fix: resolve rb_binary main scripts from any working directory

.github/workflows/ci.yml

@@ -95,6 +95,13 @@ jobs:
         with:
           name: coverage-${{ matrix.os }}-${{ matrix.ruby }}
           path: examples/gem/bazel-testlogs/spec/add/coverage.dat
+      # rb_binary launchers must resolve the main script from any working
+      # directory, not only under `bazel run` defaults.
+      - run: |
+          launcher="$PWD/$(bazel cquery --output=starlark --starlark:expr='target.files_to_run.executable.path' lib/gem:add-numbers)"
+          cd /
+          "$launcher" 1 2
+        if: matrix.os != 'windows-latest'
       - if: failure() && runner.debug == '1'
         uses: mxschmitt/action-tmate@v3
 

ruby/private/binary.bzl

@@ -81,6 +81,7 @@ def generate_rb_binary_script(ctx, binary, bundler = False, args = [], env = {},
         toolchain = ctx.attr.ruby[platform_common.ToolchainInfo]
 
     binary_path = ""
+    binary_fallback_path = ""
     locate_binary_in_runfiles = ""
     ruby_binary_name = toolchain.ruby.basename
     if binary and binary != toolchain.ruby:
@@ -90,11 +91,22 @@ def generate_rb_binary_script(ctx, binary, bundler = False, args = [], env = {},
         # so for now we skip locating the binary in runfiles. This only prevents
         # running binary scripts directly and should not affect normal `bazel run`.
         # See BATCH_RLOCATION_FUNCTION comments for more details.
-        if binary_path.startswith("../") and not _is_windows(ctx):
-            binary_path = _to_rlocation_path(ctx, binary)
-            locate_binary_in_runfiles = "true"
-        else:
+        if _is_windows(ctx):
             binary_path = _normalize_path(ctx, binary_path)
+        else:
+            binary_path = _to_rlocation_path(ctx, binary)
+
+            # Binaries outside the main repository are always expected to be
+            # locatable through runfiles. Binaries in the main repository are
+            # resolved through runfiles when possible, so that they can be
+            # executed from any working directory (e.g. via --run_under or by
+            # running the launcher directly), and fall back to the relative
+            # path, which requires the default `bazel run` working directory.
+            if binary.short_path.startswith("../"):
+                locate_binary_in_runfiles = "true"
+            else:
+                binary_fallback_path = _normalize_path(ctx, binary.short_path)
+                locate_binary_in_runfiles = "fallback"
 
         # JRuby's .cmd stubs are plain batch files, so they must be executed
         # directly. MRI's are Ruby polyglots and only work via the interpreter.
@@ -130,6 +142,7 @@ def generate_rb_binary_script(ctx, binary, bundler = False, args = [], env = {},
         substitutions = {
             "{args}": args,
             "{binary}": binary_path,
+            "{binary_fallback}": binary_fallback_path,
             "{env}": _convert_env_to_script(ctx, environment),
             "{bundler_command}": bundler_command,
             "{jars_home_strip_suffix}": jars_home_strip_suffix,

ruby/private/binary/binary.sh.tpl

@@ -76,10 +76,15 @@ if [ -n "{bundler_command}" ]; then
   fi
 fi
 
-if [ -n "{locate_binary_in_runfiles}" ]; then
+if [ "{locate_binary_in_runfiles}" = "true" ]; then
   binary="$(rlocation "{binary}")" \
     || (fail "Failed to locate {binary} in the runfiles." \
       "Did you forget to add the binary to the deps?")
+elif [ "{locate_binary_in_runfiles}" = "fallback" ]; then
+  binary="$(rlocation "{binary}" 2>/dev/null || true)"
+  if [ -z "$binary" ] || [ ! -f "$binary" ]; then
+    binary="{binary_fallback}"
+  fi
 else
   binary="{binary}"
 fi