fix(web-api): uploadV2 alt text was never saved by Slack

.changeset/fix-upload-image-alt-text.md

@@ -0,0 +1,5 @@
+---
+"@slack/web-api": patch
+---
+
+fix: image alt text passed to `files.uploadV2` is now saved. Before, it was sent as `alt_text`, which Slack ignores. Deprecate `alt_text` in `files.getUploadURLExternal` arguments in favor of `alt_txt` ([#2788](https://github.com/slackapi/node-slack-sdk/issues/2788))

packages/web-api/src/WebClient.test.ts

@@ -1662,7 +1662,7 @@ describe('WebClient', () => {
 
     it('uploads multiple files', async () => {
       const scope = nock('https://slack.com')
-        .post('/api/files.getUploadURLExternal', { filename: 'test-png.png', length: 55292 })
+        .post('/api/files.getUploadURLExternal', { filename: 'test-png.png', length: 55292, alt_txt: 'A test image' })
         .reply(200, {
           ok: true,
           file_id: 'F0000000001',
@@ -1717,6 +1717,7 @@ describe('WebClient', () => {
           {
             file: fs.createReadStream('./test/fixtures/test-png.png'),
             filename: 'test-png.png',
+            alt_text: 'A test image',
           },
         ],
       });

packages/web-api/src/WebClient.ts

@@ -502,7 +502,7 @@ export class WebClient extends Methods {
         const options = {
           filename: upload.filename,
           length: upload.length,
-          alt_text: upload.alt_text,
+          alt_txt: upload.alt_text,
           snippet_type: upload.snippet_type,
         } as FilesGetUploadURLExternalArguments;
         if ('token' in upload) {

packages/web-api/src/types/request/files.ts

@@ -95,6 +95,8 @@ export interface FilesGetUploadURLExternalArguments extends TokenOverridable {
   /** @description Size in bytes of the file being uploaded. */
   length: number;
   /** @description Description of image for screen-reader. */
+  alt_txt?: string;
+  /** @deprecated Slack does not use this. Use `alt_txt`. */
   alt_text?: string;
   /** @description Syntax type of the snippet being uploaded. E.g. `python`. */
   snippet_type?: string;