[PATCH 1 of 2] verify: document corner cases

[Ryan McElroy]

On 3/30/17 5:01 PM, Jun Wu wrote:
> Excerpts from Ryan McElroy's message of 2017-03-30 09:55:50 +0100:
>> On 3/29/17 10:51 PM, Jun Wu wrote:
>>> # HG changeset patch
>>> # User Jun Wu <quark at fb.com>
>>> # Date 1490823901 25200
>>> #      Wed Mar 29 14:45:01 2017 -0700
>>> # Node ID 1f7890370b5437466534cbd0a313d21671dade03
>>> # Parent  e9fda3b8614a8b701bd48041afa8b709e1227f27
>>> verify: document corner cases
>>>
>>> It seems a good idea to list all kinds of "surprises" and expected behavior
>>> to make the upcoming changes easier to understand.
>>>
>>> Note: the comment added do not reflect the actual behavior of the current
>> grammar-nit: s/do/does
>>
>>> code.
>>>
>>> diff --git a/mercurial/verify.py b/mercurial/verify.py
>>> --- a/mercurial/verify.py
>>> +++ b/mercurial/verify.py
>>> @@ -381,4 +381,44 @@ class verifier(object):
>>>    
>>>                    # verify contents
>>> +                #
>>> +                # Define 4 cases to help understand corner cases:
>>> +                #
>>> +                #                       | common | rename | meta  | ext
>> Can you define these four words?
> The first table is supposed to define them precisely.

I guess it didn't for me, which is why I asked and thought "english 
descriptions" would be useful.

>
>> common = common case?
>> rename = file was just copied from somewhere else?
>> meta = ???
> "rename" is called "metadata" in filelog.py, so it means metadata without
> rename.

When would this happen? It's still not clear to me.

>
>> ext = extension that adds a flags processor?
>>> +                #  -------------------------------------------------------
>>> +                #   flags()             | 0      | 0      | 0     | not 0
>>> +                #   renamed()           | False  | True   | False | ?
>>> +                #   rawtext[0:2]=='\1\n'| False  | True   | True  | ?
>>> +                #
>>> +                # "rawtext" means the raw text stored in revlog data, which
>>> +                # could be retrieved by "revision(rev, raw=True)". "text"
>>> +                # mentioned below is "revision(rev, raw=False)".
>>> +                #
>>> +                # There are 3 different lengths stored physically:
>>> +                #  1. L1: rawsize, stored in revlog index
>>> +                #  2. L2: len(rawtext), stored in revlog data
>>> +                #  3. L3: len(text), stored in revlog data if flags=0, or
>>> +                #     possibly somewhere else if flags!=0
>>> +                #
>>> +                # L1 should be equal to L2. L3 is unrelated to L1 or L2. But
>> How about "L3 can be different than L1 and L2" -- it would be the same
>> if there are no flags, right?
> Yes. I notice the minor difference between the language. Thanks for the
> suggestion!
>
>>> +                # text may or may not affect commit hash depending on flag
>>> +                # processors (see revlog.addflagprocessor).
>>> +                #
>>> +                #              | common  | rename | meta  | ext
>>> +                # -------------------------------------------------
>>> +                #    rawsize() | L1      | L1     | L1    | L1
>>> +                #       size() | L1      | L2-LM  | L1(*) | L1 (?)
>>> +                # len(rawtext) | L2      | L2     | L2    | L2
>>> +                #    len(text) | L2      | L2     | L2    | L3
>>> +                #  len(read()) | L2      | L2-LM  | L2-LM | L3
>>> +                #
>>> +                # LM:  length of metadata, depending on rawtext
>>> +                # (*): not ideal, see comment in filelog.size
>>> +                # (?): could be "- len(meta)" if the resolved content has
>>> +                #      rename metadata
>>> +                #
>>> +                # Checks needed to be done:
>>> +                #  1. length check: L1 == L2, in all cases.
>>> +                #  2. hash check: depending on flag processor, we may need to
>>> +                #     use either "text" (external), or "rawtext" (in revlog).
>>>                    try:
>>>                        l = len(fl.read(n))
>> Overall this is pretty easy to follow and adds a lot of clarity. Just a
>> couple of questions inline.