From 1b0580a9ec31d72097bde3d057abd6ca3b82559d Mon Sep 17 00:00:00 2001
From: Pete Bacon Darwin <pete@bacondarwin.com>
Date: Fri, 8 Feb 2019 22:10:19 +0000
Subject: [PATCH] refactor(compiler): remove unnecessary `!` operators from
 lexer (#28055)

When we added the strict null checks, the lexer had some `!`
operators added to prevent the compilation from failing.

This commit resolves this problem correctly and removes the
hacks.

Also the comment

```
// Note: this is always lowercase!
```

has been removed as it is no longer true.

See #24571

PR Close #28055
---
 packages/compiler/src/ml_parser/lexer.ts | 26 ++++++++++++++++--------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/packages/compiler/src/ml_parser/lexer.ts b/packages/compiler/src/ml_parser/lexer.ts
index 3df7c5e986..5f8b479232 100644
--- a/packages/compiler/src/ml_parser/lexer.ts
+++ b/packages/compiler/src/ml_parser/lexer.ts
@@ -36,11 +36,12 @@ export enum TokenType {
 }
 
 export class Token {
-  constructor(public type: TokenType, public parts: string[], public sourceSpan: ParseSourceSpan) {}
+  constructor(
+      public type: TokenType|null, public parts: string[], public sourceSpan: ParseSourceSpan) {}
 }
 
 export class TokenError extends ParseError {
-  constructor(errorMsg: string, public tokenType: TokenType, span: ParseSourceSpan) {
+  constructor(errorMsg: string, public tokenType: TokenType|null, span: ParseSourceSpan) {
     super(span, errorMsg);
   }
 }
@@ -86,16 +87,13 @@ class _Tokenizer {
   private _length: number;
   private _tokenizeIcu: boolean;
   private _interpolationConfig: InterpolationConfig;
-  // Note: this is always lowercase!
   private _peek: number = -1;
   private _nextPeek: number = -1;
   private _index: number = -1;
   private _line: number = 0;
   private _column: number = -1;
-  // TODO(issue/24571): remove '!'.
-  private _currentTokenStart !: ParseLocation;
-  // TODO(issue/24571): remove '!'.
-  private _currentTokenType !: TokenType;
+  private _currentTokenStart: ParseLocation|null = null;
+  private _currentTokenType: TokenType|null = null;
   private _expansionCaseStack: TokenType[] = [];
   private _inInterpolation: boolean = false;
 
@@ -206,11 +204,21 @@ class _Tokenizer {
   }
 
   private _endToken(parts: string[], end: ParseLocation = this._getLocation()): Token {
+    if (this._currentTokenStart === null) {
+      throw new TokenError(
+          'Programming error - attempted to end a token when there was no start to the token',
+          this._currentTokenType, this._getSpan(end, end));
+    }
+    if (this._currentTokenType === null) {
+      throw new TokenError(
+          'Programming error - attempted to end a token which has no token type', null,
+          this._getSpan(this._currentTokenStart, end));
+    }
     const token =
         new Token(this._currentTokenType, parts, new ParseSourceSpan(this._currentTokenStart, end));
     this.tokens.push(token);
-    this._currentTokenStart = null !;
-    this._currentTokenType = null !;
+    this._currentTokenStart = null;
+    this._currentTokenType = null;
     return token;
   }