Update README, minor protoc toolchain cleanups

Fixes a broken `single_version_override` link in the README. Added info
explicitly indicating that `repo_mapping` and other mechanisms used to
translate `@rules_scala_config` also apply to translating
`@rules_scala`.

Slightly touches up `protoc_toolchain.bzl` and
`update_protoc_integrity.py.

README.md

@@ -166,7 +166,12 @@ v6.x:
 
 - __`rules_scala` no longer requires the `io_bazel_rules_scala` repository
     name__ unless your `BUILD` files or those of your dependencies require it
-    (bazelbuild/rules_scala#1696).
+    (bazelbuild/rules_scala#1696). You can use the `repo_mapping` attribute of
+    `http_archive`, or equivalent Bzlmod mechanisms, to translate `@rules_scala`
+    to `@io_bazel_rules_scala` for dependencies. The
+    ['@io_bazel_rules_scala_config' is now '@rules_scala_config'](#map) section
+    below describes these options in detail. (That section is about
+    `@rules_scala_config`, but the same mechanisms apply.)
 
 - __`rules_scala` v7.0.0 introduces a new `scala_toolchains()` API that is
     very different from `rules_scala` 6__. For details on what's changed, see
@@ -237,6 +242,7 @@ which also requires that the patch be a regular file in your own repo. In other
 words, neither `@rules_scala//protoc:0001-protobuf-19679-rm-protoc-dep.patch`
 nor an [`alias`][] to it will work.
 
+[`single_version_override`]: https://bazel.build/rules/lib/globals/module#single_version_override
 [`alias`]: https://bazel.build/reference/be/general#alias
 
 Assuming you've copied the patch to a file called `protobuf.patch` in the root
@@ -667,7 +673,7 @@ register_toolchains(
 )
 ```
 
-### `@io_bazel_rules_scala_config` is now `@rules_scala_config`
+### <a id="map"></a>`@io_bazel_rules_scala_config` is now `@rules_scala_config`
 
 Since `@io_bazel_rules_scala` is no longer hardcoded in `rules_scala` internals,
 we've shortened `@io_bazel_rules_scala_config` to `@rules_scala_config`. This
@@ -676,7 +682,16 @@ shouldn't affect most users, but it may break some builds using
 ./docs/cross-compilation.md).
 
 If you can't fix uses of `@io_bazel_rules_scala_config` in your own project
-immediately, you can remap `@rules_scala_config` via [`use_repo()`]:
+immediately, or have dependencies that need it, there are options.
+Use one of the following mechanisms to override it with `@rules_scala_config`.
+
+The same mechanisms also apply if you need to translate `@rules_scala` to
+`@io_bazel_rules_scala` for your dependencies.
+
+#### Bzlmod
+
+You can remap `@rules_scala_config` via [`use_repo()`] if you need it in your
+own project:
 
 [`use_repo()`]: https://bazel.build/rules/lib/globals/module#use_repo
 
@@ -689,11 +704,6 @@ scala_config = use_extension(
 use_repo(scala_config, io_bazel_rules_scala_config = "rules_scala_config")
 ```
 
-If any of your dependencies still require `@io_bazel_rules_scala_config`, use
-one of the following mechanisms to override it with `@rules_scala_config`:
-
-#### Bzlmod
-
 For [`bazel_dep()`][] dependencies, use [`override_repo()`][] to
 override `@io_bazel_rules_scala_config` with `@rules_scala_config`:
 

protoc/private/protoc_toolchain.bzl

@@ -28,8 +28,6 @@ def _platform_build(platform):
         )
     return protoc_build
 
-_PROTOC_BUILD_ENTRY_TEMPLATE = """    "{platform}": [\n{specs}\n    ],"""
-
 def _download_build(repository_ctx, package, platform, protoc_build):
     repository_ctx.download_and_extract(
         url = PROTOC_DOWNLOAD_URL.format(
@@ -41,7 +39,7 @@ def _download_build(repository_ctx, package, platform, protoc_build):
     )
 
 def _emit_platform_entry(platform, protoc_build):
-    return _PROTOC_BUILD_ENTRY_TEMPLATE.format(
+    return '    "{platform}": [\n{specs}\n    ],'.format(
         platform = platform,
         specs = "\n".join([
             '        "%s",' % s

scripts/update_protoc_integrity.py

@@ -116,14 +116,10 @@ def get_protoc_integrity(platform, version):
     Raises:
         `UpdateProtocIntegrityError` if downloading or checksumming fails
     """
-    try:
-        url = PROTOC_DOWNLOAD_URL.format(
-          version = version,
-          platform = platform
-        )
-        print(f'Updating protoc {version} for {platform}:')
-        print(f'  {url}')
+    url = PROTOC_DOWNLOAD_URL.format(version = version, platform = platform)
+    print(f'Updating protoc {version} for {platform}:\n  {url}')
 
+    try:
         with urllib.request.urlopen(url) as data:
             body = data.read()