repository-iso_date">iso_date</a>, <a href="#cargo_bootstrap_repository-repo_mapping">repo_mapping</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_cargo_template">rust_toolchain_cargo_template</a>,
-                           <a href="#cargo_bootstrap_repository-rust_toolchain_rustc_template">rust_toolchain_rustc_template</a>, <a href="#cargo_bootstrap_repository-srcs">srcs</a>, <a href="#cargo_bootstrap_repository-timeout">timeout</a>, <a href="#cargo_bootstrap_repository-version">version</a>)
+                           <a href="#cargo_bootstrap_repository-repo_mapping">repo_mapping</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_cargo_template">rust_toolchain_cargo_template</a>, <a href="#cargo_bootstrap_repository-rust_toolchain_rustc_template">rust_toolchain_rustc_template</a>,
+                           <a href="#cargo_bootstrap_repository-srcs">srcs</a>, <a href="#cargo_bootstrap_repository-timeout">timeout</a>, <a href="#cargo_bootstrap_repository-version">version</a>)
 </pre>
 
 A rule for bootstrapping a Rust binary using [Cargo](https://doc.rust-lang.org/cargo/)
@@ -104,13 +104,12 @@ A rule for bootstrapping a Rust binary using [Cargo](https://doc.rust-lang.org/c
 | <a id="cargo_bootstrap_repository-cargo_toml"></a>cargo_toml |  The path of the crate_universe resolver manifest (<code>Cargo.toml</code> file)   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
 | <a id="cargo_bootstrap_repository-env"></a>env |  A mapping of platform triple to a set of environment variables. See [cargo_env](#cargo_env) for usage details. Additionally, the platform triple <code>*</code> applies to all platforms.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="cargo_bootstrap_repository-env_label"></a>env_label |  A mapping of platform triple to a set of environment variables. This attribute differs from <code>env</code> in that all variables passed here must be fully qualified labels of files. See [cargo_env](#cargo_env) for usage details. Additionally, the platform triple <code>*</code> applies to all platforms.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
-| <a id="cargo_bootstrap_repository-iso_date"></a>iso_date |  The iso_date of cargo binary the resolver should use. Note: This can only be set if <code>version</code> is <code>beta</code> or <code>nightly</code>   | String | optional | <code>""</code> |
 | <a id="cargo_bootstrap_repository-repo_mapping"></a>repo_mapping |  A dictionary from local repository name to global repository name. This allows controls over workspace dependency resolution for dependencies of this repository.&lt;p&gt;For example, an entry <code>"@foo": "@bar"</code> declares that, for any time this repository depends on <code>@foo</code> (such as a dependency on <code>@foo//some:target</code>, it should actually resolve that dependency within globally-declared <code>@bar</code> (<code>@bar//some:target</code>).   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | required |  |
 | <a id="cargo_bootstrap_repository-rust_toolchain_cargo_template"></a>rust_toolchain_cargo_template |  The template to use for finding the host <code>cargo</code> binary. <code>{version}</code> (eg. '1.53.0'), <code>{triple}</code> (eg. 'x86_64-unknown-linux-gnu'), <code>{arch}</code> (eg. 'aarch64'), <code>{vendor}</code> (eg. 'unknown'), <code>{system}</code> (eg. 'darwin'), <code>{channel}</code> (eg. 'stable'), and <code>{tool}</code> (eg. 'rustc.exe') will be replaced in the string if present.   | String | optional | <code>"@rust_{system}_{arch}__{triple}__{channel}_tools//:bin/{tool}"</code> |
 | <a id="cargo_bootstrap_repository-rust_toolchain_rustc_template"></a>rust_toolchain_rustc_template |  The template to use for finding the host <code>rustc</code> binary. <code>{version}</code> (eg. '1.53.0'), <code>{triple}</code> (eg. 'x86_64-unknown-linux-gnu'), <code>{arch}</code> (eg. 'aarch64'), <code>{vendor}</code> (eg. 'unknown'), <code>{system}</code> (eg. 'darwin'), <code>{channel}</code> (eg. 'stable'), and <code>{tool}</code> (eg. 'rustc.exe') will be replaced in the string if present.   | String | optional | <code>"@rust_{system}_{arch}__{triple}__{channel}_tools//:bin/{tool}"</code> |
 | <a id="cargo_bootstrap_repository-srcs"></a>srcs |  Souce files of the crate to build. Passing source files here can be used to trigger rebuilds when changes are made   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional | <code>[]</code> |
 | <a id="cargo_bootstrap_repository-timeout"></a>timeout |  Maximum duration of the Cargo build command in seconds   | Integer | optional | <code>600</code> |
-| <a id="cargo_bootstrap_repository-version"></a>version |  The version of cargo the resolver should use   | String | optional | <code>"1.77.2"</code> |
+| <a id="cargo_bootstrap_repository-version"></a>version |  The version of Rust the currently registered toolchain is using. Eg. <code>1.56.0</code>, or <code>nightly/2021-09-08</code>   | String | optional | <code>"1.77.2"</code> |
 
 
 <a id="cargo_dep_env"></a>