Fix source checking when parsing {{~!~}} and the like.

packages/@glimmer/compiler/test/compiler-test.ts

@@ -317,6 +317,8 @@ test('top-level comments', `<!-- {{foo}} -->`, c` {{foo}} `);
 
 test('handlebars comments', `<div>{{! Better not break! }}content</div>`, ['<div>', [s`content`]]);
 
+test('handlebars comments with whitespace removal', '<div>  {{~! some comment ~}}  content</div>', ['<div>', [s`content`]]);
+
 test('namespaced attribute', `<svg xlink:title='svg-title'>content</svg>`, [
   '<svg>',
   { 'xlink:title': s`svg-title` },

packages/@glimmer/syntax/lib/v2/normalize.ts

@@ -353,12 +353,18 @@ class StatementNormalizer {
     let loc = this.block.loc(node.loc);
     let textLoc: SourceSpan;
 
-    if (loc.asString().slice(0, 5) === '{{!--') {
-      textLoc = loc.slice({ skipStart: 5, skipEnd: 4 });
-    } else {
-      textLoc = loc.slice({ skipStart: 3, skipEnd: 2 });
+    let locStr = loc.asString();
+
+    let skipStart = locStr.startsWith('{{~') ? 4 : 3;
+    let skipEnd = locStr.endsWith('~}}') ? 3 : 2;
+
+    if (locStr.slice(skipStart-1).startsWith('!--')) {
+      skipStart += 2;
+      skipEnd += 2;
     }
 
+    textLoc = loc.slice({ skipStart, skipEnd });
+
     return new ASTv2.GlimmerComment({
       loc,
       text: textLoc.toSlice(node.value),

packages/@glimmer/syntax/test/parser-node-test.ts

@@ -524,6 +524,14 @@ test('a Handlebars comment', function () {
   );
 });
 
+test('a Handlebars comment with whitespace removal', function () {
+  let t = 'before {{~! some comment ~}} after';
+  astEqual(
+    t,
+    b.program([b.text('before'), b.mustacheComment(' some comment '), b.text('after')])
+  );
+});
+
 test('a Handlebars comment in proper element space', function () {
   let t = 'before <div {{! some comment }} data-foo="bar" {{! other comment }}></div> after';
   astEqual(