From 1daa5158ebb37f1b7f8fb8210559be0c4ff30164 Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Wed, 28 Oct 2020 09:29:03 +0000
Subject: [PATCH] AK: Add GenericLexer::retreat()

This allows going back one character at a time, and then re-consume
previously consumed chars.
The code I need this for looks something like this:

    ASSERT(lexer.consume_specific('\\'));
    if (lexer.next_is("foo"))
        ...
    lexer.retreat();
    lexer.consume_escaped_character();  // This expects lexer.peek() == '\\'
---
 AK/GenericLexer.cpp | 7 +++++++
 AK/GenericLexer.h   | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/AK/GenericLexer.cpp b/AK/GenericLexer.cpp
index 565ecf3917..4ea809973f 100644
--- a/AK/GenericLexer.cpp
+++ b/AK/GenericLexer.cpp
@@ -76,6 +76,13 @@ bool GenericLexer::next_is(const char* expected) const
     return true;
 }
 
+// Go back to the previous character
+void GenericLexer::retreat()
+{
+    ASSERT(m_index > 0);
+    m_index--;
+}
+
 // Consume a character and advance the parser index
 char GenericLexer::consume()
 {
diff --git a/AK/GenericLexer.h b/AK/GenericLexer.h
index ce5d123f16..854bc96a21 100644
--- a/AK/GenericLexer.h
+++ b/AK/GenericLexer.h
@@ -48,6 +48,8 @@ public:
     bool next_is(StringView) const;
     bool next_is(const char*) const;
 
+    void retreat();
+
     char consume();
     bool consume_specific(char);
     bool consume_specific(StringView);