[FIX] processors/libraryLessGenerator: Don't throw in case of import errors

To be compatible with the previous behavior (Maven), the processor
should not throw an error in case an import can't be handled.
Instead the error is logged and a comment is added to the resulting
library.less file.

Author: matz3

lib/processors/libraryLessGenerator.js

@@ -8,6 +8,14 @@ const IMPORT_PATTERN = /@import .*"(.*)";/g;
 const BASE_LESS_PATTERN = /^\/resources\/sap\/ui\/core\/themes\/([^/]+)\/base\.less$/;
 const GLOBAL_LESS_PATTERN = /^\/resources\/sap\/ui\/core\/themes\/([^/]+)\/global\.less$/;
 
+class ImportError extends Error {
+	constructor(message) {
+		super();
+		this.name = "ImportError";
+		this.message = message;
+	}
+}
+
 class LibraryLessGenerator {
 	constructor({fs}) {
 		const readFile = promisify(fs.readFile);
@@ -33,7 +41,17 @@ class LibraryLessGenerator {
 		const replacements = await Promise.all(imports.map(async (importMatch) => {
 			const baseDir = posixPath.dirname(filePath);
 			const resolvedFilePath = posixPath.resolve(baseDir, importMatch.path);
-			importMatch.content = await this.resolveLessImport(importMatch.path, resolvedFilePath, baseDir);
+			try {
+				importMatch.content = await this.resolveLessImport(importMatch.path, resolvedFilePath, baseDir);
+			} catch (error) {
+				if (error instanceof ImportError) {
+					// Add message of import errors after the import statements
+					// Currently those errors should not break the build (see comments in resolveLessImport)
+					importMatch.content = importMatch.fullMatch + ` /* ${error} */`;
+				} else {
+					throw error;
+				}
+			}
 			return importMatch;
 		}));
 
@@ -78,19 +96,26 @@ class LibraryLessGenerator {
 		}
 
 		/*
-		 * Throw error in case of files which are not in the same directory as the current file because
+		 * Log error in case of files which are not in the same directory as the current file because
 		 * inlining them would break relative URLs.
-		 * Keeping the import is also not possible since only "library.less" and "global.less" are
+		 * A possible solution would be to rewrite relative URLs when inlining the content.
+		 *
+		 * Keeping the import will cause errors since only "library.less" and "global.less" are
 		 * configured to be available to the Theme Designer (.theming generated in generateThemeDesignerResources).
+		 * However, the previous implementation did not break the build.
+		 * In many cases the library.less file is currently not relevant so breaking the build would cause
+		 * unnecessary issues.
 		 *
-		 * A possible solution would be to rewrite relative URLs when inlining the content.
 		 */
 		const relativeFilePath = posixPath.relative(baseDir, resolvedFilePath);
 		if (relativeFilePath.includes(posixPath.sep)) {
-			throw new Error(
-				`libraryLessGenerator: Unsupported import of file '${resolvedFilePath}'. ` +
-				`Stylesheets must be located in the theme directory '${baseDir}' (no sub-directories)`
+			log.error(
+				`Could not inline import '${resolvedFilePath}' outside of theme directory '${baseDir}'. ` +
+				`Stylesheets must be located in the theme directory (no sub-directories). ` +
+				`The generated '${baseDir}/library.less' will cause errors when compiled with the Theme Designer.`
 			);
+			// Throw error to be added as comment to the import statement
+			throw new ImportError("Could not inline import outside of theme directory");
 		}
 
 		let importedFileContent;
@@ -119,6 +144,7 @@ class LibraryLessGenerator {
 		while ((match = IMPORT_PATTERN.exec(fileContent)) !== null) {
 			imports.push({
 				path: match[1],
+				fullMatch: match[0],
 				matchStart: match.index,
 				matchLength: match[0].length
 			});