src/tint/fuzzers/tint_regex_fuzzer/wgsl_mutator.h - dawn - Git at Google

 // Copyright 2021 The Dawn & Tint Authors
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // 1. Redistributions of source code must retain the above copyright notice, this
 //    list of conditions and the following disclaimer.
 //
 // 2. Redistributions in binary form must reproduce the above copyright notice,
 //    this list of conditions and the following disclaimer in the documentation
 //    and/or other materials provided with the distribution.
 //
 // 3. Neither the name of the copyright holder nor the names of its
 //    contributors may be used to endorse or promote products derived from
 //    this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 #ifndef SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_
 #define SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_

 #include <optional>
 #include <string>
 #include <unordered_set>
 #include <utility>
 #include <vector>

 #include "src/tint/fuzzers/random_generator.h"

 namespace tint::fuzzers::regex_fuzzer {

 /// Class encapsulating code for regex-based mutation of WGSL shaders.
 class WgslMutator {
   public:
     /// Constructor
     /// @param generator - pseudo-random generator to use in mutator
     explicit WgslMutator(RandomGenerator& generator);

     /// A function that, given WGSL-like string and a delimiter,
     /// generates another WGSL-like string by picking two random regions
     /// enclosed by the delimiter and swapping them.
     /// @param delimiter - the delimiter that will be used to find enclosed regions.
     /// @param wgsl_code - the initial string (WGSL code) that will be mutated.
     /// @return true if a swap happened or false otherwise.
     bool SwapRandomIntervals(const std::string& delimiter, std::string& wgsl_code);

     /// A function that, given a WGSL-like string and a delimiter,
     /// generates another WGSL-like string by deleting a random
     /// region enclosed by the delimiter.
     /// @param delimiter - the delimiter that will be used to find enclosed regions.
     /// @param wgsl_code - the initial string (WGSL code) that will be mutated.
     /// @return true if a deletion happened or false otherwise.
     bool DeleteRandomInterval(const std::string& delimiter, std::string& wgsl_code);

     /// A function that, given a WGSL-like string and a delimiter,
     /// generates another WGSL-like string by duplicating a random
     /// region enclosed by the delimiter.
     /// @param delimiter - the delimiter that will be used to find enclosed regions.
     /// @param wgsl_code - the initial string (WGSL code) that will be mutated.
     /// @return true if a duplication happened or false otherwise.
     bool DuplicateRandomInterval(const std::string& delimiter, std::string& wgsl_code);

     /// Replaces a randomly-chosen identifier in wgsl_code.
     /// @param wgsl_code - WGSL-like string where the replacement will occur.
     /// @return true if a replacement happened or false otherwise.
     bool ReplaceRandomIdentifier(std::string& wgsl_code);

     /// Replaces the value of a randomly-chosen integer with one of
     /// the values in the set {INT_MAX, INT_MIN, 0, -1}.
     /// @param wgsl_code - WGSL-like string where the replacement will occur.
     /// @return true if a replacement happened or false otherwise.
     bool ReplaceRandomIntLiteral(std::string& wgsl_code);

     /// Inserts a return statement in a randomly chosen function of a
     /// WGSL-like string. The return value is a randomly-chosen identifier
     /// or literal in the string.
     /// @param wgsl_code - WGSL-like string that will be mutated.
     /// @return true if the mutation was succesful or false otherwise.
     bool InsertReturnStatement(std::string& wgsl_code);

     /// Inserts a break or continue statement in a randomly chosen loop of a WGSL-like string.
     /// @param wgsl_code - WGSL-like string that will be mutated.
     /// @return true if the mutation was succesful or false otherwise.
     bool InsertBreakOrContinue(std::string& wgsl_code);

     /// A function that, given WGSL-like string, generates a new WGSL-like string by replacing one
     /// randomly-chosen operator in the original string with another operator.
     /// @param wgsl_code - the initial WGSL-like string that will be mutated.
     /// @return true if an operator replacement happened or false otherwise.
     bool ReplaceRandomOperator(std::string& wgsl_code);

     /// Given a WGSL-like string, replaces a random identifier that appears to be a function call
     /// with the name of a built-in function. This will often lead to an invalid module, as the
     /// mutation does not aim to check whether the original and replacement function have the same
     /// number or types of arguments.
     /// @param wgsl_code - the initial WGSL-like string that will be mutated.
     /// @return true if a function call replacement happened or false otherwise.
     bool ReplaceFunctionCallWithBuiltin(std::string& wgsl_code);

     /// Given a WGSL-like string, adds a swizzle operation to either (a) an identifier, (b) a vector
     /// initializer, or (c) an existing swizzle.
     /// @param wgsl_code - the initial WGSL-like string that will be mutated.
     /// @return true if a swizzle operation is added or false otherwise.
     bool AddSwizzle(std::string& wgsl_code);

   protected:
     /// Given index idx1 it delets the region of length interval_len
     /// starting at index idx1;
     /// @param idx1 - starting index of the first region.
     /// @param reg_len - terminating index of the second region.
     /// @param wgsl_code - the string where the swap will occur.
     void DeleteInterval(size_t idx1, size_t reg_len, std::string& wgsl_code);

     /// Given 2 indices, idx1, idx2, it inserts the region of length
     /// reg1_len starting at idx1 after idx2.
     /// @param idx1 - starting index of region.
     /// @param reg1_len - length of the region.
     /// @param idx2 - the position where the region will be inserted.
     /// @param wgsl_code - the string where the swap will occur.
     void DuplicateInterval(size_t idx1, size_t reg1_len, size_t idx2, std::string& wgsl_code);

     /// Finds a possible closing bracket corresponding to the opening
     /// bracket at position opening_bracket_pos.
     /// @param opening_bracket_pos - the position of the opening bracket.
     /// @param wgsl_code - the WGSL-like string where the closing bracket.
     /// @param opening_bracket_character - the opening bracket character, e.g. (, {, <, or [
     /// @param closing_bracket_character - the closing bracket character, e.g. ), }, >, or ]
     /// @return the position of the closing bracket or 0 if there is no closing
     /// bracket.
     size_t FindClosingBracket(size_t opening_bracket_pos,
                               const std::string& wgsl_code,
                               char opening_bracket_character,
                               char closing_bracket_character);

     /// Returns the starting position of the bodies of the functions identified by an appropriate
     /// function, together with a boolean indicating whether the function returns a value or not.
     /// @param wgsl_code - the WGSL-like string where the functions will be
     /// searched.
     /// @return a vector of pairs, where each pair provides the starting position of the function
     /// body, and the value true if and only if the function returns a value.
     std::vector<std::pair<size_t, bool>> GetFunctionBodyPositions(const std::string& wgsl_code);

     /// Returns the starting position of the bodies of the loops identified by an appropriate
     /// regular expressions.
     /// @param wgsl_code - the WGSL-like string in which loops will be searched for.
     /// @return a vector with the starting position of the loop bodies in wgsl_code.
     std::vector<size_t> GetLoopBodyPositions(const std::string& wgsl_code);

     /// A function that finds all the identifiers in a WGSL-like string.
     /// @param wgsl_code - the WGSL-like string where the identifiers will be found.
     /// @return a vector with the positions and the length of all the
     /// identifiers in wgsl_code.
     std::vector<std::pair<size_t, size_t>> GetIdentifiers(const std::string& wgsl_code);

     /// A function that finds the identifiers in a WGSL-like string that appear to be used as
     /// function names in function call expressions.
     /// @param wgsl_code - the WGSL-like string where the identifiers will be found.
     /// @return a vector with the positions and the length of all the
     /// identifiers in wgsl_code.
     std::vector<std::pair<size_t, size_t>> GetFunctionCallIdentifiers(const std::string& wgsl_code);

     /// A function that returns returns the starting position
     /// and the length of all the integer literals in a WGSL-like string.
     /// @param wgsl_code - the WGSL-like string where the int literals
     /// will be found.
     /// @return a vector with the starting positions and the length
     /// of all the integer literals.
     std::vector<std::pair<size_t, size_t>> GetIntLiterals(const std::string& wgsl_code);

     /// Replaces a region of a WGSL-like string of length id2_len starting
     /// at position idx2 with a region of length id1_len starting at
     /// position idx1.
     /// @param idx1 - starting position of the first region.
     /// @param id1_len - length of the first region.
     /// @param idx2 - starting position of the second region.
     /// @param id2_len - length of the second region.
     /// @param wgsl_code - the string where the replacement will occur.
     void ReplaceRegion(size_t idx1,
                        size_t id1_len,
                        size_t idx2,
                        size_t id2_len,
                        std::string& wgsl_code);

     /// Given 4 indices, idx1, idx2, idx3 and idx4 it swaps the regions
     /// in the interval (idx1, idx2] with the region in the interval (idx3, idx4]
     /// in wgsl_text.
     /// @param idx1 - starting index of the first region.
     /// @param reg1_len - length of the first region.
     /// @param idx2 - starting index of the second region.
     /// @param reg2_len - length of the second region.
     /// @param wgsl_code - the string where the swap will occur.
     void SwapIntervals(size_t idx1,
                        size_t reg1_len,
                        size_t idx2,
                        size_t reg2_len,
                        std::string& wgsl_code);

     /// Finds the next occurrence of an operator in a WGSL-like string from a given starting
     /// position, wrapping around to the start of the string if no operator is found before reaching
     /// the end, and returning empty of no operator is found at all. There is no guarantee that the
     /// result will correspond to a WGSL operator token, e.g. the identified characters could be
     /// part of a comment, or e.g. the file might contain >>=, in which case the operator
     /// >= will be identified should it happen that the starting index corresponds to the second >
     /// character of this operator. Given that the regex mutator does not aim to guarantee
     /// well-formed programs, these issues are acceptable.
     /// @param wgsl_code - the WGSL-like string in which operator occurrences will be found.
     /// @param start_index - the index at which search should start
     /// @return empty if no operator is found, otherwise a pair comprising the index at which the
     /// operator starts and the character length of the operator.
     std::optional<std::pair<uint32_t, uint32_t>> FindOperatorOccurrence(
         const std::string& wgsl_code,
         uint32_t start_index);

     /// Finds all the swizzle operations in a WGSL-like string.
     /// @param wgsl_code - the WGSL-like string where the swizzles will be found.
     /// @return a vector with the positions and lengths of all the swizzles in wgsl_code.
     std::vector<std::pair<size_t, size_t>> GetSwizzles(const std::string& wgsl_code);

     /// Finds all the vector initializers in a WGSL-like string.
     /// @param wgsl_code - the WGSL-like string where the vector initializers will be found.
     /// @return a vector with the positions and lengths of all the vector initializers in wgsl_code.
     std::vector<std::pair<size_t, size_t>> GetVectorInitializers(const std::string& wgsl_code);

   private:
     /// A function that given a delimiter, returns a vector that contains
     /// all the positions of the delimiter in the WGSL code.
     /// @param delimiter - the delimiter of the enclosed region.
     /// @param wgsl_code - the initial string (WGSL code) that will be mutated.
     /// @return a vector with the positions of the delimiter in the WGSL code.
     std::vector<size_t> FindDelimiterIndices(const std::string& delimiter,
                                              const std::string& wgsl_code);

     /// Replaces an interval of length `length` starting at start_index
     /// with the `replacement_text`.
     /// @param start_index - starting position of the interval to be replaced.
     /// @param length - length of the interval to be replaced.
     /// @param replacement_text - the interval that will be used as a replacement.
     /// @param wgsl_code - the WGSL-like string where the replacement will occur.
     void ReplaceInterval(size_t start_index,
                          size_t length,
                          std::string replacement_text,
                          std::string& wgsl_code);

     /// Given a string representing a WGSL operator, randomly returns a different WGSL operator in
     /// the same category as the original, where the three categories are assignment operators (such
     /// as = and +=), expression operators (such as + and ^) and increment operators (++ and --).
     /// @param existing_operator - the characters comprising some WGSL operator
     /// @return another WGSL operator falling into the same category.
     std::string ChooseRandomReplacementForOperator(const std::string& existing_operator);

     /// Yields a fixed set of commonly-used WGSL keywords. The regex fuzzer relies heavily on
     /// recognizing possible identifiers via regular expressions. There is a high chance that
     /// keywords will be recognized as identifiers, which will leads to invalid code. It is valuable
     /// for this to occur to some extent (to stress test validation), but it is useful to be able to
     /// exclude the most common keywords so that invalidity does not occur too often.
     /// @return a set of commonly-used WGSL keywords.
     static std::unordered_set<std::string> GetCommonKeywords();

     RandomGenerator& generator_;
 };

 }  // namespace tint::fuzzers::regex_fuzzer

 #endif  // SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_
	// Copyright 2021 The Dawn & Tint Authors
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// 1. Redistributions of source code must retain the above copyright notice, this
	// list of conditions and the following disclaimer.
	//
	// 2. Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	//
	// 3. Neither the name of the copyright holder nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
	// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	#ifndef SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_
	#define SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_

	#include <optional>
	#include <string>
	#include <unordered_set>
	#include <utility>
	#include <vector>

	#include "src/tint/fuzzers/random_generator.h"

	namespace tint::fuzzers::regex_fuzzer {

	/// Class encapsulating code for regex-based mutation of WGSL shaders.
	class WgslMutator {
	public:
	/// Constructor
	/// @param generator - pseudo-random generator to use in mutator
	explicit WgslMutator(RandomGenerator& generator);

	/// A function that, given WGSL-like string and a delimiter,
	/// generates another WGSL-like string by picking two random regions
	/// enclosed by the delimiter and swapping them.
	/// @param delimiter - the delimiter that will be used to find enclosed regions.
	/// @param wgsl_code - the initial string (WGSL code) that will be mutated.
	/// @return true if a swap happened or false otherwise.
	bool SwapRandomIntervals(const std::string& delimiter, std::string& wgsl_code);

	/// A function that, given a WGSL-like string and a delimiter,
	/// generates another WGSL-like string by deleting a random
	/// region enclosed by the delimiter.
	/// @param delimiter - the delimiter that will be used to find enclosed regions.
	/// @param wgsl_code - the initial string (WGSL code) that will be mutated.
	/// @return true if a deletion happened or false otherwise.
	bool DeleteRandomInterval(const std::string& delimiter, std::string& wgsl_code);

	/// A function that, given a WGSL-like string and a delimiter,
	/// generates another WGSL-like string by duplicating a random
	/// region enclosed by the delimiter.
	/// @param delimiter - the delimiter that will be used to find enclosed regions.
	/// @param wgsl_code - the initial string (WGSL code) that will be mutated.
	/// @return true if a duplication happened or false otherwise.
	bool DuplicateRandomInterval(const std::string& delimiter, std::string& wgsl_code);

	/// Replaces a randomly-chosen identifier in wgsl_code.
	/// @param wgsl_code - WGSL-like string where the replacement will occur.
	/// @return true if a replacement happened or false otherwise.
	bool ReplaceRandomIdentifier(std::string& wgsl_code);

	/// Replaces the value of a randomly-chosen integer with one of
	/// the values in the set {INT_MAX, INT_MIN, 0, -1}.
	/// @param wgsl_code - WGSL-like string where the replacement will occur.
	/// @return true if a replacement happened or false otherwise.
	bool ReplaceRandomIntLiteral(std::string& wgsl_code);

	/// Inserts a return statement in a randomly chosen function of a
	/// WGSL-like string. The return value is a randomly-chosen identifier
	/// or literal in the string.
	/// @param wgsl_code - WGSL-like string that will be mutated.
	/// @return true if the mutation was succesful or false otherwise.
	bool InsertReturnStatement(std::string& wgsl_code);

	/// Inserts a break or continue statement in a randomly chosen loop of a WGSL-like string.
	/// @param wgsl_code - WGSL-like string that will be mutated.
	/// @return true if the mutation was succesful or false otherwise.
	bool InsertBreakOrContinue(std::string& wgsl_code);

	/// A function that, given WGSL-like string, generates a new WGSL-like string by replacing one
	/// randomly-chosen operator in the original string with another operator.
	/// @param wgsl_code - the initial WGSL-like string that will be mutated.
	/// @return true if an operator replacement happened or false otherwise.
	bool ReplaceRandomOperator(std::string& wgsl_code);

	/// Given a WGSL-like string, replaces a random identifier that appears to be a function call
	/// with the name of a built-in function. This will often lead to an invalid module, as the
	/// mutation does not aim to check whether the original and replacement function have the same
	/// number or types of arguments.
	/// @param wgsl_code - the initial WGSL-like string that will be mutated.
	/// @return true if a function call replacement happened or false otherwise.
	bool ReplaceFunctionCallWithBuiltin(std::string& wgsl_code);

	/// Given a WGSL-like string, adds a swizzle operation to either (a) an identifier, (b) a vector
	/// initializer, or (c) an existing swizzle.
	/// @param wgsl_code - the initial WGSL-like string that will be mutated.
	/// @return true if a swizzle operation is added or false otherwise.
	bool AddSwizzle(std::string& wgsl_code);

	protected:
	/// Given index idx1 it delets the region of length interval_len
	/// starting at index idx1;
	/// @param idx1 - starting index of the first region.
	/// @param reg_len - terminating index of the second region.
	/// @param wgsl_code - the string where the swap will occur.
	void DeleteInterval(size_t idx1, size_t reg_len, std::string& wgsl_code);

	/// Given 2 indices, idx1, idx2, it inserts the region of length
	/// reg1_len starting at idx1 after idx2.
	/// @param idx1 - starting index of region.
	/// @param reg1_len - length of the region.
	/// @param idx2 - the position where the region will be inserted.
	/// @param wgsl_code - the string where the swap will occur.
	void DuplicateInterval(size_t idx1, size_t reg1_len, size_t idx2, std::string& wgsl_code);

	/// Finds a possible closing bracket corresponding to the opening
	/// bracket at position opening_bracket_pos.
	/// @param opening_bracket_pos - the position of the opening bracket.
	/// @param wgsl_code - the WGSL-like string where the closing bracket.
	/// @param opening_bracket_character - the opening bracket character, e.g. (, {, <, or [
	/// @param closing_bracket_character - the closing bracket character, e.g. ), }, >, or ]
	/// @return the position of the closing bracket or 0 if there is no closing
	/// bracket.
	size_t FindClosingBracket(size_t opening_bracket_pos,
	const std::string& wgsl_code,
	char opening_bracket_character,
	char closing_bracket_character);

	/// Returns the starting position of the bodies of the functions identified by an appropriate
	/// function, together with a boolean indicating whether the function returns a value or not.
	/// @param wgsl_code - the WGSL-like string where the functions will be
	/// searched.
	/// @return a vector of pairs, where each pair provides the starting position of the function
	/// body, and the value true if and only if the function returns a value.
	std::vector<std::pair<size_t, bool>> GetFunctionBodyPositions(const std::string& wgsl_code);

	/// Returns the starting position of the bodies of the loops identified by an appropriate
	/// regular expressions.
	/// @param wgsl_code - the WGSL-like string in which loops will be searched for.
	/// @return a vector with the starting position of the loop bodies in wgsl_code.
	std::vector<size_t> GetLoopBodyPositions(const std::string& wgsl_code);

	/// A function that finds all the identifiers in a WGSL-like string.
	/// @param wgsl_code - the WGSL-like string where the identifiers will be found.
	/// @return a vector with the positions and the length of all the
	/// identifiers in wgsl_code.
	std::vector<std::pair<size_t, size_t>> GetIdentifiers(const std::string& wgsl_code);

	/// A function that finds the identifiers in a WGSL-like string that appear to be used as
	/// function names in function call expressions.
	/// @param wgsl_code - the WGSL-like string where the identifiers will be found.
	/// @return a vector with the positions and the length of all the
	/// identifiers in wgsl_code.
	std::vector<std::pair<size_t, size_t>> GetFunctionCallIdentifiers(const std::string& wgsl_code);

	/// A function that returns returns the starting position
	/// and the length of all the integer literals in a WGSL-like string.
	/// @param wgsl_code - the WGSL-like string where the int literals
	/// will be found.
	/// @return a vector with the starting positions and the length
	/// of all the integer literals.
	std::vector<std::pair<size_t, size_t>> GetIntLiterals(const std::string& wgsl_code);

	/// Replaces a region of a WGSL-like string of length id2_len starting
	/// at position idx2 with a region of length id1_len starting at
	/// position idx1.
	/// @param idx1 - starting position of the first region.
	/// @param id1_len - length of the first region.
	/// @param idx2 - starting position of the second region.
	/// @param id2_len - length of the second region.
	/// @param wgsl_code - the string where the replacement will occur.
	void ReplaceRegion(size_t idx1,
	size_t id1_len,
	size_t idx2,
	size_t id2_len,
	std::string& wgsl_code);

	/// Given 4 indices, idx1, idx2, idx3 and idx4 it swaps the regions
	/// in the interval (idx1, idx2] with the region in the interval (idx3, idx4]
	/// in wgsl_text.
	/// @param idx1 - starting index of the first region.
	/// @param reg1_len - length of the first region.
	/// @param idx2 - starting index of the second region.
	/// @param reg2_len - length of the second region.
	/// @param wgsl_code - the string where the swap will occur.
	void SwapIntervals(size_t idx1,
	size_t reg1_len,
	size_t idx2,
	size_t reg2_len,
	std::string& wgsl_code);

	/// Finds the next occurrence of an operator in a WGSL-like string from a given starting
	/// position, wrapping around to the start of the string if no operator is found before reaching
	/// the end, and returning empty of no operator is found at all. There is no guarantee that the
	/// result will correspond to a WGSL operator token, e.g. the identified characters could be
	/// part of a comment, or e.g. the file might contain >>=, in which case the operator
	/// >= will be identified should it happen that the starting index corresponds to the second >
	/// character of this operator. Given that the regex mutator does not aim to guarantee
	/// well-formed programs, these issues are acceptable.
	/// @param wgsl_code - the WGSL-like string in which operator occurrences will be found.
	/// @param start_index - the index at which search should start
	/// @return empty if no operator is found, otherwise a pair comprising the index at which the
	/// operator starts and the character length of the operator.
	std::optional<std::pair<uint32_t, uint32_t>> FindOperatorOccurrence(
	const std::string& wgsl_code,
	uint32_t start_index);

	/// Finds all the swizzle operations in a WGSL-like string.
	/// @param wgsl_code - the WGSL-like string where the swizzles will be found.
	/// @return a vector with the positions and lengths of all the swizzles in wgsl_code.
	std::vector<std::pair<size_t, size_t>> GetSwizzles(const std::string& wgsl_code);

	/// Finds all the vector initializers in a WGSL-like string.
	/// @param wgsl_code - the WGSL-like string where the vector initializers will be found.
	/// @return a vector with the positions and lengths of all the vector initializers in wgsl_code.
	std::vector<std::pair<size_t, size_t>> GetVectorInitializers(const std::string& wgsl_code);

	private:
	/// A function that given a delimiter, returns a vector that contains
	/// all the positions of the delimiter in the WGSL code.
	/// @param delimiter - the delimiter of the enclosed region.
	/// @param wgsl_code - the initial string (WGSL code) that will be mutated.
	/// @return a vector with the positions of the delimiter in the WGSL code.
	std::vector<size_t> FindDelimiterIndices(const std::string& delimiter,
	const std::string& wgsl_code);

	/// Replaces an interval of length `length` starting at start_index
	/// with the `replacement_text`.
	/// @param start_index - starting position of the interval to be replaced.
	/// @param length - length of the interval to be replaced.
	/// @param replacement_text - the interval that will be used as a replacement.
	/// @param wgsl_code - the WGSL-like string where the replacement will occur.
	void ReplaceInterval(size_t start_index,
	size_t length,
	std::string replacement_text,
	std::string& wgsl_code);

	/// Given a string representing a WGSL operator, randomly returns a different WGSL operator in
	/// the same category as the original, where the three categories are assignment operators (such
	/// as = and +=), expression operators (such as + and ^) and increment operators (++ and --).
	/// @param existing_operator - the characters comprising some WGSL operator
	/// @return another WGSL operator falling into the same category.
	std::string ChooseRandomReplacementForOperator(const std::string& existing_operator);

	/// Yields a fixed set of commonly-used WGSL keywords. The regex fuzzer relies heavily on
	/// recognizing possible identifiers via regular expressions. There is a high chance that
	/// keywords will be recognized as identifiers, which will leads to invalid code. It is valuable
	/// for this to occur to some extent (to stress test validation), but it is useful to be able to
	/// exclude the most common keywords so that invalidity does not occur too often.
	/// @return a set of commonly-used WGSL keywords.
	static std::unordered_set<std::string> GetCommonKeywords();

	RandomGenerator& generator_;
	};

	} // namespace tint::fuzzers::regex_fuzzer

	#endif // SRC_TINT_FUZZERS_TINT_REGEX_FUZZER_WGSL_MUTATOR_H_