Use FileAvoidWrite in apidoc

Previously, sphinx-apidoc would always write files, even if the
auto-generated content was identical. This would bump the mtime and
cause the file to be re-read and generated on the next build invocation.
After this patch, the files are not written unless content has changed.

In a contrived example using `sphinx-apidoc` to regenerate documentation
for CPython's Lib/ directory, this patch reduced the number of "updated"
source files from 257 to 2. Execution time of `sphinx-build` without
parallelism decreased from ~12.5s to ~4.5s.

1 files changed, 2 insertions, 5 deletions

diff --git a/sphinx/apidoc.py b/sphinx/apidoc.py
index 10311e6f3..60ec278aa 100644
--- a/sphinx/apidoc.py
+++ b/sphinx/apidoc.py
@@ -21,7 +21,7 @@ import sys
 import optparse
 from os import path
 
-from sphinx.util.osutil import walk
+from sphinx.util.osutil import FileAvoidWrite, walk
 from sphinx import __display_version__
 
 # automodule options
@@ -61,11 +61,8 @@ def write_file(name, text, opts):
         print('File %s already exists, skipping.' % fname)
     else:
         print('Creating file %s.' % fname)
-        f = open(fname, 'w')
-        try:
+        with FileAvoidWrite(fname) as f:
             f.write(text)
-        finally:
-            f.close()
 
 
 def format_heading(level, text):