only show no-undef errors for templates in gts files

lib/preprocessors/glimmer.js

@@ -8,6 +8,7 @@ const util = require('ember-template-imports/src/util');
 
 const TRANSFORM_CACHE = new Map();
 const TEXT_CACHE = new Map();
+const RULE_CACHE = new Map();
 
 function arrayEq(arr1, arr2) {
   return arr1.length === arr2.length && arr1.every((val, idx) => val === arr2[idx]);
@@ -86,10 +87,33 @@ function gjs(text, filename) {
   //
   // We need to disable all of eslint around this "scope" return
   // value and allow-list the rules that check for undefined identifiers
+  const groups = [];
   const transformed = preprocessed.output;
+  let isInsideTemplate = false;
+  for (const [index, line] of transformed.split('\n').entries()) {
+    const lineHasOpeningTag = openingTemplateTagRegex.test(line);
+    const lineHasClosingTag = closingTemplateTagRegex.test(line);
+
+    if (lineHasOpeningTag) {
+      isInsideTemplate = true;
+      groups.push({
+        startLine: index + 1,
+        endLine: index + 1,
+        startColumn: line.search(openingTemplateTagRegex) + 1,
+      });
+    }
+
+    if (lineHasClosingTag && isInsideTemplate) {
+      isInsideTemplate = false;
+      const match = line.match(closingTemplateTagRegex);
+      groups.slice(-1)[0].endLine = index + 1;
+      groups.slice(-1)[0].endColumn = match.index + match[0].length + 1;
+    }
+  }
 
   TRANSFORM_CACHE.set(filename, transformed);
   TEXT_CACHE.set(filename, text);
+  RULE_CACHE.set(filename, groups);
 
   return [
     {
@@ -108,6 +132,7 @@ function gjs(text, filename) {
 function mapRange(messages, filename) {
   const transformed = TRANSFORM_CACHE.get(filename);
   const original = TEXT_CACHE.get(filename);
+  const groups = RULE_CACHE.get(filename);
   const flattened = messages.flat();
 
   if (!transformed) {
@@ -135,7 +160,29 @@ function mapRange(messages, filename) {
     );
   }
 
-  return flattened.map((message) => {
+  const filtered = flattened.filter(
+    (it) =>
+      it.ruleId === 'no-undef' ||
+      groups.some(
+        (
+          g // include if message wraps group
+        ) =>
+          g.startLine >= it.line &&
+          g.startColumn >= it.column &&
+          g.endLine <= it.endLine &&
+          g.endColumn <= it.endColumn
+      ) ||
+      !groups.some(
+        (
+          g // exclude if message is within group (also when it ends on next line, column 1)
+        ) =>
+          g.startLine <= it.line &&
+          g.startColumn <= it.column &&
+          (g.endLine >= it.endLine || (it.endLine === g.endLine + 1 && it.endColumn === 1))
+      )
+  );
+
+  return filtered.map((message) => {
     // 1. handle eslint diagnostics on single lines.
     if (message.line === message.endLine) {
       const originalLine = originalLines[message.line - 1];