Add builtin rust platform decls with examples (#144)

* Add builtin rust platform decls with examples

* Remove empty files

* Tidy up

* Add aliases for each OS and each CPU arch as well

* Tidy up

examples/per_platform_printer/BUILD

@@ -0,0 +1,36 @@
+package(default_visibility = ["//visibility:public"])
+
+load(
+    "@io_bazel_rules_rust//rust:rust.bzl",
+    "rust_binary",
+    "rust_library",
+    "rust_test",
+)
+
+rust_binary(
+    name = "print",
+    srcs = ["main.rs"],
+    deps = [
+        ":printer",
+    ],
+)
+
+rust_library(
+    name = "printer",
+    srcs = [
+        "lib.rs",
+        "print_generic.rs",
+    ] + select({
+        "@io_bazel_rules_rust//rust/platform:linux": [
+            ":print_linux.rs",
+        ],
+        "@io_bazel_rules_rust//rust/platform:osx": [
+            ":print_osx.rs",
+        ],
+    }),
+)
+
+rust_test(
+    name = "printer_test",
+    deps = [":printer"],
+)

examples/per_platform_printer/lib.rs

@@ -0,0 +1,41 @@
+mod print_generic;
+
+#[cfg(target_os = "linux")]
+mod print_linux;
+
+#[cfg(target_os="macos")]
+mod print_osx;
+
+pub fn print() -> Vec<String> {
+  let mut outs = Vec::new();
+
+  outs.push(print_generic::print());
+
+  #[cfg(target_os = "linux")]
+  outs.push(print_linux::print());
+
+  #[cfg(target_os="macos")]
+  outs.push(print_osx::print());
+
+  outs
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn prints_correctly() {
+    let outs = print();
+
+    assert_eq!(
+      outs,
+      vec![
+        "Hello Generic!",
+        #[cfg(target_os = "linux")]
+        "Hello Linux!",
+        #[cfg(target_os = "macos")]
+        "Hello OSX!",
+      ]);
+  }
+}

examples/per_platform_printer/main.rs

@@ -0,0 +1,5 @@
+extern crate printer;
+
+fn main() {
+  printer::print();
+}

examples/per_platform_printer/print_generic.rs

@@ -0,0 +1,3 @@
+pub fn print() -> String {
+  "Hello Generic!".to_owned()
+}

examples/per_platform_printer/print_linux.rs

@@ -0,0 +1,3 @@
+pub fn print() -> String {
+  "Hello Linux!".to_owned()
+}

examples/per_platform_printer/print_osx.rs

@@ -0,0 +1,3 @@
+pub fn print() -> String {
+  "Hello OSX!".to_owned()
+}

rust/BUILD

@@ -5,7 +5,6 @@ exports_files([
     "repositories.bzl",
     "rust.bzl",
     "toolchain.bzl",
-    "triple_mappings.bzl",
 ])
 
 toolchain_type(

rust/platform/BUILD

@@ -0,0 +1,5 @@
+package(default_visibility = ["//visibility:public"])
+
+load(":platform.bzl", "declare_config_settings")
+
+declare_config_settings()

rust/platform/platform.bzl

@@ -0,0 +1,81 @@
+load(
+    ":triple_mappings.bzl",
+    "cpu_arch_to_constraints",
+    "system_to_constraints",
+    "triple_to_constraint_set",
+)
+
+# All T1 Platforms should be supported, but aren't, see inline notes.
+_SUPPORTED_T1_PLATFORM_TRIPLES = [
+    "i686-apple-darwin",
+    "i686-pc-windows-gnu",
+    "i686-unknown-linux-gnu",
+    "x86_64-apple-darwin",
+    "x86_64-pc-windows-gnu",
+    "x86_64-unknown-linux-gnu",
+    # N.B. These "alternative" envs are not supported, as bazel cannot distinguish between them
+    # and others using existing @bazel_tools//platforms config_values
+    #
+    #"i686-pc-windows-msvc",
+    #"x86_64-pc-windows-msvc",
+]
+
+# Some T2 Platforms are supported, provided we have mappings to @bazel_tools//platforms entries.
+# See @io_bazel_rules_rust//rust/platform:triple_mappings.bzl for the complete list.
+_SUPPORTED_T2_PLATFORM_TRIPLES = [
+    "aarch64-apple-ios",
+    "aarch64-linux-android",
+    "aarch64-unknown-linux-gnu",
+    "powerpc-unknown-linux-gnu",
+    "arm-unknown-linux-gnueabi",
+    "s390x-unknown-linux-gnu",
+    "i686-linux-android",
+    "i686-unknown-freebsd",
+    "x86_64-apple-ios",
+    "x86_64-linux-android",
+    "x86_64-unknown-freebsd",
+]
+
+_SUPPORTED_CPU_ARCH = [
+    "x86_64",
+    "powerpc",
+    "aarch64",
+    "arm",
+    "i686",
+    "s390x",
+]
+
+_SUPPORTED_SYSTEMS = [
+    "android",
+    "freebsd",
+    "darwin",
+    "ios",
+    "linux",
+    "windows",
+]
+
+def declare_config_settings():
+    for cpu_arch in _SUPPORTED_CPU_ARCH:
+        native.config_setting(
+            name = cpu_arch,
+            constraint_values = cpu_arch_to_constraints(cpu_arch),
+        )
+
+    for system in _SUPPORTED_SYSTEMS:
+        native.config_setting(
+            name = system,
+            constraint_values = system_to_constraints(system),
+        )
+
+    # Add alias for OSX to "darwin" to match what users will be expecting.
+    native.alias(
+        name = "osx",
+        actual = ":darwin",
+    )
+
+    all_supported_triples = _SUPPORTED_T1_PLATFORM_TRIPLES + _SUPPORTED_T2_PLATFORM_TRIPLES
+    for triple in all_supported_triples:
+        native.config_setting(
+            name = triple,
+            constraint_values = triple_to_constraint_set(triple),
+        )

rust/triple_mappings.bzl → rust/platform/triple_mappings.bzl

@@ -63,30 +63,30 @@ _SYSTEM_TO_DYLIB_EXT = {
     "emscripten": ".js",
 }
 
-def _cpu_arch_to_constraints(cpu_arch):
+def cpu_arch_to_constraints(cpu_arch):
     plat_suffix = _CPU_ARCH_TO_BUILTIN_PLAT_SUFFIX[cpu_arch]
 
     if not plat_suffix:
         fail("CPU architecture \"{}\" is not supported by rules_rust".format(cpu_arch))
 
     return ["@bazel_tools//platforms:{}".format(plat_suffix)]
 
-def _vendor_to_constraints(vendor):
+def vendor_to_constraints(vendor):
     # TODO(acmcarther): Review:
     #
     # My current understanding is that vendors can't have a material impact on
     # constraint sets.
     return []
 
-def _system_to_constraints(system):
+def system_to_constraints(system):
     sys_suffix = _SYSTEM_TO_BUILTIN_SYS_SUFFIX[system]
 
     if not sys_suffix:
         fail("System \"{}\" is not supported by rules_rust".format(sys_suffix))
 
     return ["@bazel_tools//platforms:{}".format(sys_suffix)]
 
-def _abi_to_constraints(abi):
+def abi_to_constraints(abi):
     # TODO(acmcarther): Implement when C++ toolchain is more mature and we
     # figure out how they're doing this
     return []
@@ -121,9 +121,9 @@ def triple_to_constraint_set(triple):
         abi = component_parts[3]
 
     constraint_set = []
-    constraint_set += _cpu_arch_to_constraints(cpu_arch)
-    constraint_set += _vendor_to_constraints(vendor)
-    constraint_set += _system_to_constraints(system)
-    constraint_set += _abi_to_constraints(abi)
+    constraint_set += cpu_arch_to_constraints(cpu_arch)
+    constraint_set += vendor_to_constraints(vendor)
+    constraint_set += system_to_constraints(system)
+    constraint_set += abi_to_constraints(abi)
 
     return constraint_set

rust/repositories.bzl

@@ -1,5 +1,5 @@
 load(":known_shas.bzl", "FILE_KEY_TO_SHA")
-load(":triple_mappings.bzl", "system_to_binary_ext", "system_to_dylib_ext", "system_to_staticlib_ext", "triple_to_constraint_set", "triple_to_system")
+load(":platform/triple_mappings.bzl", "system_to_binary_ext", "system_to_dylib_ext", "system_to_staticlib_ext", "triple_to_constraint_set", "triple_to_system")
 
 DEFAULT_TOOLCHAIN_NAME_PREFIX = "toolchain_for"