feat: add version:info command to display changelog entries

Add new version:info command that displays changelog information for
specific CLI versions or the most recent version.

Features:
- Takes an optional version argument (e.g., '11.0.0', '10.17.0')
- When no version is provided, displays the most recent changelog entry
- Smart summary extraction: if the version entry has a Summary section
  as the first content, only shows the summary with a link to the full
  changelog
- Handles both ## and # markdown headers for version entries
- Provides helpful error messages for non-existent versions

Examples:
  heroku version:info              # Show most recent version
  heroku version:info 11.0.0       # Show specific version
  heroku version:info 10.17.0      # Show older version

Includes comprehensive unit tests (10 tests) covering:
- Summary extraction logic
- Most recent entry extraction
- Specific version lookup
- Edge cases (missing versions, empty changelog, etc.)

Author: eablack

src/commands/version/info.ts

@@ -0,0 +1,192 @@
+import {Args, Command, ux} from '@oclif/core'
+import {readFile} from 'node:fs/promises'
+import {join} from 'node:path'
+import {fileURLToPath} from 'node:url'
+
+export default class VersionInfo extends Command {
+  static args = {
+    version: Args.string({
+      description: 'version number to look up (e.g., 11.0.0, 10.17.0)',
+      required: false,
+    }),
+  }
+
+  static description = 'display changelog information for a specific CLI version'
+
+  static examples = [
+    '<%= config.bin %> <%= command.id %>',
+    '<%= config.bin %> <%= command.id %> 11.0.0',
+    '<%= config.bin %> <%= command.id %> 10.17.0',
+  ]
+
+  async run() {
+    const {args} = await this.parse(VersionInfo)
+    const {version} = args
+
+    try {
+      // Find the CHANGELOG.md file relative to the CLI installation
+      const __dirname = fileURLToPath(new URL('.', import.meta.url))
+      const changelogPath = join(__dirname, '..', '..', '..', 'CHANGELOG.md')
+
+      const changelogContent = await readFile(changelogPath, 'utf8')
+
+      let entry: string | null
+
+      if (version) {
+        // Extract the entry for the specified version
+        entry = this.extractVersionEntry(changelogContent, version)
+
+        if (!entry) {
+          ux.error(`Version ${version} not found in CHANGELOG.md`, {exit: 1})
+        }
+      } else {
+        // If no version specified, get the most recent entry
+        entry = this.extractMostRecentEntry(changelogContent)
+
+        if (!entry) {
+          ux.error('No version entries found in CHANGELOG.md', {exit: 1})
+        }
+      }
+
+      // If the entry has a Summary section as the first content, only show that
+      const summaryOnly = this.extractSummaryIfFirst(entry)
+      if (summaryOnly) {
+        ux.stdout(summaryOnly)
+        ux.stdout('')
+        ux.stdout('For the full changelog, visit: https://github.com/heroku/cli/blob/main/CHANGELOG.md')
+      } else {
+        ux.stdout(entry)
+      }
+    } catch (error: any) {
+      if (error.code === 'ENOENT') {
+        ux.error('CHANGELOG.md not found', {exit: 1})
+      }
+
+      throw error
+    }
+  }
+
+  private extractSummaryIfFirst(entry: string): string | null {
+    const lines = entry.split('\n')
+    let summaryStartIndex = -1
+    let summaryEndIndex = -1
+
+    // Find if "### Summary" appears early in the entry (within first few lines after header)
+    for (let i = 0; i < Math.min(5, lines.length); i++) {
+      if (lines[i].trim() === '### Summary') {
+        summaryStartIndex = i
+        break
+      }
+    }
+
+    if (summaryStartIndex === -1) {
+      return null
+    }
+
+    // Find the end of the summary section (next ### header or end of entry)
+    for (let i = summaryStartIndex + 1; i < lines.length; i++) {
+      if (lines[i].match(/^###\s+/)) {
+        summaryEndIndex = i
+        break
+      }
+    }
+
+    if (summaryEndIndex === -1) {
+      // Summary goes to the end
+      summaryEndIndex = lines.length
+    }
+
+    // Extract header + summary section
+    const header = lines.slice(0, summaryStartIndex).join('\n')
+    const summary = lines.slice(summaryStartIndex, summaryEndIndex).join('\n')
+
+    return (header + '\n' + summary).trim()
+  }
+
+  private extractMostRecentEntry(changelog: string): string | null {
+    const lines = changelog.split('\n')
+    let startIndex = -1
+    let endIndex = -1
+
+    // Find the first version header (most recent)
+    for (const [i, line] of lines.entries()) {
+      const match = line.match(/^##? \[([^\]]+)\]/)
+      if (match) {
+        startIndex = i
+        break
+      }
+    }
+
+    if (startIndex === -1) {
+      return null
+    }
+
+    // Find the end of the version entry (start of next version or end of file)
+    for (let i = startIndex + 1; i < lines.length; i++) {
+      if (lines[i].match(/^##? \[/)) {
+        endIndex = i
+        break
+      }
+    }
+
+    if (endIndex === -1) {
+      endIndex = lines.length
+    }
+
+    // Extract the entry
+    const entry = lines.slice(startIndex, endIndex).join('\n').trim()
+
+    return entry
+  }
+
+  private extractVersionEntry(changelog: string, version: string): string | null {
+    // Handle different version formats (with or without 'v' prefix)
+    const versionPattern = version.startsWith('v') ? version : `v${version}`
+    const versionWithoutV = version.startsWith('v') ? version.slice(1) : version
+
+    // Split the changelog by version headers
+    // Headers can be like:
+    // ## [11.0.0-beta.0](link) (date)
+    // # [10.17.0](link) (date)
+    const versionHeaderRegex = /^##? \[([^\]]+)\]/gm
+
+    const lines = changelog.split('\n')
+    let startIndex = -1
+    let endIndex = -1
+    let foundVersion = ''
+
+    // Find the start of the version entry
+    for (const [i, line] of lines.entries()) {
+      const match = line.match(/^##? \[([^\]]+)\]/)
+      if (match) {
+        const versionInHeader = match[1]
+        if (versionInHeader === versionWithoutV || versionInHeader === versionPattern) {
+          startIndex = i
+          foundVersion = versionInHeader
+          break
+        }
+      }
+    }
+
+    if (startIndex === -1) {
+      return null
+    }
+
+    // Find the end of the version entry (start of next version or end of file)
+    for (let i = startIndex + 1; i < lines.length; i++) {
+      if (lines[i].match(/^##? \[/)) {
+        endIndex = i
+        break
+      }
+    }
+
+    if (endIndex === -1) {
+      endIndex = lines.length
+    }
+
+    // Extract the entry
+    const entry = lines.slice(startIndex, endIndex).join('\n').trim()
+
+    return entry
+  }
+}