From 39b046007d0aa16844e9ab1d8c30c39520e1bcf2 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Sun, 6 Sep 2020 15:50:52 +0200
Subject: [PATCH] Refactor token emulator registration

Only determine needed emulators based on PHP version once, and
add an adaptor that allows treating forward and reverse emulation
the same.

Previously the isEmulationNeeded() check was too conservative,
as it also considered emulators that are not relevant for the
version. Though possibly that check should just be dropped
altogether.
---
 lib/PhpParser/Lexer/Emulative.php             | 56 ++++++++++++-------
 .../Lexer/TokenEmulator/ReverseEmulator.php   | 32 +++++++++++
 2 files changed, 68 insertions(+), 20 deletions(-)
 create mode 100644 lib/PhpParser/Lexer/TokenEmulator/ReverseEmulator.php

diff --git a/lib/PhpParser/Lexer/Emulative.php b/lib/PhpParser/Lexer/Emulative.php
index 4b92a67..bf4837a 100644
--- a/lib/PhpParser/Lexer/Emulative.php
+++ b/lib/PhpParser/Lexer/Emulative.php
@@ -10,6 +10,7 @@ use PhpParser\Lexer\TokenEmulator\FnTokenEmulator;
 use PhpParser\Lexer\TokenEmulator\MatchTokenEmulator;
 use PhpParser\Lexer\TokenEmulator\NullsafeTokenEmulator;
 use PhpParser\Lexer\TokenEmulator\NumericLiteralSeparatorEmulator;
+use PhpParser\Lexer\TokenEmulator\ReverseEmulator;
 use PhpParser\Lexer\TokenEmulator\TokenEmulatorInterface;
 use PhpParser\Parser\Tokens;
 
@@ -29,7 +30,7 @@ REGEX;
     private $patches = [];
 
     /** @var TokenEmulatorInterface[] */
-    private $tokenEmulators = [];
+    private $emulators = [];
 
     /** @var string */
     private $targetPhpVersion;
@@ -46,11 +47,24 @@ REGEX;
 
         parent::__construct($options);
 
-        $this->tokenEmulators[] = new FnTokenEmulator();
-        $this->tokenEmulators[] = new MatchTokenEmulator();
-        $this->tokenEmulators[] = new CoaleseEqualTokenEmulator();
-        $this->tokenEmulators[] = new NumericLiteralSeparatorEmulator();
-        $this->tokenEmulators[] = new NullsafeTokenEmulator();
+        $emulators = [
+            new FnTokenEmulator(),
+            new MatchTokenEmulator(),
+            new CoaleseEqualTokenEmulator(),
+            new NumericLiteralSeparatorEmulator(),
+            new NullsafeTokenEmulator(),
+        ];
+
+        // Collect emulators that are relevant for the PHP version we're running
+        // and the PHP version we're targeting for emulation.
+        foreach ($emulators as $emulator) {
+            $emulatorPhpVersion = $emulator->getPhpVersion();
+            if ($this->isForwardEmulationNeeded($emulatorPhpVersion)) {
+                $this->emulators[] = $emulator;
+            } else if ($this->isReverseEmulationNeeded($emulatorPhpVersion)) {
+                $this->emulators[] = new ReverseEmulator($emulator);
+            }
+        }
     }
 
     public function startLexing(string $code, ErrorHandler $errorHandler = null) {
@@ -77,24 +91,26 @@ REGEX;
             }
         }
 
-        foreach ($this->tokenEmulators as $tokenEmulator) {
-            $emulatorPhpVersion = $tokenEmulator->getPhpVersion();
-            if (version_compare(\PHP_VERSION, $emulatorPhpVersion, '<')
-                    && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '>=')
-                    && $tokenEmulator->isEmulationNeeded($code)) {
-                $this->tokens = $tokenEmulator->emulate($code, $this->tokens);
-            } else if (version_compare(\PHP_VERSION, $emulatorPhpVersion, '>=')
-                    && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '<')
-                    && $tokenEmulator->isEmulationNeeded($code)) {
-                $this->tokens = $tokenEmulator->reverseEmulate($code, $this->tokens);
+        foreach ($this->emulators as $emulator) {
+            if ($emulator->isEmulationNeeded($code)) {
+                $this->tokens = $emulator->emulate($code, $this->tokens);
             }
         }
     }
 
+    private function isForwardEmulationNeeded(string $emulatorPhpVersion): bool {
+        return version_compare(\PHP_VERSION, $emulatorPhpVersion, '<')
+            && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '>=');
+    }
+
+    private function isReverseEmulationNeeded(string $emulatorPhpVersion): bool {
+        return version_compare(\PHP_VERSION, $emulatorPhpVersion, '>=')
+            && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '<');
+    }
+
     private function isHeredocNowdocEmulationNeeded(string $code): bool
     {
-        // skip version where this works without emulation
-        if (version_compare(\PHP_VERSION, self::PHP_7_3, '>=')) {
+        if (!$this->isForwardEmulationNeeded(self::PHP_7_3)) {
             return false;
         }
 
@@ -148,8 +164,8 @@ REGEX;
 
     private function isEmulationNeeded(string $code): bool
     {
-        foreach ($this->tokenEmulators as $emulativeToken) {
-            if ($emulativeToken->isEmulationNeeded($code)) {
+        foreach ($this->emulators as $emulator) {
+            if ($emulator->isEmulationNeeded($code)) {
                 return true;
             }
         }
diff --git a/lib/PhpParser/Lexer/TokenEmulator/ReverseEmulator.php b/lib/PhpParser/Lexer/TokenEmulator/ReverseEmulator.php
new file mode 100644
index 0000000..d324f63
--- /dev/null
+++ b/lib/PhpParser/Lexer/TokenEmulator/ReverseEmulator.php
@@ -0,0 +1,32 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\Lexer\TokenEmulator;
+
+/**
+ * Reverses emulation direction of the inner emulator.
+ */
+final class ReverseEmulator implements TokenEmulatorInterface
+{
+    /** @var TokenEmulatorInterface Inner emulator */
+    private $emulator;
+
+    public function __construct(TokenEmulatorInterface $emulator) {
+        $this->emulator = $emulator;
+    }
+
+    public function getPhpVersion(): string {
+        return $this->emulator->getPhpVersion();
+    }
+
+    public function isEmulationNeeded(string $code): bool {
+        return $this->emulator->isEmulationNeeded($code);
+    }
+
+    public function emulate(string $code, array $tokens): array {
+        return $this->emulator->reverseEmulate($code, $tokens);
+    }
+
+    public function reverseEmulate(string $code, array $tokens): array {
+        return $this->emulator->emulate($code, $tokens);
+    }
+}
\ No newline at end of file