Auto merge of #22086 - servo:2018-without-stylo, r=SimonSapin

Switch some crates to the 2018 edition

This is the subset of https://github.com/servo/servo/pull/22083 that doesn’t affect Gecko at all, so it isn’t blocked.

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python/servo/command_base.py

@@ -646,8 +646,6 @@ install them, let us know by filing a bug!")
             if target.startswith('arm') or target.startswith('aarch64'):
                 env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " -C target-feature=+neon"
 
-        env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " -W unused-extern-crates"
-
         git_info = []
         if os.path.isdir('.git') and is_build:
             git_sha = subprocess.check_output([

python/tidy/servo_tidy/tidy.py

@@ -256,10 +256,18 @@ def check_length(file_name, idx, line):
 
     # Prefer shorter lines when shell scripting.
     max_length = 80 if file_name.endswith(".sh") else 120
-    if len(line.rstrip('\n')) > max_length:
+    if len(line.rstrip('\n')) > max_length and not is_unsplittable(file_name, line):
         yield (idx + 1, "Line is longer than %d characters" % max_length)
 
 
+def is_unsplittable(file_name, line):
+    return (
+        file_name.endswith(".rs") and
+        line.startswith("use ") and
+        "{" not in line
+    )
+
+
 def check_whatwg_specific_url(idx, line):
     match = re.search(r"https://html\.spec\.whatwg\.org/multipage/[\w-]+\.html#([\w\:-]+)", line)
     if match is not None: