Remove DEFAULT_RUST_EDITION (#1256)

* Recognize `edition = "required"` idiom

* Remove DEFAULT_RUST_EDITION

Author: dtolnay

docs/flatten.md

@@ -787,7 +787,7 @@ See @rules_rust//proto:BUILD for examples of defining the toolchain.
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_proto_toolchain-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
-| <a id="rust_proto_toolchain-edition"></a>edition |  The edition used by the generated rust source.   | String | optional | "2018" |
+| <a id="rust_proto_toolchain-edition"></a>edition |  The edition used by the generated rust source.   | String | optional | "" |
 | <a id="rust_proto_toolchain-grpc_compile_deps"></a>grpc_compile_deps |  The crates the generated grpc libraries depends on.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [Label("//proto/raze:protobuf"), Label("//proto/raze:grpc"), Label("//proto/raze:tls_api"), Label("//proto/raze:tls_api_stub")] |
 | <a id="rust_proto_toolchain-grpc_plugin"></a>grpc_plugin |  The location of the Rust protobuf compiler plugin to generate rust gRPC stubs.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | //proto:protoc_gen_rust_grpc |
 | <a id="rust_proto_toolchain-proto_compile_deps"></a>proto_compile_deps |  The crates the generated protobuf libraries depends on.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [Label("//proto/raze:protobuf")] |
@@ -1120,7 +1120,7 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
 | <a id="rust_toolchain-cargo"></a>cargo |  The location of the <code>cargo</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-clippy_driver"></a>clippy_driver |  The location of the <code>clippy-driver</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-debug_info"></a>debug_info |  Rustc debug info levels per opt level   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {"dbg": "2", "fastbuild": "0", "opt": "0"} |
-| <a id="rust_toolchain-default_edition"></a>default_edition |  The edition to use for rust_* rules that don't specify an edition.   | String | optional | "2018" |
+| <a id="rust_toolchain-default_edition"></a>default_edition |  The edition to use for rust_* rules that don't specify an edition. If absent, every rule is required to specify its <code>edition</code> attribute.   | String | optional | "" |
 | <a id="rust_toolchain-dylib_ext"></a>dylib_ext |  The extension for dynamic libraries created from rustc.   | String | required |  |
 | <a id="rust_toolchain-exec_triple"></a>exec_triple |  The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations   | String | required |  |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
@@ -1161,7 +1161,7 @@ A given instance of this rule should be accompanied by a rust_toolchain_reposito
 | <a id="rust_toolchain_repository-name"></a>name |  A unique name for this repository.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
 | <a id="rust_toolchain_repository-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.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_toolchain_repository-dev_components"></a>dev_components |  Whether to download the rustc-dev components (defaults to False). Requires version to be "nightly".   | Boolean | optional | False |
-| <a id="rust_toolchain_repository-edition"></a>edition |  The rust edition to be used by default.   | String | optional | "2018" |
+| <a id="rust_toolchain_repository-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.   | String | optional | "" |
 | <a id="rust_toolchain_repository-exec_triple"></a>exec_triple |  The Rust-style target that this compiler runs on   | String | required |  |
 | <a id="rust_toolchain_repository-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support.   | List of strings | optional | [] |
 | <a id="rust_toolchain_repository-include_rustc_srcs"></a>include_rustc_srcs |  Whether to download and unpack the rustc source files. These are very large, and slow to unpack, but are required to support rust analyzer. An environment variable <code>RULES_RUST_TOOLCHAIN_INCLUDE_RUSTC_SRCS</code> can also be used to control this attribute. This variable will take precedence over the hard coded attribute. Setting it to <code>true</code> to activates this attribute where all other values deactivate it.   | Boolean | optional | False |
@@ -1635,7 +1635,7 @@ N.B. A "proxy repository" is needed to allow for registering the toolchain (with
 | <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support. Defaults to [].   |  <code>[]</code> |
 | <a id="rust_repository_set-iso_date"></a>iso_date |  The date of the tool. Defaults to None.   |  <code>None</code> |
 | <a id="rust_repository_set-rustfmt_version"></a>rustfmt_version |  The version of rustfmt to be associated with the toolchain. Defaults to None.   |  <code>None</code> |
-| <a id="rust_repository_set-edition"></a>edition |  The rust edition to be used by default (2015, 2018 (if None), or 2021).   |  <code>None</code> |
+| <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.   |  <code>None</code> |
 | <a id="rust_repository_set-dev_components"></a>dev_components |  Whether to download the rustc-dev components. Requires version to be "nightly". Defaults to False.   |  <code>False</code> |
 | <a id="rust_repository_set-sha256s"></a>sha256s |  A dict associating tool subdirectories to sha256 hashes. See [rust_repositories](#rust_repositories) for more details.   |  <code>None</code> |
 | <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). Defaults to ['https://static.rust-lang.org/dist/{}.tar.gz']   |  <code>["https://static.rust-lang.org/dist/{}.tar.gz"]</code> |

docs/rust_proto.md

@@ -252,7 +252,7 @@ See @rules_rust//proto:BUILD for examples of defining the toolchain.
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_proto_toolchain-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
-| <a id="rust_proto_toolchain-edition"></a>edition |  The edition used by the generated rust source.   | String | optional | "2018" |
+| <a id="rust_proto_toolchain-edition"></a>edition |  The edition used by the generated rust source.   | String | optional | "" |
 | <a id="rust_proto_toolchain-grpc_compile_deps"></a>grpc_compile_deps |  The crates the generated grpc libraries depends on.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [Label("//proto/raze:protobuf"), Label("//proto/raze:grpc"), Label("//proto/raze:tls_api"), Label("//proto/raze:tls_api_stub")] |
 | <a id="rust_proto_toolchain-grpc_plugin"></a>grpc_plugin |  The location of the Rust protobuf compiler plugin to generate rust gRPC stubs.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | //proto:protoc_gen_rust_grpc |
 | <a id="rust_proto_toolchain-proto_compile_deps"></a>proto_compile_deps |  The crates the generated protobuf libraries depends on.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [Label("//proto/raze:protobuf")] |

docs/rust_repositories.md

@@ -92,7 +92,7 @@ See @rules_rust//rust:repositories.bzl for examples of defining the @rust_cpuX r
 | <a id="rust_toolchain-cargo"></a>cargo |  The location of the <code>cargo</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-clippy_driver"></a>clippy_driver |  The location of the <code>clippy-driver</code> binary. Can be a direct source or a filegroup containing one item.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 | <a id="rust_toolchain-debug_info"></a>debug_info |  Rustc debug info levels per opt level   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {"dbg": "2", "fastbuild": "0", "opt": "0"} |
-| <a id="rust_toolchain-default_edition"></a>default_edition |  The edition to use for rust_* rules that don't specify an edition.   | String | optional | "2018" |
+| <a id="rust_toolchain-default_edition"></a>default_edition |  The edition to use for rust_* rules that don't specify an edition. If absent, every rule is required to specify its <code>edition</code> attribute.   | String | optional | "" |
 | <a id="rust_toolchain-dylib_ext"></a>dylib_ext |  The extension for dynamic libraries created from rustc.   | String | required |  |
 | <a id="rust_toolchain-exec_triple"></a>exec_triple |  The platform triple for the toolchains execution environment. For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations   | String | required |  |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
@@ -133,7 +133,7 @@ A given instance of this rule should be accompanied by a rust_toolchain_reposito
 | <a id="rust_toolchain_repository-name"></a>name |  A unique name for this repository.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
 | <a id="rust_toolchain_repository-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.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_toolchain_repository-dev_components"></a>dev_components |  Whether to download the rustc-dev components (defaults to False). Requires version to be "nightly".   | Boolean | optional | False |
-| <a id="rust_toolchain_repository-edition"></a>edition |  The rust edition to be used by default.   | String | optional | "2018" |
+| <a id="rust_toolchain_repository-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.   | String | optional | "" |
 | <a id="rust_toolchain_repository-exec_triple"></a>exec_triple |  The Rust-style target that this compiler runs on   | String | required |  |
 | <a id="rust_toolchain_repository-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support.   | List of strings | optional | [] |
 | <a id="rust_toolchain_repository-include_rustc_srcs"></a>include_rustc_srcs |  Whether to download and unpack the rustc source files. These are very large, and slow to unpack, but are required to support rust analyzer. An environment variable <code>RULES_RUST_TOOLCHAIN_INCLUDE_RUSTC_SRCS</code> can also be used to control this attribute. This variable will take precedence over the hard coded attribute. Setting it to <code>true</code> to activates this attribute where all other values deactivate it.   | Boolean | optional | False |
@@ -214,7 +214,7 @@ N.B. A "proxy repository" is needed to allow for registering the toolchain (with
 | <a id="rust_repository_set-extra_target_triples"></a>extra_target_triples |  Additional rust-style targets that this set of toolchains should support. Defaults to [].   |  <code>[]</code> |
 | <a id="rust_repository_set-iso_date"></a>iso_date |  The date of the tool. Defaults to None.   |  <code>None</code> |
 | <a id="rust_repository_set-rustfmt_version"></a>rustfmt_version |  The version of rustfmt to be associated with the toolchain. Defaults to None.   |  <code>None</code> |
-| <a id="rust_repository_set-edition"></a>edition |  The rust edition to be used by default (2015, 2018 (if None), or 2021).   |  <code>None</code> |
+| <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.   |  <code>None</code> |
 | <a id="rust_repository_set-dev_components"></a>dev_components |  Whether to download the rustc-dev components. Requires version to be "nightly". Defaults to False.   |  <code>False</code> |
 | <a id="rust_repository_set-sha256s"></a>sha256s |  A dict associating tool subdirectories to sha256 hashes. See [rust_repositories](#rust_repositories) for more details.   |  <code>None</code> |
 | <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). Defaults to ['https://static.rust-lang.org/dist/{}.tar.gz']   |  <code>["https://static.rust-lang.org/dist/{}.tar.gz"]</code> |

proto/toolchain.bzl

@@ -14,8 +14,6 @@
 
 """Toolchain for compiling rust stubs from protobuf and gRPC."""
 
-load("//rust:defs.bzl", "rust_common")
-
 # buildifier: disable=bzl-visibility
 load("//rust/private:utils.bzl", "name_to_crate_name")
 
@@ -146,7 +144,6 @@ rust_proto_toolchain = rule(
     attrs = {
         "edition": attr.string(
             doc = "The edition used by the generated rust source.",
-            default = rust_common.default_edition,
         ),
         "grpc_compile_deps": attr.label_list(
             doc = "The crates the generated grpc libraries depends on.",

rust/private/common.bzl

@@ -25,14 +25,13 @@ In the Bazel lingo, `rust_common` gives the access to the Rust Sandwich API.
 
 load(":providers.bzl", "CrateInfo", "DepInfo", "StdLibInfo")
 
-# These constants only represent the default value for attributes and macros
-# defiend in `rules_rust`. Like any attribute public attribute, they can be
-# overwritten by the user on the rules they're defiend on.
+# This constant only represents the default value for attributes and macros
+# defined in `rules_rust`. Like any attribute public attribute, it can be
+# overwritten by the user on the rules they're defined on.
 #
 # Note: Code in `.github/workflows/crate_universe.yaml` looks for this line, if
 # you remove it or change its format, you will also need to update that code.
 DEFAULT_RUST_VERSION = "1.60.0"
-DEFAULT_RUST_EDITION = "2018"
 
 def _create_crate_info(**kwargs):
     """A constructor for a `CrateInfo` provider
@@ -55,6 +54,5 @@ rust_common = struct(
     crate_info = CrateInfo,
     dep_info = DepInfo,
     stdlib_info = StdLibInfo,
-    default_edition = DEFAULT_RUST_EDITION,
     default_version = DEFAULT_RUST_VERSION,
 )

rust/private/rust.bzl

@@ -106,18 +106,21 @@ def _determine_lib_name(name, crate_type, toolchain, lib_hash = None):
         extension = extension,
     )
 
-def get_edition(attr, toolchain):
+def get_edition(attr, toolchain, label):
     """Returns the Rust edition from either the current rule's attirbutes or the current `rust_toolchain`
 
     Args:
         attr (struct): The current rule's attributes
         toolchain (rust_toolchain): The `rust_toolchain` for the current target
+        label (Label): The label of the target being built
 
     Returns:
         str: The target Rust edition
     """
     if getattr(attr, "edition"):
         return attr.edition
+    elif not toolchain.default_edition:
+        fail("Attribute `edition` is required for {}.".format(label))
     else:
         return toolchain.default_edition
 
@@ -280,7 +283,7 @@ def _rust_library_common(ctx, crate_type):
             proc_macro_deps = depset(proc_macro_deps),
             aliases = ctx.attr.aliases,
             output = rust_lib,
-            edition = get_edition(ctx.attr, toolchain),
+            edition = get_edition(ctx.attr, toolchain, ctx.label),
             rustc_env = ctx.attr.rustc_env,
             is_test = False,
             compile_data = depset(ctx.files.compile_data),
@@ -320,7 +323,7 @@ def _rust_binary_impl(ctx):
             proc_macro_deps = depset(proc_macro_deps),
             aliases = ctx.attr.aliases,
             output = output,
-            edition = get_edition(ctx.attr, toolchain),
+            edition = get_edition(ctx.attr, toolchain, ctx.label),
             rustc_env = ctx.attr.rustc_env,
             is_test = False,
             compile_data = depset(ctx.files.compile_data),
@@ -386,7 +389,7 @@ def _rust_test_common(ctx, toolchain, output):
             proc_macro_deps = depset(proc_macro_deps),
             aliases = ctx.attr.aliases,
             output = output,
-            edition = get_edition(ctx.attr, toolchain),
+            edition = get_edition(ctx.attr, toolchain, ctx.label),
             rustc_env = ctx.attr.rustc_env,
             is_test = True,
             compile_data = depset(ctx.files.compile_data),

rust/repositories.bzl

@@ -101,7 +101,7 @@ def rust_register_toolchains(
 
     Args:
         dev_components (bool, optional): Whether to download the rustc-dev components (defaults to False). Requires version to be "nightly".
-        edition (str, optional): The rust edition to be used by default (2015, 2018 (default), or 2021)
+        edition (str, optional): The rust edition to be used by default (2015, 2018, or 2021). If absent, every rule is required to specify its `edition` attribute.
         include_rustc_srcs (bool, optional): Whether to download rustc's src code. This is required in order to use rust-analyzer support.
             See [rust_toolchain_repository.include_rustc_srcs](#rust_toolchain_repository-include_rustc_srcs). for more details
         iso_date (str, optional): The date of the nightly or beta release (ignored if the version is a specific version).
@@ -212,8 +212,10 @@ rust_toolchain_repository = repository_rule(
             default = False,
         ),
         "edition": attr.string(
-            doc = "The rust edition to be used by default.",
-            default = rust_common.default_edition,
+            doc = (
+                "The rust edition to be used by default (2015, 2018, or 2021). " +
+                "If absent, every rule is required to specify its `edition` attribute."
+            ),
         ),
         "exec_triple": attr.string(
             doc = "The Rust-style target that this compiler runs on",
@@ -311,7 +313,7 @@ def rust_repository_set(
         iso_date (str, optional): The date of the tool. Defaults to None.
         rustfmt_version (str, optional):  The version of rustfmt to be associated with the
             toolchain. Defaults to None.
-        edition (str, optional): The rust edition to be used by default (2015, 2018 (if None), or 2021).
+        edition (str, optional): The rust edition to be used by default (2015, 2018, or 2021). If absent, every rule is required to specify its `edition` attribute.
         dev_components (bool, optional): Whether to download the rustc-dev components.
             Requires version to be "nightly". Defaults to False.
         sha256s (str, optional): A dict associating tool subdirectories to sha256 hashes. See