Add pcre2 as re2 fallback

.gitmodules

@@ -10,3 +10,6 @@
 [submodule "third-party/json"]
 	path = third-party/json
 	url = https://github.com/nlohmann/json.git
+[submodule "third-party/pcre2"]
+	path = third-party/pcre2
+	url = https://github.com/PCRE2Project/pcre2.git

CMakeLists.txt

@@ -29,6 +29,19 @@ set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third-party/abseil-cpp)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third-party/re2)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third-party/sentencepiece)
+
+# Configure PCRE2
+set(PCRE2_BUILD_PCRE2_8 ON)
+set(PCRE2_BUILD_PCRE2_16 OFF)
+set(PCRE2_BUILD_PCRE2_32 OFF)
+set(PCRE2_BUILD_TESTS OFF)
+set(PCRE2_BUILD_PCRE2GREP OFF)
+set(PCRE2_BUILD_PCRE2TEST OFF)
+set(PCRE2_BUILD_PCRE2GPERF OFF)
+set(PCRE2_BUILD_DOCS OFF)
+set(PCRE2_BUILD_LIBPCRE2_PDB OFF)
+add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third-party/pcre2)
+
 set(CMAKE_POSITION_INDEPENDENT_CODE ${_pic_flag})
 
 file(GLOB tokenizers_source_files ${CMAKE_CURRENT_SOURCE_DIR}/src/*.cpp)
@@ -45,9 +58,10 @@ target_include_directories(
          ${CMAKE_CURRENT_SOURCE_DIR}/third-party/sentencepiece/src
          ${CMAKE_CURRENT_SOURCE_DIR}/third-party/re2
          ${CMAKE_CURRENT_SOURCE_DIR}/third-party/json/single_include
-         ${CMAKE_CURRENT_SOURCE_DIR}/third-party/llama.cpp-unicode/include)
+         ${CMAKE_CURRENT_SOURCE_DIR}/third-party/llama.cpp-unicode/include
+         ${CMAKE_CURRENT_SOURCE_DIR}/third-party/pcre2/src)
 
-target_link_libraries(tokenizers PUBLIC sentencepiece-static re2::re2)
+target_link_libraries(tokenizers PUBLIC sentencepiece-static re2::re2 pcre2-8)
 
 # Build test
 if(TOKENIZERS_BUILD_TEST)
@@ -77,7 +91,8 @@ if(TOKENIZERS_BUILD_TEST)
               ${CMAKE_CURRENT_SOURCE_DIR}/include
               ${CMAKE_CURRENT_SOURCE_DIR}/third-party/sentencepiece
               ${CMAKE_CURRENT_SOURCE_DIR}/third-party/re2
-              ${CMAKE_CURRENT_SOURCE_DIR}/third-party/json/single_include)
+              ${CMAKE_CURRENT_SOURCE_DIR}/third-party/json/single_include
+              ${CMAKE_CURRENT_SOURCE_DIR}/third-party/pcre2/src)
     target_link_libraries(${test_name} gtest_main GTest::gmock tokenizers)
     add_test(${test_name} "${test_name}")
     set_tests_properties(${test_name} PROPERTIES ENVIRONMENT ${test_env})

include/pytorch/tokenizers/pcre2_regex.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <memory>
+#include <string>
+
+// Define PCRE2 code unit width before including pcre2.h
+#define PCRE2_CODE_UNIT_WIDTH 8
+#include <pcre2.h>
+
+#include <pytorch/tokenizers/regex.h>
+
+namespace tokenizers {
+
+/**
+ * @brief PCRE2-based implementation of IRegex.
+ */
+class Pcre2Regex : public IRegex {
+ public:
+  /**
+   * @brief Construct a PCRE2 regex with the given pattern.
+   *
+   * @param pattern The regex pattern to compile.
+   */
+  explicit Pcre2Regex(const std::string& pattern);
+
+  /**
+   * @brief Destructor to clean up PCRE2 resources.
+   */
+  ~Pcre2Regex();
+
+  /**
+   * @brief Return all non-overlapping matches found in the input string.
+   */
+  virtual std::vector<Match> find_all(const std::string& text) const override;
+
+ private:
+  pcre2_code* regex_;
+  pcre2_match_data* match_data_;
+
+  friend Result<std::unique_ptr<IRegex>> create_regex(
+      const std::string& pattern);
+};
+
+} // namespace tokenizers

src/pcre2_regex.cpp

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <iostream>
+#include <vector>
+
+#include <pytorch/tokenizers/pcre2_regex.h>
+
+namespace tokenizers {
+
+Pcre2Regex::Pcre2Regex(const std::string& pattern)
+    : regex_(nullptr), match_data_(nullptr) {
+  int error_code;
+  PCRE2_SIZE error_offset;
+
+  // Compile the pattern
+  regex_ = pcre2_compile(
+      reinterpret_cast<PCRE2_SPTR>(pattern.c_str()),
+      pattern.length(),
+      PCRE2_UCP | PCRE2_UTF, // Enable Unicode support and UTF-8 mode
+      &error_code,
+      &error_offset,
+      nullptr);
+
+  if (regex_ == nullptr) {
+    PCRE2_UCHAR error_buffer[256];
+    pcre2_get_error_message(error_code, error_buffer, sizeof(error_buffer));
+    std::cerr << "PCRE2 compilation failed at offset " << error_offset << ": "
+              << error_buffer << std::endl;
+    return;
+  }
+
+  // Create match data
+  match_data_ = pcre2_match_data_create_from_pattern(regex_, nullptr);
+  if (match_data_ == nullptr) {
+    pcre2_code_free(regex_);
+    regex_ = nullptr;
+    std::cerr << "Failed to create PCRE2 match data" << std::endl;
+    return;
+  }
+}
+
+Pcre2Regex::~Pcre2Regex() {
+  if (match_data_) {
+    pcre2_match_data_free(match_data_);
+  }
+  if (regex_) {
+    pcre2_code_free(regex_);
+  }
+}
+
+std::vector<Match> Pcre2Regex::find_all(const std::string& text) const {
+  std::vector<Match> result;
+
+  if (!regex_ || !match_data_) {
+    return result;
+  }
+
+  PCRE2_SIZE* ovector;
+  PCRE2_SPTR subject = reinterpret_cast<PCRE2_SPTR>(text.c_str());
+  PCRE2_SIZE subject_length = text.length();
+  PCRE2_SIZE offset = 0;
+
+  while (offset < subject_length) {
+    int rc = pcre2_match(
+        regex_,
+        subject,
+        subject_length,
+        offset,
+        0, // Default options
+        match_data_,
+        nullptr);
+
+    if (rc < 0) {
+      if (rc == PCRE2_ERROR_NOMATCH) {
+        break; // No more matches
+      } else {
+        // Error occurred
+        PCRE2_UCHAR error_buffer[256];
+        pcre2_get_error_message(rc, error_buffer, sizeof(error_buffer));
+        std::cerr << "PCRE2 matching error: " << error_buffer << std::endl;
+        break;
+      }
+    }
+
+    ovector = pcre2_get_ovector_pointer(match_data_);
+
+    // Add the match to the result
+    result.push_back({ovector[0], ovector[1]});
+
+    // Move to the next position after the match
+    offset = ovector[1];
+
+    // If the match was empty, move forward by one character to avoid infinite
+    // loop
+    if (ovector[0] == ovector[1]) {
+      offset++;
+    }
+  }
+
+  return result;
+}
+
+} // namespace tokenizers

src/regex.cpp

@@ -6,6 +6,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <pytorch/tokenizers/pcre2_regex.h>
 #include <pytorch/tokenizers/re2_regex.h>
 #include <pytorch/tokenizers/regex.h>
 #include <pytorch/tokenizers/std_regex.h>
@@ -18,8 +19,8 @@ namespace tokenizers {
 
 /**
  * @brief Factory function that creates a regex object using RE2 if possible.
- *        Falls back to std::regex if RE2 rejects the pattern with
- *        ErrorBadPerlOp.
+ *        Falls back to PCRE2 if RE2 rejects the pattern, then to std::regex if
+ * PCRE2 fails.
  */
 Result<std::unique_ptr<IRegex>> create_regex(const std::string& pattern) {
   // Try RE2 first
@@ -30,10 +31,20 @@ Result<std::unique_ptr<IRegex>> create_regex(const std::string& pattern) {
   }
 
   if (re2->regex_->error_code() == re2::RE2::ErrorBadPerlOp) {
-    try {
+    // RE2 doesn't support some Perl features, try PCRE2
+    auto pcre2 = std::make_unique<Pcre2Regex>("(" + pattern + ")");
+
+    if (pcre2->regex_ != nullptr && pcre2->match_data_ != nullptr) {
       std::cout
           << "RE2 is unable to support things such as negative lookaheads in "
-          << pattern << ", defaulting to std::regex.";
+          << pattern << ", using PCRE2 instead." << std::endl;
+      return static_cast<std::unique_ptr<IRegex>>(std::move(pcre2));
+    }
+
+    // If PCRE2 also fails, fall back to std::regex
+    try {
+      std::cout
+          << "PCRE2 failed to compile pattern, falling back to std::regex.";
       auto std_regex = std::make_unique<StdRegex>("(" + pattern + ")");
       return static_cast<std::unique_ptr<IRegex>>(std::move(std_regex));
     } catch (const std::regex_error& e) {

targets.bzl

@@ -28,6 +28,9 @@ def define_common_targets():
         srcs = ["src/regex.cpp"] + glob([
             "src/*_regex.cpp",
         ]),
+        deps = [
+            "fbsource//third-party/pcre2:pcre2-8",
+        ],
         exported_headers = subdir_glob([
             ("include", "pytorch/tokenizers/regex.h"),
             ("include", "pytorch/tokenizers/*_regex.h"),

test/test_regex.cpp

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+
+#include "pytorch/tokenizers/pcre2_regex.h"
+#include "pytorch/tokenizers/re2_regex.h"
+#include "pytorch/tokenizers/regex.h"
+
+using namespace tokenizers;
+
+class RegexTest : public ::testing::Test {};
+
+// Test basic functionality
+TEST_F(RegexTest, BasicMatching) {
+  auto regex = TK_UNWRAP_THROW(create_regex("\\w+"));
+
+  std::string text = "Hello world";
+  auto matches = regex->find_all(text);
+  ASSERT_EQ(matches.size(), 2);
+  EXPECT_EQ(matches[0].start, 0);
+  EXPECT_EQ(matches[0].end, 5);
+  EXPECT_EQ(
+      text.substr(matches[0].start, matches[0].end - matches[0].start),
+      "Hello");
+  EXPECT_EQ(matches[1].start, 6);
+  EXPECT_EQ(matches[1].end, 11);
+  EXPECT_EQ(
+      text.substr(matches[1].start, matches[1].end - matches[1].start),
+      "world");
+}
+
+// Test pattern that only PCRE2 supports (lookbehind)
+TEST_F(RegexTest, Pcre2Specific) {
+  const std::string pattern = "(?<=@)\\w+";
+
+  // Verify that the factory function fallsback on a PCRE2 regex
+  auto regex = TK_UNWRAP_THROW(create_regex(pattern));
+  EXPECT_NE(dynamic_cast<Pcre2Regex*>(regex.get()), nullptr);
+
+  std::string text = "[email protected]";
+  auto matches = regex->find_all(text);
+  ASSERT_EQ(matches.size(), 1);
+  EXPECT_EQ(matches[0].start, 5);
+  EXPECT_EQ(matches[0].end, 12);
+  EXPECT_EQ(
+      text.substr(matches[0].start, matches[0].end - matches[0].start),
+      "example");
+}
+
+// Test complex pattern with negative lookahead that should fall back to PCRE2.
+// This specific pattern is from the Qwen2.5 1.5B pretokenizer.
+// https://huggingface.co/Qwen/Qwen2.5-1.5B/raw/main/tokenizer.json
+TEST_F(RegexTest, ComplexPatternWithNegativeLookahead) {
+  const std::string complex_pattern =
+      "(?i:'s|'t|'re|'ve|'m|'ll|'d)|[^\\r\\n\\p{L}\\p{N}]?\\p{L}+|\\p{N}| ?[^\\s\\p{L}\\p{N}]+[\\r\\n]*|\\s*[\\r\\n]+|\\s+(?!\\S)|\\s+";
+
+  // Now verify that the factory function fallsback on a PCRE2 regex
+  auto regex = TK_UNWRAP_THROW(create_regex(complex_pattern));
+  EXPECT_NE(dynamic_cast<Pcre2Regex*>(regex.get()), nullptr);
+
+  // Test the pattern with some sample text
+  std::string text = "Hello's world\n  test";
+  auto matches = regex->find_all(text);
+
+  // We expect to match:
+  // 1. "Hello" (word)
+  // 2. "'s" (contraction)
+  // 3. " world" (word with leading space)
+  // 4. "\n" (newline)
+  // 5. " " (whitespace)
+  // 6. " test" (word with leading space)
+  ASSERT_EQ(matches.size(), 6);
+
+  EXPECT_EQ(matches[0].start, 0);
+  EXPECT_EQ(matches[0].end, 5);
+  EXPECT_EQ(
+      text.substr(matches[0].start, matches[0].end - matches[0].start),
+      "Hello");
+  EXPECT_EQ(matches[1].start, 5);
+  EXPECT_EQ(matches[1].end, 7);
+  EXPECT_EQ(
+      text.substr(matches[1].start, matches[1].end - matches[1].start), "'s");
+  EXPECT_EQ(matches[2].start, 7);
+  EXPECT_EQ(matches[2].end, 13);
+  EXPECT_EQ(
+      text.substr(matches[2].start, matches[2].end - matches[2].start),
+      " world");
+  EXPECT_EQ(matches[3].start, 13);
+  EXPECT_EQ(matches[3].end, 14);
+  EXPECT_EQ(
+      text.substr(matches[3].start, matches[3].end - matches[3].start), "\n");
+  EXPECT_EQ(matches[4].start, 14);
+  EXPECT_EQ(matches[4].end, 15);
+  EXPECT_EQ(
+      text.substr(matches[4].start, matches[4].end - matches[4].start), " ");
+  EXPECT_EQ(matches[5].start, 15);
+  EXPECT_EQ(matches[5].end, 20);
+  EXPECT_EQ(
+      text.substr(matches[5].start, matches[5].end - matches[5].start),
+      " test");
+}