Continued refactoring to simplify code

Author: kristoferbaxter

src/options.ts

@@ -18,7 +18,7 @@ import { Transform } from './types';
 import { ModuleFormat, OutputOptions } from 'rollup';
 import { CompileOptions } from 'google-closure-compiler';
 import { sync } from 'temp-write';
-import { log, logSource } from './debug';
+import { log } from './debug';
 
 export const ERROR_WARNINGS_ENABLED_LANGUAGE_OUT_UNSPECIFIED =
   'Providing the warning_level=VERBOSE compile option also requires a valid language_out compile option.';
@@ -39,15 +39,16 @@ export const isESMFormat = (format?: ModuleFormat): boolean => {
  * Throw Errors if compile options will result in unexpected behaviour.
  * @param compileOptions
  */
-const validateCompileOptions = (compileOptions: CompileOptions): void => {
+function validateCompileOptions(compileOptions: CompileOptions): void {
   if ('warning_level' in compileOptions && compileOptions.warning_level === 'VERBOSE') {
     if (!('language_out' in compileOptions)) {
       throw new Error(ERROR_WARNINGS_ENABLED_LANGUAGE_OUT_UNSPECIFIED);
-    } else if ('language_out' in compileOptions && compileOptions.language_out === 'NO_TRANSPILE') {
+    }
+    if (compileOptions.language_out === 'NO_TRANSPILE') {
       throw new Error(ERROR_WARNINGS_ENABLED_LANGUAGE_OUT_INVALID);
     }
   }
-};
+}
 
 /**
  * Generate default Closure Compiler CompileOptions an author can override if they wish.
@@ -67,30 +68,20 @@ export const defaults = (
   // - When Rollup output is set to "es|esm" it is expected the code will live in a ES Module,
   // so safely be more aggressive in minification.
 
-  const externs = transformers
-    ? transformers
-        .map(transform => {
-          const extern = transform.extern(options);
-          return extern !== '' ? sync(extern) : false;
-        })
-        .filter(Boolean)
-        .concat(providedExterns)
-    : providedExterns.length > 0
-    ? providedExterns
-    : '';
-
-  if (typeof externs === 'string' && externs !== '') {
-    logSource('externs', externs);
-  } else if (Array.isArray(externs)) {
-    log('externs', externs);
+  const transformerExterns: Array<string> = [];
+  for (const transform of transformers || []) {
+    const extern = transform.extern(options);
+    if (extern !== null) {
+      transformerExterns.push(sync(extern));
+    }
   }
 
   return {
     language_out: 'NO_TRANSPILE',
     assume_function_wrapper: isESMFormat(options.format),
     warning_level: 'QUIET',
     module_resolution: 'NODE',
-    externs,
+    externs: transformerExterns.concat(providedExterns),
   };
 };
 

src/transformers/cjs.ts

@@ -38,11 +38,11 @@ var exports;`;
 export default class CJSTransform extends Transform {
   public name = 'CJSTransform';
 
-  public extern(options: OutputOptions): string {
+  public extern(options: OutputOptions): string | null {
     if (options.format === 'cjs') {
       return HEADER;
     }
 
-    return '';
+    return null;
   }
 }

src/transformers/exports.ts

@@ -102,7 +102,7 @@ export default class ExportTransform extends Transform implements TransformInter
     });
   }
 
-  public extern(): string {
+  public extern(): string | null {
     if (Array.from(this.originalExports.keys()).length > 0) {
       let output = EXTERN_OVERVIEW;
 
@@ -116,7 +116,7 @@ export default class ExportTransform extends Transform implements TransformInter
       return output;
     }
 
-    return '';
+    return null;
   }
 
   /**

src/transformers/iife.ts

@@ -33,11 +33,11 @@ const HEADER = `/**
 export default class IifeTransform extends Transform {
   public name = 'IifeTransform';
 
-  public extern(options: OutputOptions): string {
+  public extern(options: OutputOptions): string | null {
     if (options.format === 'iife' && options.name) {
       return HEADER + `window['${options.name}'] = ${options.name};\n`;
     }
 
-    return '';
+    return null;
   }
 }

src/transformers/imports.ts

@@ -66,12 +66,13 @@ export default class ImportTransform extends Transform {
    * Otherwise, advanced mode compilation will fail since the reference is unknown.
    * @return string representing content of generated extern.
    */
-  public extern(): string {
-    let extern = HEADER;
+  public extern(): string | null {
+    let extern: string = HEADER;
+
     if (this.importedExternalsLocalNames.length > 0) {
-      this.importedExternalsLocalNames.forEach(name => {
+      for (const name of this.importedExternalsLocalNames) {
         extern += `function ${name}(){};\n`;
-      });
+      }
     }
 
     if (this.dynamicImportPresent) {
@@ -84,7 +85,7 @@ function ${DYNAMIC_IMPORT_REPLACEMENT}(path) { return Promise.resolve(path) };
 window['${DYNAMIC_IMPORT_REPLACEMENT}'] = ${DYNAMIC_IMPORT_REPLACEMENT};`;
     }
 
-    return extern;
+    return extern === HEADER ? null : extern;
   }
 
   /**

src/types.ts

@@ -62,7 +62,7 @@ export interface ExportDetails {
 export type TransformMethod = (code: string) => Promise<TransformSourceDescription>;
 export interface TransformInterface {
   name: string;
-  extern: (options: OutputOptions) => string;
+  extern: (options: OutputOptions) => string | null;
   preCompilation: TransformMethod;
   postCompilation: TransformMethod;
 }
@@ -77,8 +77,8 @@ export class Transform implements TransformInterface {
     this.inputOptions = inputOptions;
   }
 
-  public extern(options: OutputOptions): string {
-    return '';
+  public extern(options: OutputOptions): string | null {
+    return null;
   }
 
   public async preCompilation(code: string): Promise<TransformSourceDescription> {