fix: support .js inputs without out_dir

examples/allow_js/BUILD.bazel

@@ -0,0 +1,19 @@
+"""Simple use case for swc: transpiling .js using the `swc` rule, similar to tsc with 'allowJs'
+"""
+
+load("@aspect_bazel_lib//lib:write_source_files.bzl", "write_source_files")
+load("@aspect_rules_swc//swc:defs.bzl", "swc")
+
+# Runs `swc in.js > ../../bazel-bin/examples/js_outs/in.js`
+swc(
+    name = "compile",
+    srcs = ["in.js"],
+)
+
+# Assert that the output of "compile" rule matches the expected file.
+write_source_files(
+    name = "test",
+    # There is no pre-declared output of the "compile" rule because the input is .js
+    # so the the target name is used instead of output file.
+    files = {"expected.js": ":compile"},
+)

examples/allow_js/expected.js

@@ -0,0 +1 @@
+export var a = "simple";

examples/allow_js/in.js

@@ -0,0 +1 @@
+export const a = "simple";

swc/private/swc.bzl

@@ -141,18 +141,10 @@ def _calculate_js_out(src, out_dir, root_dir, js_outs = []):
     return js_out
 
 def _calculate_js_outs(srcs, out_dir, root_dir):
-    if out_dir == None:
-        js_srcs = []
-        for src in srcs:
-            if src.endswith(".js"):
-                js_srcs.append(src)
-        if len(js_srcs) > 0:
-            fail("Detected swc rule with srcs=[{}, ...] and out_dir=None. Please set out_dir when compiling .js files.".format(", ".join(js_srcs[:3])))
-
     out = []
     for f in srcs:
         js_out = _calculate_js_out(f, out_dir, root_dir)
-        if js_out:
+        if js_out and js_out != f:
             out.append(js_out)
     return out