Betterer: Add our own regexp matcher (#79448)

* Add betterer rule for gf-form

* Betterer: Write generic regexp matcher

* Add space

* Update lockfile

* Update comments

* Add comment with notice

.betterer.ts

@@ -12,12 +12,18 @@ const eslintPathsToIgnore = [
   'public/app/plugins/panel/graph', // will be removed alongside angular
 ];
 
+// Avoid using functions that report the position of the issues, as this causes a lot of merge conflicts
 export default {
   'better eslint': () =>
     countEslintErrors()
       .include('**/*.{ts,tsx}')
       .exclude(new RegExp(eslintPathsToIgnore.join('|'))),
   'no undocumented stories': () => countUndocumentedStories().include('**/!(*.internal).story.tsx'),
+  'no gf-form usage': () =>
+    regexp(
+      /gf-form/gm,
+      'gf-form usage has been deprecated. Use a component from @grafana/ui or custom CSS instead.'
+    ).include('**/*.{ts,tsx,html}'),
 };
 
 function countUndocumentedStories() {
@@ -38,6 +44,28 @@ function countUndocumentedStories() {
   });
 }
 
+/**
+ *  Generic regexp pattern matcher, similar to @betterer/regexp.
+ *  The only difference is that the positions of the errors are not reported, as this may cause a lot of merge conflicts.
+ */
+function regexp(pattern: RegExp, issueMessage: string) {
+  return new BettererFileTest(async (filePaths, fileTestResult) => {
+    await Promise.all(
+      filePaths.map(async (filePath) => {
+        const fileText = await fs.readFile(filePath, 'utf8');
+        const matches = fileText.match(pattern);
+        if (matches) {
+          // File contents doesn't matter, since we're not reporting the position
+          const file = fileTestResult.addFile(filePath, '');
+          matches.forEach(() => {
+            file.addIssue(0, 0, issueMessage);
+          });
+        }
+      })
+    );
+  });
+}
+
 function countEslintErrors() {
   return new BettererFileTest(async (filePaths, fileTestResult, resolver) => {
     const { baseDirectory } = resolver;