test: add unit tests for kotlinc/javac opts flag mapping

Tests all three code paths in convert._to_flags:
- value_to_flag dict lookup (warn, include_stdlibs, release)
- map_value_to_flag fn (jvm_target, x_backend_threads, x_optin, x_warning_level)
- derive.info path (x_suppress_warning, x_lint, add_exports, annotation_processor_options)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: restingbull

src/test/starlark/BUILD.bazel

@@ -1,9 +1,12 @@
 load("//src/test/starlark/internal/jvm:resource_strip_prefix_test.bzl", "strip_resource_prefix_test_suite")
 load("//src/test/starlark/internal/lint:ktlint_fix_runfiles_test.bzl", "ktlint_fix_runfiles_test_suite")
 load(":convert_test.bzl", "convert_test_suite")
+load(":opts_test.bzl", "opts_test_suite")
 
 convert_test_suite(name = "convert_tests")
 
+opts_test_suite(name = "opts_tests")
+
 strip_resource_prefix_test_suite(name = "resource_strip_prefix_tests")
 
 ktlint_fix_runfiles_test_suite(name = "ktlint_fix_runfiles_tests")
@@ -13,6 +16,7 @@ test_suite(
     tests = [
         ":convert_tests",
         ":ktlint_fix_runfiles_tests",
+        ":opts_tests",
         ":resource_strip_prefix_tests",
         "//src/test/starlark/ksp:ksp_tests",
     ],

src/test/starlark/opts_test.bzl

@@ -0,0 +1,59 @@
+load("@bazel_skylib//lib:unittest.bzl", "asserts", "unittest")
+load("//src/main/starlark/core/options:opts.javac.bzl", "javac_options_to_flags")
+load("//src/main/starlark/core/options:opts.kotlinc.bzl", "kotlinc_options_to_flags")
+
+# x_backend_threads and x_optin require non-None values (map_value_to_flag fails with None)
+def _kopts(**kwargs):
+    base = {"x_backend_threads": 1, "x_optin": []}
+    base.update(kwargs)
+    return struct(**base)
+
+def _kotlinc_flags_impl(ctx):
+    env = unittest.begin(ctx)
+
+    # map_value_to_flag path
+    asserts.equals(env, ["-jvm-target=17"], kotlinc_options_to_flags(_kopts(jvm_target = "17")))
+    asserts.equals(env, ["-Xbackend-threads=4"], kotlinc_options_to_flags(_kopts(x_backend_threads = 4)))
+    asserts.equals(env, ["-opt-in=A", "-opt-in=B"], kotlinc_options_to_flags(_kopts(x_optin = ["A", "B"])))
+    asserts.equals(env, ["-Xwarning-level=UNUSED:warning"], kotlinc_options_to_flags(_kopts(x_warning_level = {"UNUSED": "warning"})))
+
+    # value_to_flag dict path
+    asserts.equals(env, ["-Werror"], kotlinc_options_to_flags(_kopts(warn = "error")))
+    asserts.equals(env, ["-nowarn"], kotlinc_options_to_flags(_kopts(warn = "off")))
+    asserts.equals(env, ["-no-stdlib"], kotlinc_options_to_flags(_kopts(include_stdlibs = "none")))
+
+    # derive.info path (repeated_values_for)
+    asserts.equals(env, ["-Xsuppress-warning=SOME"], kotlinc_options_to_flags(_kopts(x_suppress_warning = ["SOME"])))
+
+    # defaults produce no flags; None provider is falsy
+    asserts.equals(env, [], kotlinc_options_to_flags(_kopts()))
+    asserts.true(env, not kotlinc_options_to_flags(None))
+
+    return unittest.end(env)
+
+kotlinc_flags_test = unittest.make(_kotlinc_flags_impl)
+
+def _javac_flags_impl(ctx):
+    env = unittest.begin(ctx)
+
+    # value_to_flag dict path
+    asserts.equals(env, ["--release 17"], javac_options_to_flags(struct(release = "17")))
+    asserts.equals(env, ["-Werror"], javac_options_to_flags(struct(warn = "error")))
+    asserts.equals(env, ["-nowarn"], javac_options_to_flags(struct(warn = "off")))
+
+    # derive.repeated_values_for path
+    asserts.equals(env, ["-Xlint:all", "-Xlint:cast"], javac_options_to_flags(struct(x_lint = ["all", "cast"])))
+    asserts.equals(env, ["--add-exports=java.base/sun.nio.ch"], javac_options_to_flags(struct(add_exports = ["java.base/sun.nio.ch"])))
+
+    # derive.format_key_value_for path
+    asserts.equals(env, ["-Akey=v"], javac_options_to_flags(struct(annotation_processor_options = {"key": "v"})))
+
+    # None provider is falsy
+    asserts.true(env, not javac_options_to_flags(None))
+
+    return unittest.end(env)
+
+javac_flags_test = unittest.make(_javac_flags_impl)
+
+def opts_test_suite(name):
+    unittest.suite(name, kotlinc_flags_test, javac_flags_test)