fixup! feat(language-service): add support for text replacement

packages/language-service/src/completions.ts

@@ -32,11 +32,14 @@ function getClosestTextStartOffset(templateInfo: AstResult, position: number): n
   const {htmlAst, templateAst, template} = templateInfo;
   const templatePosition = position - template.span.start;
   const templatePath = findTemplateAstAt(templateInfo.templateAst, templatePosition);
+  // Closest HTML template AST node to the queried template position, like an element or attribute.
   const templateAstTail = templatePath.tail;
   if (!templateAstTail) {
     return 0;
   }
 
+  // If the closest HTML template node has a Angular template syntax AST inside it, extract it.
+  // Otherwise, get the text of the HTML template node, which is the closest starting text offset.
   const ast: AST|string = templateAstTail.visit(
       {
         visitNgContent: () => '',
@@ -53,15 +56,17 @@ function getClosestTextStartOffset(templateInfo: AstResult, position: number): n
         visitDirectiveProperty: ast => ast.value,
       },
       null);
-
   if (!(ast instanceof AST)) {
-    return ast.length;
+    return ast.length;  // offset of HTML template node text
   }
 
+  // Find the Angular template syntax AST closest to queried template position.
   const closestAst = findAstAt(ast, templatePosition - templateAstTail.sourceSpan.start.offset);
   const closestTail = closestAst.tail;
   if (!closestTail) return 0;
 
+  // Return the closest starting text offset in the template syntax AST, which is either the value
+  // of the AST or nothing at all.
   return closestTail.visit({
     visitBinary: ast => 0,
     visitChain: ast => 0,
@@ -152,6 +157,8 @@ export function getTemplateCompletions(
         null);
   }
 
+  // Define the span of the partial word the completion query was called on, which will be replaced
+  // by a selected completion.
   const offset = getClosestTextStartOffset(templateInfo, position);
   return result.map(entry => {
     return {