Support change-dir before calling a command (#14)

Changes the bash script generated by `command` to look up the target
executable in the runfiles.

Closes #13

command.bzl

@@ -15,6 +15,16 @@ _force_opt = transition(
     outputs = ["//command_line_option:compilation_mode"],
 )
 
+def _rlocation_path(ctx, file):
+    """Produce the rlocation lookup path for the given file.
+
+    See https://github.com/bazelbuild/bazel-skylib/issues/303.
+    """
+    if file.short_path.startswith("../"):
+        return file.short_path[3:]
+    else:
+        return ctx.workspace_name + "/" + file.short_path
+
 def _command_impl(ctx):
     runfiles = ctx.runfiles().merge(ctx.attr._bash_runfiles[DefaultInfo].default_runfiles)
 
@@ -40,7 +50,7 @@ def _command_impl(ctx):
         "%s" % shell.quote(ctx.expand_location(v, targets = expansion_targets))
         for v in ctx.attr.arguments
     ]
-    command_exec = " ".join(["exec ./%s" % shell.quote(executable.short_path)] + str_args + ['"$@"\n'])
+    command_exec = " ".join(["exec $(rlocation %s)" % shell.quote(_rlocation_path(ctx, executable))] + str_args + ['"$@"\n'])
 
     out_file = ctx.actions.declare_file(ctx.label.name + ".bash")
     ctx.actions.write(

tests/BUILD

@@ -21,6 +21,21 @@ command(
     command = "validate_args",
 )
 
+sh_binary(
+    name = "validate_chdir_location",
+    srcs = ["validate-chdir-location.sh"],
+    deps = ["@bazel_tools//tools/bash/runfiles"],
+)
+
+command(
+    name = "validate_chdir_location_cmd",
+    # Note, from Bazel 6.1.0 upwards this can be replaced by $(rlocationpath ...).
+    # See https://github.com/bazelbuild/bazel/pull/16653.
+    arguments = ["rules_multirun/$(rootpath :hello)"],
+    command = "validate_chdir_location",
+    data = [":hello"],
+)
+
 sh_binary(
     name = "validate_env",
     srcs = ["validate-env.sh"],
@@ -67,6 +82,7 @@ sh_test(
         ":multirun_serial",
         ":multirun_serial_no_print",
         ":validate_args_cmd",
+        ":validate_chdir_location_cmd",
         ":validate_env_cmd",
     ],
     deps = ["@bazel_tools//tools/bash/runfiles"],

tests/test.sh

@@ -23,6 +23,8 @@ fi
 
 script=$(rlocation rules_multirun/tests/validate_args_cmd.bash)
 $script
+script=$(rlocation rules_multirun/tests/validate_chdir_location_cmd.bash)
+$script
 script=$(rlocation rules_multirun/tests/validate_env_cmd.bash)
 $script
 

tests/validate-chdir-location.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+# --- begin runfiles.bash initialization v2 ---
+# Copy-pasted from the Bazel Bash runfiles library v2.
+set -uo pipefail; set +e; f=bazel_tools/tools/bash/runfiles/runfiles.bash
+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 $f"; exit 1; }; f=; set -e
+# --- end runfiles.bash initialization v2 ---
+
+set -euo pipefail
+
+WORKDIR="$(mktemp -d)"
+trap 'rm -rf -- "$WORKDIR"' EXIT
+cd "$WORKDIR"
+
+if [[ $# != 1 ]]; then
+  echo "error: expected one argument, got $#"
+  exit 1
+fi
+
+hello="$(rlocation "$1")"
+output="$($hello)"
+
+if [[ "$output" != hello ]]; then
+  echo "error: expected '$hello' to print 'hello', got '$output'"
+  exit 1
+fi