ci: add test coverage for format binary

This is a beginning, if the pattern works I'll apply it to remaining languages.
Should be able to catch most regressions this way.

.github/workflows/ci.yaml

@@ -38,6 +38,9 @@ jobs:
           support-version: "0.3.0"
           assert-path: /usr/lib/bats/bats-assert
           assert-version: "2.1.0"
-      - name: Integration test
+      - name: "Integration test: example"
         working-directory: example
         run: bats ./test
+      - name: "Integration test: format"
+        working-directory: format
+        run: bats ./test

format/private/format.sh

@@ -22,6 +22,8 @@ function on_exit {
 
 trap on_exit EXIT
 
+set -o noglob
+
 # ls-files <language> [<file>...]
 function ls-files {
     language="$1" && shift;

format/private/formatter_binary.bzl

@@ -3,7 +3,7 @@
 load("@aspect_bazel_lib//lib:paths.bzl", "BASH_RLOCATION_FUNCTION", "to_rlocation_path")
 
 # Per the formatter design, each language can only have a single formatter binary
-_TOOLS = {
+TOOLS = {
     "javascript": "prettier",
     "markdown": "prettier-md",
     "python": "ruff",
@@ -22,16 +22,20 @@ _TOOLS = {
 }
 
 def _formatter_binary_impl(ctx):
-    # We need to fill in the rlocation paths in the shell script
-    substitutions = {
-        "{{BASH_RLOCATION_FUNCTION}}": BASH_RLOCATION_FUNCTION,
-        "{{fix_target}}": str(ctx.label),
-    }
-    tools = {v: getattr(ctx.attr, k) for k, v in _TOOLS.items()}
+    substitutions = {}
+    tools = {v: getattr(ctx.attr, k) for k, v in TOOLS.items()}
     for tool, attr in tools.items():
         if attr:
             substitutions["{{%s}}" % tool] = to_rlocation_path(ctx, attr.files_to_run.executable)
+    if len(substitutions) == 0:
+        fail("multi_formatter_binary should have at least one language attribute set to a formatter tool")
 
+    substitutions.update({
+        # We need to fill in the rlocation paths in the shell script
+        "{{BASH_RLOCATION_FUNCTION}}": BASH_RLOCATION_FUNCTION,
+        # Support helpful error reporting
+        "{{fix_target}}": str(ctx.label),
+    })
     bin = ctx.actions.declare_file("format.sh")
     ctx.actions.expand_template(
         template = ctx.file._bin,
@@ -66,7 +70,7 @@ formatter_binary_lib = struct(
     implementation = _formatter_binary_impl,
     attrs = dict({
         k: attr.label(doc = "a binary target that runs {} (or another tool with compatible CLI arguments)".format(v), executable = True, cfg = "exec", allow_files = True)
-        for k, v in _TOOLS.items()
+        for k, v in TOOLS.items()
     }, **{
         "_bin": attr.label(default = "//format/private:format.sh", allow_single_file = True),
         "_runfiles_lib": attr.label(default = "@bazel_tools//tools/bash/runfiles", allow_single_file = True),

format/test/BUILD.bazel

@@ -0,0 +1,36 @@
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+load("//format:defs.bzl", "multi_formatter_binary")
+load("//format/private:formatter_binary.bzl", "TOOLS")
+
+# Avoid depending on a bunch of actual tools in the root module.
+# That's the job of the example/ submodule.
+# Instead, just provide a tool that acts like any of the formatters we support.
+[
+    write_file(
+        name = "fake_{}_sh".format(t),
+        out = "fake_{}.sh".format(t),
+        content = [
+            "#!/usr/bin/env bash",
+            "echo + {} $*".format(t),
+        ],
+    )
+    for t in TOOLS.values()
+]
+
+[
+    sh_binary(
+        name = "fake_" + t,
+        srcs = ["fake_{}.sh".format(t)],
+    )
+    for t in TOOLS.values()
+]
+
+multi_formatter_binary(
+    name = "format_javascript",
+    javascript = ":fake_prettier",
+)
+
+multi_formatter_binary(
+    name = "format_starlark",
+    starlark = ":fake_buildifier",
+)

format/test/format_test.bats

@@ -0,0 +1,29 @@
+bats_load_library "bats-support"
+bats_load_library "bats-assert"
+
+@test "should run prettier on javascript" {
+    run bazel run //format/test:format_javascript
+    assert_success
+
+    echo <<"EOF" | assert_output --partial
+Formatting JavaScript with Prettier...
++ prettier --write example/.eslintrc.cjs
+EOF    
+    echo <<"EOF" | assert_output --partial
+Formatting TypeScript with Prettier...
++ prettier --write example/src/file.ts example/test/no_violations.ts
+EOF
+    echo <<"EOF" | assert_output --partial
+Formatting TSX with Prettier...
++ prettier --write example/src/hello.tsx
+EOF
+}
+
+@test "should run buildozer on starlark" {
+    run bazel run //format/test:format_starlark
+    assert_success
+    assert_output --partial "Formatting Starlark with Buildifier..."
+    assert_output --partial "+ buildifier -mode=fix BUILD.bazel"
+    assert_output --partial "format/private/BUILD.bazel"
+
+}