feat: use commit message template value as prefix

bin/reset_sandbox.sh

@@ -31,3 +31,7 @@ mkdir -p my_subdir
 mv bazz.js my_subdir
 # Delete.
 rm buzz.js
+
+# Commit template.
+git config commit.template _COMMIT_MESSAGE
+echo 'My commit prefix' >_COMMIT_MESSAGE

src/autofill.ts

@@ -4,6 +4,7 @@
 import * as vscode from "vscode";
 import { Repository } from "./api/git";
 import { getChanges } from "./git/cli";
+import { getCommitTemplateValue } from "./git/commitTemplate";
 import { getCommitMsg, setCommitMsg } from "./gitExtension";
 import { generateMsg } from "./prepareCommitMsg";
 
@@ -21,7 +22,11 @@ Try saving your files or stage any new (untracked) files.\
  *   2. Generate a message.
  *   3. Push message value to the commit message box.
  *
- * This is based on `prefixCommit` from the `git-prefix` extension.
+ * New functionality in the extension - the commit message file is read
+ * explicitly and the content used. Any content in the Git pane that was the
+ * "old message" is ignored then.
+ *
+ * This function is based on `prefixCommit` from the `git-prefix` extension.
  */
 export async function makeAndFillCommitMsg(repository: Repository) {
   const fileChanges = await getChanges();
@@ -39,5 +44,8 @@ export async function makeAndFillCommitMsg(repository: Repository) {
   const newMsg = generateMsg(fileChanges, oldMsg);
   console.debug("New message: ", newMsg);
 
+  const commitMessageValue = await getCommitTemplateValue();
+  console.debug({ commitMessageValue });
+
   setCommitMsg(repository, newMsg);
 }

src/cli.ts

@@ -18,6 +18,11 @@ import { generateMsg } from "./prepareCommitMsg";
  *
  * Expect multi-line text from `git diff-index` command as the first item in the shell arguments.
  *
+ * TODO: How to reverse the order so reading the value and using it as old message can appear _first_.
+ * Note that, unlike the VS Code extension, the CLI logic here cannot read an
+ * "old message" from the Git pane so that is not passed to `generateMsg`.
+ * Though maybe this can be modified using `commitTemplate.ts`.
+ *
  * Returns a suitable generated commit message as text.
  */
 function main(args: string[]) {

src/git/cli.ts

@@ -13,7 +13,11 @@ const exec = util.promisify(childProcess.exec);
 /**
  * Run a `git` subcommand with options and return output.
  */
-function _execute(cwd: string, subcommand: string, options: string[] = []) {
+export function execute(
+  cwd: string,
+  subcommand: string,
+  options: string[] = []
+) {
   const command = `git ${subcommand} ${options.join(" ")}`;
 
   const result = exec(command, { cwd });
@@ -44,11 +48,9 @@ async function _diffIndex(options: string[] = []): Promise<Array<string>> {
     ...options,
     "HEAD",
   ];
-  const { stdout, stderr } = await _execute(
-    getWorkspaceFolder(),
-    cmd,
-    fullOptions
-  );
+
+  const workspace = getWorkspaceFolder();
+  const { stdout, stderr } = await execute(workspace, cmd, fullOptions);
 
   if (stderr) {
     console.debug(`stderr for 'git ${cmd}' command:`, stderr);

src/git/commitTemplate.ts

@@ -0,0 +1,113 @@
+/**
+ * Commit template module.
+ *
+ * TODO: Move to docs and link there.
+ *
+ * Read the message from the a configured commit template file and use it as a
+ * prefix in the message.
+ *
+ * A commit template is built-in Git behavior to see a value for the start of
+ * each commit message. This is useful if you have a ticket number, project
+ * name, or similar to add at the start of each commit.
+ *
+ * Note that VS Code and Git CLI both automatically read from this file when
+ * generating a commit. However, the value is hard to use. There is behavior in
+ * this extension to move the old message to the end and enter a commit type
+ * prefix and commit message before it, but there is no way to know from the
+ * content of the message for sure whether the old message is a commit template
+ * value or just a hand-typed message.
+ *
+ * To avoid making an extra config value for the extension that one has to
+ * manage say in a Settings file or internal data, the approach is rather to use
+ * the existing commit template pattern in Git.
+ */
+import * as fs from "fs";
+import * as path from "path";
+import { getWorkspaceFolder } from "../workspace";
+import { execute } from "./cli";
+
+const CONFIG_SUBCOMMAND = "config";
+const COMMIT_TEMPLATE_IDENTIFIER = "commit.template";
+
+/**
+ * Get a value from the local Git config.
+ */
+export async function _getConfigValue(options: string[]) {
+  const workspace = getWorkspaceFolder();
+
+  const { stdout, stderr } = await execute(
+    workspace,
+    CONFIG_SUBCOMMAND,
+    options
+  );
+
+  if (stderr) {
+    console.debug(`stderr for 'git ${CONFIG_SUBCOMMAND}' command:`, stderr);
+  }
+
+  return stdout;
+}
+
+/**
+ * Get commit template path.
+ *
+ * Get the configured value for a commit template path if set.
+ */
+async function _getCommitTemplatePath() {
+  try {
+    const options = [COMMIT_TEMPLATE_IDENTIFIER];
+
+    return await _getConfigValue(options);
+  } catch (_e) {
+    console.error(_e);
+
+    return null;
+  }
+}
+
+/**
+ * Read a file.
+ *
+ * @param filePath Path to a file to read, relative to the workspace root.
+ *   e.g. "abc.txt" or "abc/def.txt"
+ */
+function _readFile(filePath: string) {
+  const workspace = getWorkspaceFolder();
+  const p = path.join(workspace, filePath);
+
+  let value;
+
+  try {
+    value = fs.readFileSync(p, "utf-8");
+  } catch (err: any) {
+    console.error(`Could not find template file: ${p}. ${err.toString()}`);
+
+    return null;
+  }
+
+  if (!value) {
+    return null;
+  }
+
+  console.debug(`Found file: ${p}. Found contents: ${value}`);
+
+  return value;
+}
+
+/**
+ * Get value of commit template file.
+ *
+ * @return Contents of a configured commit message template file, or `null` if
+ *   file is not configured or file is missing.
+ */
+export async function getCommitTemplateValue() {
+  const filePath = await _getCommitTemplatePath();
+
+  if (!filePath) {
+    console.error(`Could not read missing file: ${filePath}`);
+
+    return null;
+  }
+
+  return _readFile(filePath);
+}

src/prepareCommitMsg.ts

@@ -218,7 +218,7 @@ export function _generateMsgWithOld(lines: string[], oldMsg: string) {
  *
  * Old message could be the current commit message value in the UI box (which might be a commit
  * message template that VS Code has filled in), or a commit message template read from a file in
- * the case of a hook flow without VS Code.
+ * the case of a hook flow without VS Code (built-in Git functionality).
  *
  * @param lines A list of text values describing how files changes.
  */