Add snake_case converter to AST generator

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/genast.py

@@ -1,12 +1,29 @@
 #!/usr/bin/env python3
 # pylint: disable=missing-function-docstring,missing-class-docstring,missing-module-docstring,line-too-long
 import abc
+import re
 import sys
 import time
 from pathlib import Path
 from typing import Self
 
 
+def snake_case(s: str):
+    # This insane regex comes from ChatGPT. I have no idea what the original
+    # source is, doing a verbatim search on Google and DDG doesn't yield any
+    # useful results.
+    #
+    # Here is the breakdown of how it works:
+    # (?<!^) - "negative lookbehind". this ensures that the position is not
+    #          preceded by a start character. If this was omitted, it would
+    #          put an underscore before the first capital letter in the string,
+    #          e.g. IndexAssign -> _index_assign
+    # (?=[A-Z]) - this is a lookahead, asserting that the next character is
+    #          uppercase. It does not consume the character, so doing a .sub()
+    #          on this will not replace it.
+    return re.sub(r"(?<!^)(?=[A-Z])", "_", s).lower()
+
+
 class SB:
     "String builder"
 
@@ -68,7 +85,7 @@ class GenerateStruct(Generator):
             + "{"
         )
         sb.indent()
-        sb.line(f"visitor.visit_{self.name.lower()}_{self.base.lower()}(self)")
+        sb.line(f"visitor.visit_{snake_case(self.name + self.base)}(self)")
 
         sb.dedent()
         sb.line("}")
@@ -82,7 +99,7 @@ class GenerateStruct(Generator):
         return str(sb)
 
     def generate_visitor(self) -> str:
-        return f"fn visit_{self.name.lower()}_{self.base.lower()}(&mut self, {self.base.lower()}: &{self.name}{self.base}) -> Result<(), Error>;"
+        return f"fn visit_{snake_case(self.name + self.base)}(&mut self, {snake_case(self.base)}: &{self.name}{self.base}) -> Result<(), Error>;"
 
 
 class GenerateEnum(Generator):
@@ -130,7 +147,7 @@ class GenerateEnum(Generator):
             + "{"
         )
         sb.indent()
-        sb.line(f"visitor.visit_{self.name.lower()}_{self.base.lower()}(self)")
+        sb.line(f"visitor.visit_{snake_case(self.name + self.base)}(self)")
 
         sb.dedent()
         sb.line("}")
@@ -144,7 +161,7 @@ class GenerateEnum(Generator):
         return str(sb)
 
     def generate_visitor(self) -> str:
-        return f"fn visit_{self.name.lower()}_{self.base.lower()}(&mut self, {self.base.lower()}: &{self.name}{self.base}) -> Result<(), Error>;"
+        return f"fn visit_{snake_case(self.name)}(&mut self, {snake_case(self.base)}: &{self.name}{self.base}) -> Result<(), Error>;"
 
 
 class GenerateGroup(Generator):