Set up default allocator_library and global_allocator_library

docs/flatten.md

@@ -1225,7 +1225,7 @@ See `@rules_rust//rust:repositories.bzl` for examples of defining the `@rust_cpu
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_toolchain-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
-| <a id="rust_toolchain-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
+| <a id="rust_toolchain-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>@rules_rust//ffi/cc/allocator_library</code> |
 | <a id="rust_toolchain-binary_ext"></a>binary_ext |  The extension for binaries created from rustc.   | String | required |  |
 | <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/concepts/labels">Label</a> | optional | <code>None</code> |
 | <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/concepts/labels">Label</a> | optional | <code>None</code> |
@@ -1237,7 +1237,7 @@ See `@rules_rust//rust:repositories.bzl` for examples of defining the `@rust_cpu
 | <a id="rust_toolchain-experimental_use_cc_common_link"></a>experimental_use_cc_common_link |  Label to a boolean build setting that controls whether cc_common.link is used to link rust binaries.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>//rust/settings:experimental_use_cc_common_link</code> |
 | <a id="rust_toolchain-extra_exec_rustc_flags"></a>extra_exec_rustc_flags |  Extra flags to pass to rustc in exec configuration   | List of strings | optional | <code>[]</code> |
 | <a id="rust_toolchain-extra_rustc_flags"></a>extra_rustc_flags |  Extra flags to pass to rustc in non-exec configuration   | List of strings | optional | <code>[]</code> |
-| <a id="rust_toolchain-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions for when a global allocator is present.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
+| <a id="rust_toolchain-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions for when a global allocator is present.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>@rules_rust//ffi/cc/global_allocator_library</code> |
 | <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item. If None, rust code is not instrumented for coverage.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
 | <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item. If <code>llvm_cov</code> is None, this can be None as well and rust code is not instrumented for coverage.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
@@ -1300,14 +1300,14 @@ A given instance of this rule should be accompanied by a toolchain_repository_pr
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_toolchain_tools_repository-name"></a>name |  A unique name for this repository.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
-| <a id="rust_toolchain_tools_repository-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | String | optional | <code>""</code> |
+| <a id="rust_toolchain_tools_repository-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | String | optional | <code>"@rules_rust//ffi/cc/allocator_library"</code> |
 | <a id="rust_toolchain_tools_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/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="rust_toolchain_tools_repository-dev_components"></a>dev_components |  Whether to download the rustc-dev components (defaults to False). Requires version to be "nightly".   | Boolean | optional | <code>False</code> |
 | <a id="rust_toolchain_tools_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 | <code>""</code> |
 | <a id="rust_toolchain_tools_repository-exec_triple"></a>exec_triple |  The Rust-style target that this compiler runs on   | String | required |  |
 | <a id="rust_toolchain_tools_repository-extra_exec_rustc_flags"></a>extra_exec_rustc_flags |  Extra flags to pass to rustc in exec configuration   | List of strings | optional | <code>[]</code> |
 | <a id="rust_toolchain_tools_repository-extra_rustc_flags"></a>extra_rustc_flags |  Extra flags to pass to rustc in non-exec configuration   | List of strings | optional | <code>[]</code> |
-| <a id="rust_toolchain_tools_repository-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions when a global allocator is used with cc_common.link.   | String | optional | <code>""</code> |
+| <a id="rust_toolchain_tools_repository-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions when a global allocator is used with cc_common.link.   | String | optional | <code>"@rules_rust//ffi/cc/global_allocator_library"</code> |
 | <a id="rust_toolchain_tools_repository-iso_date"></a>iso_date |  The date of the tool (or None, if the version is a specific version).   | String | optional | <code>""</code> |
 | <a id="rust_toolchain_tools_repository-opt_level"></a>opt_level |  Rustc optimization levels. For more details see the documentation for <code>rust_toolchain.opt_level</code>.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="rust_toolchain_tools_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 |  |

docs/rust_repositories.md

@@ -93,7 +93,7 @@ See `@rules_rust//rust:repositories.bzl` for examples of defining the `@rust_cpu
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_toolchain-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
-| <a id="rust_toolchain-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
+| <a id="rust_toolchain-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>@rules_rust//ffi/cc/allocator_library</code> |
 | <a id="rust_toolchain-binary_ext"></a>binary_ext |  The extension for binaries created from rustc.   | String | required |  |
 | <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/concepts/labels">Label</a> | optional | <code>None</code> |
 | <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/concepts/labels">Label</a> | optional | <code>None</code> |
@@ -105,7 +105,7 @@ See `@rules_rust//rust:repositories.bzl` for examples of defining the `@rust_cpu
 | <a id="rust_toolchain-experimental_use_cc_common_link"></a>experimental_use_cc_common_link |  Label to a boolean build setting that controls whether cc_common.link is used to link rust binaries.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>//rust/settings:experimental_use_cc_common_link</code> |
 | <a id="rust_toolchain-extra_exec_rustc_flags"></a>extra_exec_rustc_flags |  Extra flags to pass to rustc in exec configuration   | List of strings | optional | <code>[]</code> |
 | <a id="rust_toolchain-extra_rustc_flags"></a>extra_rustc_flags |  Extra flags to pass to rustc in non-exec configuration   | List of strings | optional | <code>[]</code> |
-| <a id="rust_toolchain-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions for when a global allocator is present.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
+| <a id="rust_toolchain-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions for when a global allocator is present.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>@rules_rust//ffi/cc/global_allocator_library</code> |
 | <a id="rust_toolchain-llvm_cov"></a>llvm_cov |  The location of the <code>llvm-cov</code> binary. Can be a direct source or a filegroup containing one item. If None, rust code is not instrumented for coverage.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
 | <a id="rust_toolchain-llvm_profdata"></a>llvm_profdata |  The location of the <code>llvm-profdata</code> binary. Can be a direct source or a filegroup containing one item. If <code>llvm_cov</code> is None, this can be None as well and rust code is not instrumented for coverage.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
 | <a id="rust_toolchain-llvm_tools"></a>llvm_tools |  LLVM tools that are shipped with the Rust toolchain.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional | <code>None</code> |
@@ -168,14 +168,14 @@ A given instance of this rule should be accompanied by a toolchain_repository_pr
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_toolchain_tools_repository-name"></a>name |  A unique name for this repository.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
-| <a id="rust_toolchain_tools_repository-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | String | optional | <code>""</code> |
+| <a id="rust_toolchain_tools_repository-allocator_library"></a>allocator_library |  Target that provides allocator functions when rust_library targets are embedded in a cc_binary.   | String | optional | <code>"@rules_rust//ffi/cc/allocator_library"</code> |
 | <a id="rust_toolchain_tools_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/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="rust_toolchain_tools_repository-dev_components"></a>dev_components |  Whether to download the rustc-dev components (defaults to False). Requires version to be "nightly".   | Boolean | optional | <code>False</code> |
 | <a id="rust_toolchain_tools_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 | <code>""</code> |
 | <a id="rust_toolchain_tools_repository-exec_triple"></a>exec_triple |  The Rust-style target that this compiler runs on   | String | required |  |
 | <a id="rust_toolchain_tools_repository-extra_exec_rustc_flags"></a>extra_exec_rustc_flags |  Extra flags to pass to rustc in exec configuration   | List of strings | optional | <code>[]</code> |
 | <a id="rust_toolchain_tools_repository-extra_rustc_flags"></a>extra_rustc_flags |  Extra flags to pass to rustc in non-exec configuration   | List of strings | optional | <code>[]</code> |
-| <a id="rust_toolchain_tools_repository-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions when a global allocator is used with cc_common.link.   | String | optional | <code>""</code> |
+| <a id="rust_toolchain_tools_repository-global_allocator_library"></a>global_allocator_library |  Target that provides allocator functions when a global allocator is used with cc_common.link.   | String | optional | <code>"@rules_rust//ffi/cc/global_allocator_library"</code> |
 | <a id="rust_toolchain_tools_repository-iso_date"></a>iso_date |  The date of the tool (or None, if the version is a specific version).   | String | optional | <code>""</code> |
 | <a id="rust_toolchain_tools_repository-opt_level"></a>opt_level |  Rustc optimization levels. For more details see the documentation for <code>rust_toolchain.opt_level</code>.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional | <code>{}</code> |
 | <a id="rust_toolchain_tools_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 |  |

examples/android/BUILD.bazel

@@ -2,17 +2,10 @@ load("@build_bazel_rules_android//android:rules.bzl", "android_binary", "android
 load("@rules_cc//cc:defs.bzl", "cc_library")
 load("@rules_rust//rust:defs.bzl", "rust_library")
 
-cc_library(
-    name = "allocator_library",
-    srcs = ["allocator_library.cc"],
-    visibility = ["//visibility:public"],
-)
-
 rust_library(
     name = "rust_lib",
     srcs = ["demo.rs"],
     edition = "2018",
-    deps = [":allocator_library"],
 )
 
 cc_library(

examples/ios/BUILD.bazel

@@ -3,18 +3,11 @@ load("@build_bazel_rules_apple//apple:macos.bzl", "macos_application")
 load("@rules_cc//cc:defs.bzl", "cc_library", "objc_library")
 load("@rules_rust//rust:defs.bzl", "rust_library")
 
-cc_library(
-    name = "allocator_library",
-    srcs = ["allocator_library.cc"],
-    tags = ["manual"],
-)
-
 rust_library(
     name = "rust_lib",
     srcs = ["demo.rs"],
     edition = "2018",
     tags = ["manual"],
-    deps = [":allocator_library"],
 )
 
 # TODO: Remove this once rules_rust doesn't support bazel 5.x

ffi/cc/allocator_library/BUILD.bazel

@@ -0,0 +1,14 @@
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+cc_library(
+    name = "allocator_library",
+    srcs = select({
+        # Windows doesn't support weak symbol linkage.
+        # If someone can make this work on Windows, please do!
+        # For now we will silently not supply any symbols, because it would be very messy to conditionally define the default allocator library on toolchains depending on the platform.
+        "@platforms//os:windows": ["empty.cc"],
+        "//conditions:default": ["allocator_library.cc"],
+    }),
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)