performance: slightly faster line wrap

Author: hukkin

pyproject.toml

@@ -145,6 +145,15 @@ commands = [
     ["python", "fuzzer/fuzz.py", "{toxworkdir}/fuzzer-corpus", { replace = "posargs", default = ["-len_control=10000"], extend = true }],
 ]
 
+[tool.tox.env."benchmark"]
+description = "benchmark mdformat against local doc files"
+commands = [
+    ["python", "-c", "print('Wrap mode: keep')"],
+    ["python", "-m", "timeit", "from mdformat._cli import run", 'run(["README.md", "docs/", "--check"])'],
+    ["python", "-c", "print('Wrap mode: 50')"],
+    ["python", "-m", "timeit", "from mdformat._cli import run", 'run(["README.md", "docs/", "--check", "--wrap", "50"])'],
+]
+
 
 [tool.coverage.run]
 source = ["mdformat"]

src/mdformat/renderer/_context.py

@@ -40,6 +40,7 @@
 # A marker used to indicate location of a character that should be preserved
 # during word wrap. Should be converted to the actual character after wrap.
 PRESERVE_CHAR = "\x00"
+RE_PRESERVE_CHAR = re.compile(re.escape(PRESERVE_CHAR))
 
 
 def make_render_children(separator: str) -> Render:
@@ -372,10 +373,8 @@ def _prepare_wrap(text: str) -> tuple[str, str]:
 
 
 def _recover_preserve_chars(text: str, replacements: str) -> str:
-    replacement_iterator = iter(replacements)
-    return "".join(
-        next(replacement_iterator) if c == PRESERVE_CHAR else c for c in text
-    )
+    iter_replacements = iter(replacements)
+    return RE_PRESERVE_CHAR.sub(lambda _: next(iter_replacements), text)
 
 
 def paragraph(node: RenderTreeNode, context: RenderContext) -> str:  # noqa: C901

tests/test_for_profiler.py

@@ -24,3 +24,5 @@ def test_for_profiler():
     docs_path = PROJECT_ROOT / "docs"
     readme_path = PROJECT_ROOT / "README.md"
     assert run([str(docs_path), str(readme_path), "--check"]) == 0
+    # Also profile --wrap=INT code
+    run([str(docs_path), str(readme_path), "--check", "--wrap", "50"])