backend-common: make .readTree required

packages/backend-common/src/reading/AzureUrlReader.ts

@@ -17,7 +17,7 @@
 import fetch from 'cross-fetch';
 import { Config } from '@backstage/config';
 import { NotFoundError } from '../errors';
-import { ReaderFactory, UrlReader } from './types';
+import { ReaderFactory, ReadTreeResponse, UrlReader } from './types';
 
 type Options = {
   // TODO: added here for future support, but we only allow dev.azure.com for now
@@ -86,6 +86,10 @@ export class AzureUrlReader implements UrlReader {
     throw new Error(message);
   }
 
+  readTree(): Promise<ReadTreeResponse> {
+    throw new Error('AzureUrlReader does not implement readTree');
+  }
+
   // Converts
   // from: https://dev.azure.com/{organization}/{project}/_git/reponame?path={path}&version=GB{commitOrBranch}&_a=contents
   // to:   https://dev.azure.com/{organization}/{project}/_apis/git/repositories/reponame/items?path={path}&version={commitOrBranch}

packages/backend-common/src/reading/BitbucketUrlReader.ts

@@ -18,7 +18,7 @@ import { Config } from '@backstage/config';
 import parseGitUri from 'git-url-parse';
 import fetch from 'cross-fetch';
 import { NotFoundError } from '../errors';
-import { ReaderFactory, UrlReader } from './types';
+import { ReaderFactory, ReadTreeResponse, UrlReader } from './types';
 
 const DEFAULT_BASE_URL = 'https://api.bitbucket.org/2.0';
 
@@ -209,6 +209,10 @@ export class BitbucketUrlReader implements UrlReader {
     throw new Error(message);
   }
 
+  readTree(): Promise<ReadTreeResponse> {
+    throw new Error('BitbucketUrlReader does not implement readTree');
+  }
+
   toString() {
     const { host, token, username, appPassword } = this.config;
     let authed = Boolean(token);

packages/backend-common/src/reading/FetchUrlReader.ts

@@ -16,7 +16,7 @@
 
 import fetch from 'cross-fetch';
 import { NotFoundError } from '../errors';
-import { UrlReader } from './types';
+import { ReadTreeResponse, UrlReader } from './types';
 
 /**
  * A UrlReader that does a plain fetch of the URL.
@@ -41,6 +41,10 @@ export class FetchUrlReader implements UrlReader {
     throw new Error(message);
   }
 
+  readTree(): Promise<ReadTreeResponse> {
+    throw new Error('FetchUrlReader does not implement readTree');
+  }
+
   toString() {
     return 'fetch{}';
   }

packages/backend-common/src/reading/GitlabUrlReader.ts

@@ -17,7 +17,7 @@
 import fetch from 'cross-fetch';
 import { Config } from '@backstage/config';
 import { NotFoundError } from '../errors';
-import { ReaderFactory, UrlReader } from './types';
+import { ReaderFactory, ReadTreeResponse, UrlReader } from './types';
 
 type Options = {
   host: string;
@@ -87,6 +87,10 @@ export class GitlabUrlReader implements UrlReader {
     throw new Error(message);
   }
 
+  readTree(): Promise<ReadTreeResponse> {
+    throw new Error('GitlabUrlReader does not implement readTree');
+  }
+
   // Converts
   // from: https://gitlab.example.com/a/b/blob/master/c.yaml
   // to:   https://gitlab.example.com/a/b/raw/master/c.yaml

packages/backend-common/src/reading/UrlReaderPredicateMux.ts

@@ -66,19 +66,12 @@ export class UrlReaderPredicateMux implements UrlReader {
 
     for (const { predicate, reader } of this.readers) {
       if (predicate(parsed)) {
-        if (reader.readTree) return reader.readTree(repoUrl, options);
-        throw new Error(
-          `Trying to call readTree on UrlReader which does not support the feature.`,
-        );
+        return reader.readTree(repoUrl, options);
       }
     }
 
     if (this.fallback) {
-      if (this.fallback.readTree)
-        return this.fallback.readTree(repoUrl, options);
-      throw new Error(
-        `Trying to call readTree on UrlReader which does not support the feature.`,
-      );
+      return this.fallback.readTree(repoUrl, options);
     }
 
     throw new Error(`No reader found that could handle '${repoUrl}'`);

packages/backend-common/src/reading/types.ts

@@ -28,7 +28,7 @@ export type ReadTreeOptions = {
  */
 export type UrlReader = {
   read(url: string): Promise<Buffer>;
-  readTree?(url: string, options?: ReadTreeOptions): Promise<ReadTreeResponse>;
+  readTree(url: string, options?: ReadTreeOptions): Promise<ReadTreeResponse>;
 };
 
 export type UrlReaderPredicateTuple = {