Fix LightningCSS.bundle to report its exports and warnings

README.md

@@ -62,6 +62,18 @@ LightningCSS.transform(".a { color: lab(50% 40 59) }", targets: { chrome: 80 },
 LightningCSS.bundle("app/assets/stylesheets/application.css", minify: true).code
 ```
 
+It answers the same result a transform does. Every warning names the file it came from, and compiling as a CSS module renames the names in every file it read while exporting the ones the entry wrote. A file it imported is hashed on its own, so its names never collide with the entry's.
+
+```ruby
+result = LightningCSS.bundle("app/assets/stylesheets/application.css", css_modules: true)
+
+result.exports
+#=> {"application" => "_8Z4fiW_application"}
+
+result.warnings.first
+#=> "'deep' is not recognized as a valid pseudo-class. ... at app/assets/stylesheets/layout.css:0:9"
+```
+
 #### CSS modules
 
 Compiling as a CSS module renames every class, id, `@keyframes`, and custom identifier, and reports what each name became.

rust/src/lib.rs

@@ -151,13 +151,16 @@ fn bundle_source(path: &str, options: &TransformOptions) -> Result<TransformResu
     None => None,
   };
 
+  let provider = FileProvider::new();
+  let collected = Arc::new(RwLock::new(Vec::new()));
+
   let parser_options = ParserOptions {
     css_modules,
     error_recovery: options.error_recovery,
+    warnings: Some(collected.clone()),
     ..ParserOptions::default()
   };
 
-  let provider = FileProvider::new();
   let mut bundler = Bundler::new(&provider, None, parser_options);
 
   let mut stylesheet = bundler
@@ -191,10 +194,22 @@ fn bundle_source(path: &str, options: &TransformOptions) -> Result<TransformResu
     })
     .map_err(|error| format!("Failed to print: {error}"))?;
 
+  let exports = printed.exports.map(|exports| {
+    exports
+      .into_iter()
+      .map(|(local, export)| (local, export.name))
+      .collect::<HashMap<String, String>>()
+  });
+
+  let warnings = collected
+    .read()
+    .map(|warnings| warnings.iter().map(|warning| warning.to_string()).collect())
+    .unwrap_or_default();
+
   Ok(TransformResult {
     code: printed.code,
-    exports: None,
-    warnings: Vec::new(),
+    exports,
+    warnings,
   })
 }
 

test/fixtures/bundle/nested/warned.css

@@ -0,0 +1 @@
+.a:deep(.b) { color: red; }

test/fixtures/bundle/warned.css

@@ -0,0 +1,3 @@
+@import "nested/warned.css";
+
+.warned { color: var(--brand); }

test/lightningcss/bundle_test.rb

@@ -6,6 +6,9 @@ module LightningCSS
   class BundleTest < Minitest::Spec
     ENTRY = File.expand_path("../fixtures/bundle/entry.css", __dir__)
     MISSING = File.expand_path("../fixtures/bundle/missing.css", __dir__)
+    WARNED = File.expand_path("../fixtures/bundle/warned.css", __dir__)
+    IMPORTED = File.expand_path("../fixtures/bundle/nested/warned.css", __dir__)
+    WARNING = "'deep' is not recognized as a valid pseudo-class. Did you mean '::deep' (pseudo-element) or is this a typo? at #{IMPORTED}:0:9".freeze
 
     test "resolves the imports a stylesheet was written with, in the order it imported them" do
       code = LightningCSS.bundle(ENTRY, minify: true).code
@@ -34,5 +37,45 @@ class BundleTest < Minitest::Spec
 
       assert_equal ":root{--brand:red}.layout{display:grid}.entry{color:var(--brand)}", code
     end
+
+    test "renames every name it bundled, and reports the ones the entry wrote" do
+      result = LightningCSS.bundle(ENTRY, css_modules: { pattern: "bundled-[local]" }, minify: true)
+
+      assert_equal ":root{--brand:red}.bundled-layout{display:grid}.bundled-entry{color:var(--brand)}", result.code
+      assert_equal({ "entry" => "bundled-entry" }, result.exports)
+    end
+
+    test "hashes every file it bundled on its own, so two of them never collide" do
+      code = LightningCSS.bundle(ENTRY, css_modules: true, minify: true).code
+
+      entry = code[/\.(\w+)_entry\{/, 1]
+      layout = code[/\.(\w+)_layout\{/, 1]
+
+      refute_nil entry
+      refute_nil layout
+      refute_equal entry, layout
+    end
+
+    test "reports no exports when it was not asked to compile a CSS module" do
+      assert_nil LightningCSS.bundle(ENTRY, minify: true).exports
+    end
+
+    test "reports what it kept but did not understand, and which file wrote it" do
+      result = LightningCSS.bundle(WARNED, minify: true)
+
+      assert_equal [WARNING], result.warnings
+      assert_predicate result, :warnings?
+    end
+
+    test "keeps the rule it warned about" do
+      assert_includes LightningCSS.bundle(WARNED, minify: true).code, ".a:deep(.b){color:red}"
+    end
+
+    test "reports none for a bundle it fully understood" do
+      result = LightningCSS.bundle(ENTRY, minify: true)
+
+      assert_empty result.warnings
+      refute_predicate result, :warnings?
+    end
   end
 end