[PATCH 1 of 2 V2] verify: document corner cases

[Ryan McElroy]

On 3/30/17 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 17b41390f4912a4c18538d778837bc2cf4a1be92
> # Parent  dea2a17cbfd00bf08ee87b3e44b1c71499189f89
> # Available At https://urldefense.proofpoint.com/v2/url?u=https-3A__bitbucket.org_quark-2Dzju_hg-2Ddraft&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=Jw8rundaE7TbmqBYd1txIQ&m=kuj9GJXY5gbugZhlyrbxjthYrYkZ6M3HZHYFrfQg_ZY&s=yj22qlE05uO47PYA0xtQ2kgE_-D5kRIk7mybLrSUZdg&e=
> #              hg pull https://urldefense.proofpoint.com/v2/url?u=https-3A__bitbucket.org_quark-2Dzju_hg-2Ddraft&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=Jw8rundaE7TbmqBYd1txIQ&m=kuj9GJXY5gbugZhlyrbxjthYrYkZ6M3HZHYFrfQg_ZY&s=yj22qlE05uO47PYA0xtQ2kgE_-D5kRIk7mybLrSUZdg&e=  -r 17b41390f491
> 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 does not reflect the actual behavior of the current
> code.
>
> diff --git a/mercurial/verify.py b/mercurial/verify.py
> --- a/mercurial/verify.py
> +++ b/mercurial/verify.py
> @@ -380,5 +380,51 @@ class verifier(object):
>                           del filenodes[f][n]
>   
> -                # verify contents
> +                # Verify contents. 4 cases to care about:
> +                #
> +                #   common: the most common case
> +                #   rename: with a rename
> +                #   meta: file content starts with b'\1\n', the metadata
> +                #         header defined in filelog.py, but without a rename
> +                #   ext: largefiles. content stored elsewhere
> +                #
> +                # More formally, their differences are shown below:
> +                #
> +                #                       | common | rename | meta  | ext
> +                #  -------------------------------------------------------
> +                #   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 could be different from them.
> +                # "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))
>
This comment is very clear to me now. Well done and thanks!