[Parser][NFC] Move `ParseInput` into the parser context (#5132)

Rather than passing both a `Ctx` and a `ParseInput` to every parsing function,
pass only a `Ctx` with a `ParseInput` inside of it. This significantly reduces
verbosity in the parser. To handle cases where parsing needs to happen at
specific locations, which used to be handled by constructing a new `ParseInput`
independent from the ctx, introduce a new RAII utility for temporarily changing
the location of the `ParseInput` inside a context.

Also add a utility for generating an error at a particular location to avoid
having to construct new `ParseInput` objects just for that purpose. This
resolves a few TODOs about correcting error locations, but since we don't test
those yet, I still consider this NFC.

1 files changed, 2 insertions, 2 deletions

diff --git a/scripts/gen-s-parser.py b/scripts/gen-s-parser.py
index 3b89820c7..35c0bdae3 100755
--- a/scripts/gen-s-parser.py
+++ b/scripts/gen-s-parser.py
@@ -721,7 +721,7 @@ def instruction_parser(new_parser=False):
     def print_leaf(expr, inst):
         if new_parser:
             expr = expr.replace("()", "(ctx)")
-            expr = expr.replace("(s", "(ctx, in")
+            expr = expr.replace("(s", "(ctx")
             printer.print_line("if (op == \"{inst}\"sv) {{".format(inst=inst))
             with printer.indent():
                 printer.print_line("auto ret = {expr};".format(expr=expr))
@@ -760,7 +760,7 @@ def instruction_parser(new_parser=False):
     printer.print_line("parse_error:")
     with printer.indent():
         if new_parser:
-            printer.print_line("return in.err(\"unrecognized instruction\");")
+            printer.print_line("return ctx.in.err(\"unrecognized instruction\");")
         else:
             printer.print_line("throw ParseException(std::string(op), s.line, s.col);")