fix: Detect theme component CSS changes even without theme.json (#23452) (#23457)

themeShadowDOMStylesheetsChanged only scanned for components/ folders
in themes discovered via theme.json. Themes without a theme.json
(but with a components/ directory) were silently skipped, so the
dev bundle was never rebuilt to include their component styles.

Always include the main theme name when scanning for components/
folders, regardless of whether theme.json exists.

Fixes #23438

Co-authored-by: Artur Signell <artur@vaadin.com>

Author: vaadin-bot

flow-server/src/main/java/com/vaadin/flow/server/frontend/ThemeValidationUtil.java

@@ -25,6 +25,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -173,12 +174,18 @@ public static boolean themeShadowDOMStylesheetsChanged(Options options,
                 .map(ThemeDefinition::getName).filter(name -> !name.isBlank())
                 .map(themeName -> {
                     Map<String, JsonNode> themeJsonContents = new HashMap<>();
-                    ThemeUtils.getThemeJson(themeName, frontendDirectory)
-                            .ifPresent(
-                                    themeJson -> collectThemeJsonContentsInFrontend(
-                                            options, themeJsonContents,
-                                            themeName, themeJson));
-                    return themeJsonContents.keySet().stream()
+                    Optional<JsonNode> themeJson = ThemeUtils
+                            .getThemeJson(themeName, frontendDirectory);
+                    themeJson.ifPresent(
+                            json -> collectThemeJsonContentsInFrontend(options,
+                                    themeJsonContents, themeName, json));
+                    // Always include the main theme itself, even
+                    // without theme.json, so its components/ folder
+                    // is checked
+                    Set<String> themeNames = new HashSet<>(
+                            themeJsonContents.keySet());
+                    themeNames.add(themeName);
+                    return themeNames.stream()
                             .map(name -> ThemeUtils
                                     .getThemeFolder(frontendDirectory, name))
                             .map(dir -> new File(dir, "components"))

flow-server/src/test/java/com/vaadin/flow/server/frontend/BundleValidationTest.java

@@ -1795,6 +1795,39 @@ public void projectParentInJarThemeComponentsCSS_removedFromProject_bundleRebuil
                 needsBuild);
     }
 
+    @Test
+    public void projectThemeComponentsCSS_noThemeJson_bundleRebuild()
+            throws IOException {
+        // Theme has components/ folder with CSS but no theme.json
+        String cssTemplate = "[part=\"input-field\"]{background: %s; }";
+        createPackageJsonStub(BLANK_PACKAGE_JSON_WITH_HASH);
+
+        // Create components CSS file without creating theme.json
+        String themeLocation = "themes/my-theme/components/";
+        File stylesheetFile = new File(temporaryFolder.getRoot(),
+                DEFAULT_FRONTEND_DIR + themeLocation + "vaadin-text-field.css");
+        FileUtils.forceMkdir(stylesheetFile.getParentFile());
+        FileUtils.write(stylesheetFile, String.format(cssTemplate, "blue"),
+                StandardCharsets.UTF_8);
+
+        final FrontendDependenciesScanner depScanner = Mockito
+                .mock(FrontendDependenciesScanner.class);
+        final ThemeDefinition themeDefinition = Mockito
+                .mock(ThemeDefinition.class);
+        Mockito.when(themeDefinition.getName()).thenReturn("my-theme");
+        Mockito.when(depScanner.getThemeDefinition())
+                .thenReturn(themeDefinition);
+
+        ObjectNode stats = getBasicStats();
+        setupFrontendUtilsMock(stats);
+
+        boolean needsBuild = BundleValidationUtil.needsBuild(options,
+                depScanner, mode);
+        Assert.assertTrue(
+                "Should rebuild when theme has components CSS but no theme.json",
+                needsBuild);
+    }
+
     @Test
     public void indexTsAdded_rebuildRequired() throws IOException {
         createPackageJsonStub(BLANK_PACKAGE_JSON_WITH_HASH);