refactor(dev-infra): move parseCommitMessagesForRange into the parse file (#39747)

When attempting to actually rely on `parseCommitMessagesForRange`, it became apparent
that the function really belongs in the parse file, rather than utils.

PR Close #39747

dev-infra/commit-message/parse.ts

@@ -6,6 +6,8 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {exec} from '../utils/shelljs';
+
 /** A parsed commit message. */
 export interface ParsedCommitMessage {
   header: string;
@@ -75,3 +77,30 @@ export function parseCommitMessage(commitMsg: string): ParsedCommitMessage {
     isRevert: REVERT_PREFIX_RE.test(commitMsg),
   };
 }
+
+/** Retrieve and parse each commit message in a provide range. */
+export function parseCommitMessagesForRange(range: string): ParsedCommitMessage[] {
+  /** A random number used as a split point in the git log result. */
+  const randomValueSeparator = `${Math.random()}`;
+  /**
+   * Custom git log format that provides the commit header and body, separated as expected with the
+   * custom separator as the trailing value.
+   */
+  const gitLogFormat = `%s%n%n%b${randomValueSeparator}`;
+
+  // Retrieve the commits in the provided range.
+  const result = exec(`git log --reverse --format=${gitLogFormat} ${range}`);
+  if (result.code) {
+    throw new Error(`Failed to get all commits in the range:\n  ${result.stderr}`);
+  }
+
+  return result
+      // Separate the commits from a single string into individual commits.
+      .split(randomValueSeparator)
+      // Remove extra space before and after each commit message.
+      .map(l => l.trim())
+      // Remove any superfluous lines which remain from the split.
+      .filter(line => !!line)
+      // Parse each commit message.
+      .map(commit => parseCommitMessage(commit));
+}