Regex vs. AST: Lessons from SystemVerilog Coverage Linting
Why Regex Is the Wrong Abstraction for SystemVerilog Coverage Linting When building a lint rule for SystemVerilog functional coverage, it is tempting to start with a regular expression. The problem can initially appear simple: find array-based coverpoint bins, calculate how many bins they expand into, and report a violation if the count exceeds the supported limit. A first implementation might read the source file, remove comments, and search for patterns such as bins foo[] = {[0:2048]}; . As a first-cut implementation, this is perfectly reasonable. It is small, easy to prototype, and useful for validating the basic rule logic. The problem is that regular expressions operate on source text , while a lint rule needs to reason about language structure . Consider: bins values[] = { [0:2048], [3000:4000] }; The rule now needs to understand that this is one array-bin declaration containing multiple ranges, and calculate the expansion represented by those ranges. A re...