Bug 1241398 - Show the diff for created and deleted files in mach build-backend --diff. r=gps

python/mozbuild/mozbuild/backend/base.py

@@ -20,7 +20,10 @@ from mach.mixin.logging import LoggingMixin
 import mozpack.path as mozpath
 from ..preprocessor import Preprocessor
 from ..pythonutil import iter_modules_in_path
-from ..util import FileAvoidWrite
+from ..util import (
+    FileAvoidWrite,
+    simple_diff,
+)
 from ..frontend.data import ContextDerived
 from .configenvironment import ConfigEnvironment
 from mozbuild.base import ExecutionSummary
@@ -136,8 +139,17 @@ class BuildBackend(LoggingMixin):
         # Purge backend files created in previous run, but not created anymore
         delete_files = self._backend_output_list - self._backend_output_files
         for path in delete_files:
+            full_path = mozpath.join(self.environment.topobjdir, path)
             try:
-                os.unlink(mozpath.join(self.environment.topobjdir, path))
+                with open(full_path, 'r') as existing:
+                    old_content = existing.read()
+                    if old_content:
+                        self.file_diffs[full_path] = simple_diff(
+                            full_path, old_content.splitlines(), None)
+            except IOError:
+                pass
+            try:
+                os.unlink(full_path)
                 self._deleted_count += 1
             except OSError:
                 pass
@@ -199,12 +211,12 @@ class BuildBackend(LoggingMixin):
 
         self._backend_output_files.add(mozpath.relpath(fh.name, self.environment.topobjdir))
         existed, updated = fh.close()
+        if fh.diff:
+            self.file_diffs[fh.name] = fh.diff
         if not existed:
             self._created_count += 1
         elif updated:
             self._updated_count += 1
-            if fh.diff:
-                self.file_diffs[fh.name] = fh.diff
         else:
             self._unchanged_count += 1
 

python/mozbuild/mozbuild/util.py

@@ -111,6 +111,23 @@ def ensureParentDir(path):
                 raise
 
 
+def simple_diff(filename, old_lines, new_lines):
+    """Returns the diff between old_lines and new_lines, in unified diff form,
+    as a list of lines.
+
+    old_lines and new_lines are lists of non-newline terminated lines to
+    compare.
+    old_lines can be None, indicating a file creation.
+    new_lines can be None, indicating a file deletion.
+    """
+
+    old_name = '/dev/null' if old_lines is None else filename
+    new_name = '/dev/null' if new_lines is None else filename
+
+    return difflib.unified_diff(old_lines or [], new_lines or [],
+                                old_name, new_name, n=4, lineterm='')
+
+
 class FileAvoidWrite(BytesIO):
     """File-like object that buffers output and only writes if content changed.
 
@@ -177,11 +194,10 @@ class FileAvoidWrite(BytesIO):
 
         if self._capture_diff:
             try:
-                old_lines = old_content.splitlines() if old_content else []
+                old_lines = old_content.splitlines() if existed else None
                 new_lines = buf.splitlines()
 
-                self.diff = difflib.unified_diff(old_lines, new_lines,
-                    self.name, self.name, n=4, lineterm='')
+                self.diff = simple_diff(self.name, old_lines, new_lines)
             # FileAvoidWrite isn't unicode/bytes safe. So, files with non-ascii
             # content or opened and written in different modes may involve
             # implicit conversion and this will make Python unhappy. Since
@@ -189,7 +205,8 @@ class FileAvoidWrite(BytesIO):
             # This can go away once FileAvoidWrite uses io.BytesIO and
             # io.StringIO. But that will require a lot of work.
             except (UnicodeDecodeError, UnicodeEncodeError):
-                self.diff = 'Binary or non-ascii file changed: %s' % self.name
+                self.diff = ['Binary or non-ascii file changed: %s' %
+                             self.name]
 
         return existed, True