Question

How does Mercurial tell a file was modified?

The reason I am asking is because when I run hg status its telling me several files are modified.
However, when I run hg diff there are no changes to report.

I have a theory as why this is happening: (but I am not positive)

I am using NetBeans which has Mercurial support built in. When I edit a file, it shows it as modified, although if I undo (rather than revert) those changes and save it, NetBeans tells me there are no local changes. So I am guessing NetBeans uses diffs to check for modifications while Mercurial is using something else like modification-date.

Is this correct or is something else the cause?

Answer 1

Mercurial does not use modification date to determine the status. This can be verified with a simple experiment:

hg init
echo "This is a test" > test.txt
hg commit -Am "commit"
touch test.txt
hg status

The code which performs the status check is in dirstate.py. If the dirstate is unsure about a file’s status (e.g. because only the modification time differs, then it passes it up to localrepo.status for further analysis as seen here.

The hg help status text has some clues that may help:

status may appear to disagree with
diff if permissions have changed or a
merge has occurred. The standard diff
format does not report permission
changes and diff only reports changes
relative to one merge parent.

When you run hg diff, are you specifying any command-line options?