feat: chdir_binary is an sh_binary that wraps a tool and does a cd first

README.md

@@ -47,6 +47,10 @@ Installation instructions are included on each release:
 - [run_binary](docs/run_binary.md) Like skylib's run_binary but adds directory output support.
 - [stamping](docs/stamping.md) Support version stamping in custom rules.
 
+## Running programs
+
+- [wrap_binary](docs/wrap_binary.md) Compatibility shims which wrap binaries to adapt to the Bazel execution environment.
+
 ## Generating documentation
 
 - [docs](docs/docs.md) Rules for generating docs and stamping tests to ensure they are up to date.

docs/BUILD.bazel

@@ -73,6 +73,11 @@ stardoc_with_diff_test(
     bzl_library_target = "//lib:run_binary",
 )
 
+stardoc_with_diff_test(
+    name = "wrap_binary",
+    bzl_library_target = "//lib:wrap_binary",
+)
+
 stardoc_with_diff_test(
     name = "transitions",
     bzl_library_target = "//lib:transitions",

lib/BUILD.bazel

@@ -123,6 +123,17 @@ bzl_library(
     deps = ["//lib/private:run_binary"],
 )
 
+bzl_library(
+    name = "wrap_binary",
+    srcs = ["wrap_binary.bzl"],
+    deps = [
+        ":paths",
+        ":utils",
+        "//lib/private:run_binary",
+        "@bazel_skylib//rules:write_file",
+    ],
+)
+
 bzl_library(
     name = "repo_utils",
     srcs = ["repo_utils.bzl"],

lib/tests/wrap_binary/BUILD.bazel

@@ -0,0 +1,25 @@
+load("@bazel_skylib//rules:run_binary.bzl", "run_binary")
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
+load("@aspect_bazel_lib//lib:wrap_binary.bzl", "chdir_binary")
+
+sh_binary(
+    name = "fixture",
+    srcs = ["needs-working-dir.sh"],
+)
+
+chdir_binary(
+    name = "wrap",
+    binary = "fixture",
+    chdir = package_name(),
+)
+
+run_binary(
+    name = "assert",
+    outs = ["thing"],
+    tool = "wrap",
+)
+
+build_test(
+    name = "test",
+    targets = ["assert"],
+)

lib/tests/wrap_binary/needs-working-dir.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+if [ "$(dirname $(pwd))" != "wrap_binary" ]; then
+  echo >&2 "this program must be run with the working directory inside the package, but was $(pwd)"
+  exit 1
+fi

lib/wrap_binary.bzl

@@ -0,0 +1,62 @@
+"""Wraps binary rules to make them more compatible with Bazel.
+
+Currently supports only Bash as the wrapper language, not cmd.exe.
+
+Future additions might include:
+- wrap a binary such that it sees a tty on stdin
+- manipulate arguments or environment variables
+- redirect stdout/stderr, e.g. to silence buildspam on success
+- intercept exit code, e.g. to make an "expect_fail"
+- change user, e.g. to deal with containerized build running as root, but tool requires non-root
+- intercept signals, e.g. to make a tool behave as a Bazel persistent worker
+"""
+
+load(":paths.bzl", "BASH_RLOCATION_FUNCTION")
+load(":utils.bzl", "to_label")
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+
+def chdir_binary(name, binary, chdir = "$BUILD_WORKSPACE_DIRECTORY", **kwargs):
+    """Wrap a *_binary to be executed under a given working directory.
+
+    Note: under `bazel run`, this is similar to the `--run_under "cd $PWD &&"` trick, but is hidden
+    from the user so they don't need to know about that flag.
+
+    Args:
+        name: Name of the rule.
+        binary: Label of an executable target to wrap.
+        chdir: Argument for the `cd` command.
+            By default, supports using the binary under `bazel run` by running program in the
+            root of the Bazel workspace, in the source tree.
+        **kwargs: Additional named arguments for the resulting sh_binary rule.
+    """
+
+    script = "_{}_chdir.sh".format(name)
+    binary = to_label(binary)
+
+    # It's 2022 and java_binary still cannot be told to cd to the source directory under bazel run.
+    write_file(
+        name = "_{}_wrap".format(name),
+        out = script,
+        content = [
+            "#!/usr/bin/env bash",
+            BASH_RLOCATION_FUNCTION,
+            # Remove external/ prefix that is included in $(rootpath) but not supported by $(rlocation)
+            "bin=$(rlocation ${1#external/})",
+            # Consume the first argument
+            "shift",
+            # Fix the working directory
+            "cd " + chdir,
+            # Replace the current process
+            "exec $bin $@",
+        ],
+        is_executable = True,
+    )
+
+    native.sh_binary(
+        name = name,
+        srcs = [script],
+        args = ["$(rootpath {})".format(binary)] + kwargs.pop("args", []),
+        data = [binary],
+        deps = ["@bazel_tools//tools/bash/runfiles"],
+        **kwargs
+    )