Create a test rule that compares CToolchains from CROSSTOOL file and from Starlark rule

Work towards issue #5380
RELNOTES: None
PiperOrigin-RevId: 229928313

tools/migration/ctoolchain_compare.bzl

@@ -0,0 +1,49 @@
+"""A test rule that compares two CToolchains in proto format."""
+
+def _impl(ctx):
+    toolchain_config_proto = ctx.actions.declare_file("toolchain_config.proto")
+    ctx.actions.write(
+        toolchain_config_proto,
+        ctx.attr.toolchain_config[CcToolchainConfigInfo].proto,
+    )
+
+    script = ("%s --before='%s' --after='%s' --toolchain_identifier='%s'" % (
+        ctx.executable._comparator.short_path,
+        ctx.file.crosstool.short_path,
+        toolchain_config_proto.short_path,
+        ctx.attr.toolchain_identifier,
+    ))
+    test_executable = ctx.actions.declare_file(ctx.label.name)
+    ctx.actions.write(test_executable, script, is_executable = True)
+
+    runfiles = ctx.runfiles(files = [toolchain_config_proto, ctx.file.crosstool])
+    runfiles = runfiles.merge(ctx.attr._comparator[DefaultInfo].default_runfiles)
+
+    return DefaultInfo(runfiles = runfiles, executable = test_executable)
+
+cc_toolchains_compare_test = rule(
+    implementation = _impl,
+    attrs = {
+        "crosstool": attr.label(
+            mandatory = True,
+            allow_single_file = True,
+            doc = "Location of the CROSSTOOL file",
+        ),
+        "toolchain_config": attr.label(
+            mandatory = True,
+            providers = [CcToolchainConfigInfo],
+            doc = ("Starlark rule that replaces the CROSSTOOL file functionality " +
+                   "for the CToolchain with the given identifier"),
+        ),
+        "toolchain_identifier": attr.string(
+            mandatory = True,
+            doc = "identifier of the CToolchain that is being compared",
+        ),
+        "_comparator": attr.label(
+            default = ":ctoolchain_comparator",
+            executable = True,
+            cfg = "host",
+        ),
+    },
+    test = True,
+)