fix: use block comments in CR mutator to prevent compilation errors

[stevennevins]

Summary

CR mutator now uses block comments (/* */) instead of line comments (//).

Problem

Line comment // comments out everything after it on the line. This breaks compilation when code continues:

// Original
function test() public onlyOwner {

// With // - BROKEN
function test() public // onlyOwner {

// With /* */ - WORKS  
function test() public /* onlyOwner */ {

Solution

new_str = "/* " + old_str + " */"

Scenarios Improved

Function modifier same line as brace:

// Original
function foo() onlyOwner {

// Before (broken)
function foo() // onlyOwner {

// After (works)
function foo() /* onlyOwner */ {

Single-line functions:

// Original
function getX() view returns (uint) { return x; }

// Before (broken) - commenting return statement
function getX() view returns (uint) { // return x; }

// After (works)
function getX() view returns (uint) { /* return x; */ }

[dguido]

Code review

Found 1 issue:

1. Byte offset used as character index - The new semicolon-checking code uses stop (a byte offset from Solidity's source mapping) as a character index into source_code (a Python string). This is incorrect for files containing multi-byte UTF-8 characters (e.g., unicode in comments or string literals). The codebase explicitly documents this limitation in source_mapping.py:content: "Use this property instead of eg source_code[start:end] Above will return incorrect content if source_code contains any unicode because self.start and self.end are byte offsets, not char offsets"

slither/slither/tools/mutator/mutators/CR.py

Lines 31 to 36 in 3fa85c3

	# Check if there's a trailing semicolon to include
	source_code = self.slither.source_code[self.in_file]
	if stop < len(source_code) and source_code[stop] == ";":
	stop += 1
	old_str += ";"

The fix should encode the source code to UTF-8 bytes before indexing, similar to how abstract_mutator.py does it:

source_bytes = self.slither.source_code[self.in_file].encode("utf8")
if stop < len(source_bytes) and source_bytes[stop:stop+1] == b";":

Reference:

slither/slither/core/source_mapping/source_mapping.py

Lines 71 to 89 in fd71cab

	def content(self) -> str:
	"""
	Return the txt content of the Source
	Use this property instead of eg source_code[start:end]
	Above will return incorrect content if source_code contains any unicode
	because self.start and self.end are byte offsets, not char offsets
	Returns: str
	"""
	# If the compilation unit was not initialized, it means that the set_offset was never called
	# on the corresponding object, which should not happen
	assert self.compilation_unit
	return (
	self.compilation_unit.core.source_code[self.filename.absolute]
	.encode("utf8")[self.start : self.end]
	.decode("utf8")
	)

🤖 Generated with Claude Code

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