Replace matching patterns at the specified locations

rewrite_rust_errors.py

#!/bin/python

# Replace matching patterns at the specified locations
#
# On stdin it expects locations (as reported by the rustc compiler):
#
#      --> path/to/file.rs:line:col
#
# Lines not matching this pattern are ignored:

marker = '^\s+--> (.+?):(\d+)'

# This program opens each file specified on the input.
# Lines not specified on the input are kept as-is.
# Each specified line is tested against the given regular expressions,
# and gets replaced by them as specified.
# Each entry in replacements is a tuple of (pattern, replacement).
# replacement can be a function, see python re::sub.

replacements = [
    ('bad', 'good'),
    ('spoiled (.+)', 'fresh \\1'),
]

# Only the first matching expression gets applied.
# The matching lines with replacement applied get written back to the input file.
# Non-matching lines are kept verbatim, with an optional warning:

warn_non_matching_line = True

# Files with multiple locations are supported.

import collections
import io
import re
import shutil
import sys

def main():
    locations = collections.defaultdict(set)
    markerex = re.compile(marker)

    for fl in sys.stdin:
        m = markerex.match(fl)
        if m:
            path, line = m[1], int(m[2])
            locations[path].add(line)

    for path, lines in locations.items():
        with open(path) as f:
            output = rewrite_file(f, lines)
        with open(path, 'w') as f:
            output.seek(0)
            shutil.copyfileobj(output, f)
        output.close()

def rewrite_file(f, lines):
    output = io.StringIO()

    for i,line in enumerate(f):
        if i+1 in lines:
            output.write(apply_replacements(line))
        else:
            output.write(line)
    return output

def apply_replacements(s):
    for pattern,repl in replacements:
        new,matched = re.subn(pattern, repl, s)
        if matched:
            return new
    if warn_non_matching_line:
        print(f'NOMATCH {s.rstrip()}')
    return s

main()