Add support for location expansion in args (#100)

See the long comment in `args.bzl` for an explanation of why this is so
complicated.

Fixes #82

MODULE.bazel

@@ -8,7 +8,7 @@ bazel_dep(name = "bazel_skylib", version = "1.4.1")
 
 bazel_dep(name = "aspect_bazel_lib", version = "1.34.0", dev_dependency = True)
 bazel_dep(name = "bazel_skylib_gazelle_plugin", version = "1.4.1", dev_dependency = True)
-bazel_dep(name = "buildifier_prebuilt", version = "6.1.0", dev_dependency = True)
+bazel_dep(name = "buildifier_prebuilt", version = "6.4.0", dev_dependency = True)
 bazel_dep(name = "gazelle", version = "0.33.0", dev_dependency = True, repo_name = "bazel_gazelle")
 bazel_dep(name = "platforms", version = "0.0.6", dev_dependency = True)
 bazel_dep(name = "rules_testing", version = "0.4.0", dev_dependency = True)

examples/MODULE.bazel

@@ -6,6 +6,7 @@ local_path_override(
     path = "..",
 )
 
+bazel_dep(name = "bazel_skylib", version = "1.6.1")
 bazel_dep(name = "contrib_rules_jvm", version = "0.27.0")
 bazel_dep(name = "platforms", version = "0.0.10")
 bazel_dep(name = "rules_cc", version = "0.0.9")

examples/args_location_expansion/BUILD.bazel

@@ -0,0 +1,58 @@
+load("//args_location_expansion/rules:defs.bzl", "write_settings_rule")
+load(":doubly_transitioned_test.bzl", "doubly_transitioned_test")
+
+write_settings_rule(
+    name = "single_rule",
+    tags = ["manual"],
+)
+
+alias(
+    name = "alias_target",
+    actual = "//args_location_expansion/pkg:aliased_rule",
+    tags = ["manual"],
+)
+
+doubly_transitioned_test(
+    name = "doubly_transitioned_test",
+    args = [
+        "$(rlocationpath :source_file.txt)",
+        "$(rlocationpath :single_rule)",
+        "$(rlocationpaths //args_location_expansion/pkg:multiple_rules)",
+        "$(rlocationpath alias_target)",
+        "$(rlocationpath :alias_target)",
+        "$(rlocationpath @bazel_tools//tools/bash/runfiles)",
+        "_main/$(rootpath :single_rule)",
+        "_main/$(location :single_rule)",
+    ] + select({
+        "@platforms//os:linux": ["$(rlocationpath //args_location_expansion/pkg:linux_only_rule)"],
+        "//conditions:default": ["$(rlocationpath //args_location_expansion/pkg:generic_rule)"],
+    }) + select({
+        "@platforms//os:windows": [],
+        "//conditions:default": ["$(rlocationpath //args_location_expansion/pkg:special_09!%-@^_\"#$&'(*-+,;<=>?[]{|}~/._characters_rule)"],
+    }),
+    binary = ":test_bin",
+    data = [
+        ":alias_target",
+        ":single_rule",
+        ":source_file.txt",
+        "//args_location_expansion/pkg:multiple_rules",
+        "@bazel_tools//tools/bash/runfiles",
+    ] + select({
+        "@platforms//os:linux": ["//args_location_expansion/pkg:linux_only_rule"],
+        "//conditions:default": ["//args_location_expansion/pkg:generic_rule"],
+    }) + select({
+        "@platforms//os:windows": [],
+        "//conditions:default": ["//args_location_expansion/pkg:special_09!%-@^_\"#$&'(*-+,;<=>?[]{|}~/._characters_rule"],
+    }),
+    env = select({
+        "@platforms//os:windows": {"NUM_RUNFILES": "10"},
+        "//conditions:default": {"NUM_RUNFILES": "11"},
+    }),
+)
+
+sh_binary(
+    name = "test_bin",
+    srcs = ["test_bin.sh"],
+    data = ["@bazel_tools//tools/bash/runfiles"],
+    visibility = ["//visibility:public"],
+)

examples/args_location_expansion/doubly_transitioned_test.bzl

@@ -0,0 +1,6 @@
+load("@with_cfg.bzl", "with_cfg")
+load("//args_location_expansion/rules:defs.bzl", "transitioned_test")
+
+_builder = with_cfg(transitioned_test)
+_builder.set(Label("//args_location_expansion/rules:with_cfg_setting"), "with_cfg")
+doubly_transitioned_test, _doubly_transitioned_test_ = _builder.build()

examples/args_location_expansion/pkg/BUILD.bazel

@@ -0,0 +1,46 @@
+load("//args_location_expansion/rules:defs.bzl", "write_settings_rule")
+
+write_settings_rule(
+    name = "some_rule",
+    tags = ["manual"],
+)
+
+write_settings_rule(
+    name = "other_rule",
+    tags = ["manual"],
+)
+
+filegroup(
+    name = "multiple_rules",
+    srcs = [
+        ":other_rule",
+        ":some_rule",
+    ],
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)
+
+write_settings_rule(
+    name = "aliased_rule",
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)
+
+write_settings_rule(
+    # Omits ')' as it doesn't seem to be supported with location expansion.
+    name = "special_09!%-@^_\"#$&'(*-+,;<=>?[]{|}~/._characters_rule",
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)
+
+write_settings_rule(
+    name = "linux_only_rule",
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)
+
+write_settings_rule(
+    name = "generic_rule",
+    tags = ["manual"],
+    visibility = ["//visibility:public"],
+)

examples/args_location_expansion/rules/BUILD.bazel

@@ -0,0 +1,13 @@
+load("@bazel_skylib//rules:common_settings.bzl", "string_setting")
+
+string_setting(
+    name = "rule_setting",
+    build_setting_default = "unset",
+    visibility = ["//visibility:public"],
+)
+
+string_setting(
+    name = "with_cfg_setting",
+    build_setting_default = "unset",
+    visibility = ["//visibility:public"],
+)

examples/args_location_expansion/rules/defs.bzl

@@ -0,0 +1,71 @@
+load("@bazel_skylib//rules:common_settings.bzl", "BuildSettingInfo")
+
+def _write_settings_rule_impl(ctx):
+    # type: (ctx) -> None
+    rule_setting = ctx.attr._rule_setting[BuildSettingInfo].value
+    if rule_setting == "unset":
+        fail("rule_setting is unset")
+    with_cfg_setting = ctx.attr._with_cfg_setting[BuildSettingInfo].value
+    if with_cfg_setting == "unset":
+        fail("with_cfg_setting is unset")
+
+    out = ctx.actions.declare_file(ctx.label.name + "_" + rule_setting[0] + "_" + with_cfg_setting[0])
+    ctx.actions.write(out, "name:{},rule_setting:{},with_cfg_setting:{}\n".format(out.basename, rule_setting, with_cfg_setting))
+    return [DefaultInfo(files = depset([out]))]
+
+write_settings_rule = rule(
+    implementation = _write_settings_rule_impl,
+    attrs = {
+        "_rule_setting": attr.label(default = ":rule_setting"),
+        "_with_cfg_setting": attr.label(default = ":with_cfg_setting"),
+    },
+)
+
+def _data_transition_impl(_settings, _attr):
+    return {
+        "//args_location_expansion/rules:rule_setting": "rule",
+    }
+
+_data_transition = transition(
+    implementation = _data_transition_impl,
+    inputs = ["//args_location_expansion/rules:rule_setting"],
+    outputs = ["//args_location_expansion/rules:rule_setting"],
+)
+
+def _transitioned_test_impl(ctx):
+    # type: (ctx) -> None
+    executable = ctx.actions.declare_file(ctx.label.name)
+    ctx.actions.symlink(output = executable, target_file = ctx.executable.binary)
+    runfiles = ctx.runfiles()
+    runfiles = runfiles.merge(ctx.attr.binary[DefaultInfo].default_runfiles)
+    for target in ctx.attr.data:
+        runfiles = runfiles.merge(ctx.runfiles(transitive_files = target[DefaultInfo].files))
+        runfiles = runfiles.merge(target[DefaultInfo].data_runfiles)
+    return [
+        DefaultInfo(
+            executable = executable,
+            runfiles = runfiles,
+        ),
+        RunEnvironmentInfo(
+            environment = ctx.attr.env,
+        ),
+    ]
+
+transitioned_test = rule(
+    implementation = _transitioned_test_impl,
+    attrs = {
+        "binary": attr.label(
+            cfg = "target",
+            executable = True,
+        ),
+        "data": attr.label_list(
+            cfg = _data_transition,
+            allow_files = True,
+        ),
+        "env": attr.string_dict(),
+        "_allowlist_function_transition": attr.label(
+            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+        ),
+    },
+    test = True,
+)

examples/args_location_expansion/source_file.txt

@@ -0,0 +1 @@
+name:source_file.txt,rule_setting:rule,with_cfg_setting:with_cfg

examples/args_location_expansion/test_bin.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+# --- begin runfiles.bash initialization v3 ---
+# Copy-pasted from the Bazel Bash runfiles library v3.
+set -uo pipefail; set +e; f=bazel_tools/tools/bash/runfiles/runfiles.bash
+# shellcheck disable=SC1090
+source "${RUNFILES_DIR:-/dev/null}/$f" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "${RUNFILES_MANIFEST_FILE:-/dev/null}" | cut -f2- -d' ')" 2>/dev/null || \
+  source "$0.runfiles/$f" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "$0.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "$0.exe.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+  { echo>&2 "ERROR: cannot find $f"; exit 1; }; f=; set -e
+# --- end runfiles.bash initialization v3 ---
+
+function check_runfile() {
+  real_path=$(rlocation "$1" || { >&2 echo "$1 not found"; exit 1; })
+  basename=$(basename "$1")
+  want="name:$basename,rule_setting:rule,with_cfg_setting:with_cfg"
+  if [[ $1 != bazel_tools/* && "$(cat "$real_path")" != "$want" ]]; then
+    echo "Runfile content mismatch in $1: got '$(cat "$real_path")', want '$want'"
+    exit 1
+  fi
+}
+
+if [ "$#" -ne "$NUM_RUNFILES" ]; then
+  echo "Unexpected number of arguments: $#, want $NUM_RUNFILES"
+  exit 1
+fi
+for arg in "$@"; do
+  check_runfile "$arg"
+done

with_cfg/private/BUILD.bazel

@@ -20,6 +20,15 @@ config_setting(
     },
 )
 
+bzl_library(
+    name = "args",
+    srcs = ["args.bzl"],
+    visibility = ["//with_cfg:__subpackages__"],
+    deps = [
+        ":rewrite",
+    ],
+)
+
 bzl_library(
     name = "builder",
     srcs = ["builder.bzl"],
@@ -136,6 +145,7 @@ bzl_library(
     srcs = ["wrapper.bzl"],
     visibility = ["//with_cfg:__subpackages__"],
     deps = [
+        ":args",
         ":rewrite",
         ":select",
         ":setting",