Bug with --abbrev option in git log?

Bug with --abbrev option in git log?

[Mário Guimarães]

Hello Git community,

please see next what I believe to be a bug with the  --abbrev option in git log.
If this is not a bug, can someone explain why Git is giving this output?

Thanks
Mário Guimarães

======================================================
Thank you for filling out a Git bug report!
Please answer the following questions to help us understand your issue.

What did you do before the bug happened? (Steps to reproduce your issue)

In the Git repository run this command:

git log --raw -r -c --abbrev=6 --pretty=oneline -n1
a7144d4bc5ab58f306a1e5c73b27196fb999a63d

What did you expect to happen? (Expected behavior)

I was expecting to get this line in the output

::100644 100644 100644 639a41 111378 05ba1d MM Documentation/git-rebase.txt

What happened instead? (Actual behavior)

I got the following line instead

::100644 100644 100644 639a41 111378 05ba1d3 MM Documentation/git-rebase.txt

What's different between what you expected and what actually happened?

Since `--abbrev` is set to 6 the expected hash is `05ba1d` not `05ba1d3`.

Anything else you want to add:

If --abbrev is set to N then the size of all hashes should be the
first N hex digits.

The problem with `--abbrev` is more evident with values below 7. Try with 1, 2,
3, 4, and 5, to see for yourself.

Please review the rest of the bug report below.
You can delete any lines you don't wish to share.


[System Info]
git version:
git version 2.29.2
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Darwin 19.6.0 Darwin Kernel Version 19.6.0: Mon Aug 31 22:12:52
PDT 2020; root:xnu-6153.141.2~1/RELEASE_X86_64 x86_64
compiler info: clang: 12.0.0 (clang-1200.0.32.21)
libc info: no libc information available
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]
======================================================

Re: Bug with --abbrev option in git log?

[Junio C Hamano]

Mário Guimarães  <mario.luis.guimaraes@gmail.com> writes:

> In the Git repository run this command:
>
> git log --raw -r -c --abbrev=6 --pretty=oneline -n1
> a7144d4bc5ab58f306a1e5c73b27196fb999a63d

This is not one of my object, so above won't be usable as
reproduction recipe.  But that is OK.

> What did you expect to happen? (Expected behavior)
>
> I was expecting to get this line in the output
>
> ::100644 100644 100644 639a41 111378 05ba1d MM Documentation/git-rebase.txt
>
> What happened instead? (Actual behavior)
>
> I got the following line instead
>
> ::100644 100644 100644 639a41 111378 05ba1d3 MM Documentation/git-rebase.txt

The above command tells us that you locally have an object whose
name begins with 05ba1d3, which I do not have.  But my history
shared with the entire world has an object whose name begins with
05ba1d7, and I am reasonably sure that your repository has it, since
it is a part of 17f26a9e (git-am: fix shell quoting, 2009-01-14).

So in my repository, 05ba1d is enough to uniquely identify 05ba1d7,
but in your repository 05ba1d is not enough to uniquely identify
05ba1d3, because 05ba1d7 also exists in your repository.  And when
the object cannot be uniquely specified with the given abbreviation
width, Git makes sure its output is usable to uniquely identify the
object it wants to name.

In short, I think what you observed is totally expected.

The documentation has some room for improvement, I also think.

How about saying something like this?



 Documentation/diff-options.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git i/Documentation/diff-options.txt w/Documentation/diff-options.txt
index ee52b65e46..114e440c5b 100644
--- i/Documentation/diff-options.txt
+++ w/Documentation/diff-options.txt
@@ -446,7 +446,8 @@ endif::git-format-patch[]
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
 	name in diff-raw format output and diff-tree header
-	lines, show only a partial prefix.
+	lines, show only a partial prefix that uses at least '<n>'
+	hexdigits.
 	In diff-patch output format, `--full-index` takes higher
 	precedence, i.e. if `--full-index` is specified, full blob
 	names will be shown regardless of `--abbrev`.

[PATCH] doc: clarify that most --abbrev[=<n>] are about minimum length

[Junio C Hamano]

Early text written in 2006 explains the "--abbrev=<n>" option to
"show only a partial prefix", without saying that the length of the
partial prefix is not necessarily the number given to the option to
ensure that the output names the object uniquely.

Luckily, the text written for "git describe" in 2011 explains that
the output is made to name the object uniquely using at least <n>
hexdigits much clearly.

Model the explanation and update documentation for the diff family
of commands, "blame", "branch --verbose", "ls-files" and "ls-tree".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/diff-options.txt   | 3 ++-
 Documentation/git-blame.txt      | 4 +++-
 Documentation/git-branch.txt     | 8 +++++---
 Documentation/git-ls-files.txt   | 5 +++--
 Documentation/git-ls-tree.txt    | 3 ++-
 Documentation/pretty-options.txt | 3 ++-
 6 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 573fb9bb71..d73fdb8567 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -446,7 +446,8 @@ endif::git-format-patch[]
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
 	name in diff-raw format output and diff-tree header
-	lines, show only a partial prefix.
+	lines, show <n> hexadecimal digits, or as many digits
+	as needed to form a unique object name.
 	In diff-patch output format, `--full-index` takes higher
 	precedence, i.e. if `--full-index` is specified, full blob
 	names will be shown regardless of `--abbrev`.
diff --git a/Documentation/git-blame.txt b/Documentation/git-blame.txt
index 7e81541996..34b496d485 100644
--- a/Documentation/git-blame.txt
+++ b/Documentation/git-blame.txt
@@ -87,7 +87,9 @@ include::blame-options.txt[]
 
 --abbrev=<n>::
 	Instead of using the default 7+1 hexadecimal digits as the
-	abbreviated object name, use <n>+1 digits. Note that 1 column
+	abbreviated object name, use <m>+1 digits, where <m> is at
+	least <n> but ensures the commit object names are unique.
+	Note that 1 column
 	is used for a caret to mark the boundary commit.
 
 
diff --git a/Documentation/git-branch.txt b/Documentation/git-branch.txt
index ace4ad3da8..89611c3959 100644
--- a/Documentation/git-branch.txt
+++ b/Documentation/git-branch.txt
@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git branch' [--color[=<when>] | --no-color] [--show-current]
-	[-v [--abbrev=<length> | --no-abbrev]]
+	[-v [--abbrev=<n> | --no-abbrev]]
 	[--column[=<options>] | --no-column] [--sort=<key>]
 	[--merged [<commit>]] [--no-merged [<commit>]]
 	[--contains [<commit>]] [--no-contains [<commit>]]
@@ -194,8 +194,10 @@ This option is only applicable in non-verbose mode.
 	Be more quiet when creating or deleting a branch, suppressing
 	non-error messages.
 
---abbrev=<length>::
-	Alter the sha1's minimum display length in the output listing.
+--abbrev=<n>::
+	In the verbose listing that show the commit object name,
+	use <n>, or as many hexdigits as needed to form a unique
+	object name.
 	The default value is 7 and can be overridden by the `core.abbrev`
 	config option.
 
diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
index 3cb2ebb438..60e3063fed 100644
--- a/Documentation/git-ls-files.txt
+++ b/Documentation/git-ls-files.txt
@@ -19,7 +19,7 @@ SYNOPSIS
 		[--exclude-standard]
 		[--error-unmatch] [--with-tree=<tree-ish>]
 		[--full-name] [--recurse-submodules]
-		[--abbrev] [--] [<file>...]
+		[--abbrev[=<n>]] [--] [<file>...]
 
 DESCRIPTION
 -----------
@@ -153,7 +153,8 @@ a space) at the start of each line:
 
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
-	lines, show only a partial prefix.
+	lines, show <n>, or as many hexadecimal digits
+	as needed, to form a unique object name.
 	Non default number of digits can be specified with --abbrev=<n>.
 
 --debug::
diff --git a/Documentation/git-ls-tree.txt b/Documentation/git-ls-tree.txt
index a7515714da..480c668d0f 100644
--- a/Documentation/git-ls-tree.txt
+++ b/Documentation/git-ls-tree.txt
@@ -62,7 +62,8 @@ OPTIONS
 
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
-	lines, show only a partial prefix.
+	lines, show <n>, or as many hexadecimal digits
+	as needed, to form a unique object name.
 	Non default number of digits can be specified with --abbrev=<n>.
 
 --full-name::
diff --git a/Documentation/pretty-options.txt b/Documentation/pretty-options.txt
index 17c5aac4b7..da6ab0de0c 100644
--- a/Documentation/pretty-options.txt
+++ b/Documentation/pretty-options.txt
@@ -16,7 +16,8 @@ configuration (see linkgit:git-config[1]).
 
 --abbrev-commit::
 	Instead of showing the full 40-byte hexadecimal commit object
-	name, show only a partial prefix.  Non default number of
+	name, show only a partial prefix that names the object uniquely.
+	Non default number of
 	digits can be specified with "--abbrev=<n>" (which also modifies
 	diff output, if it is displayed).
 +
-- 
2.29.2-287-gba574db674

Re: [PATCH] doc: clarify that most --abbrev[=<n>] are about minimum length

[Derrick Stolee]

On 11/3/2020 8:44 PM, Junio C Hamano wrote:
> Early text written in 2006 explains the "--abbrev=<n>" option to
> "show only a partial prefix", without saying that the length of the
> partial prefix is not necessarily the number given to the option to
> ensure that the output names the object uniquely.
> 
> Luckily, the text written for "git describe" in 2011 explains that
> the output is made to name the object uniquely using at least <n>
> hexdigits much clearly.
> 
> Model the explanation and update documentation for the diff family
> of commands, "blame", "branch --verbose", "ls-files" and "ls-tree".

Thanks for being thorough here! Your patch is already an
improvement on what we have. I hope that my suggestions
below help to improve it further.

> --- a/Documentation/diff-options.txt
> +++ b/Documentation/diff-options.txt
> @@ -446,7 +446,8 @@ endif::git-format-patch[]
>  --abbrev[=<n>]::
>  	Instead of showing the full 40-byte hexadecimal object
>  	name in diff-raw format output and diff-tree header
> -	lines, show only a partial prefix.
> +	lines, show <n> hexadecimal digits, or as many digits
> +	as needed to form a unique object name.

A reoccurring theme in this patch is that the --abbrev option
provides a lower bound, even if fewer digits are needed for a
unique object name. Using these two phrases with an "or" has
some ambiguity about which is chosen.

Perhaps we should try to describe it as "<n> is the default,
but can grow as needed". Here is an attempt:

-	lines, show only a partial prefix.
+	lines, show at least <n> hexadecimal digits, increasing the
+	prefix length as needed to uniquely identify an object.

If you prefer wording like this, then there are a few very
similar snippets later in git-branch.txt and git-ls-files.txt.

> --- a/Documentation/git-blame.txt
> +++ b/Documentation/git-blame.txt
> @@ -87,7 +87,9 @@ include::blame-options.txt[]
>  
>  --abbrev=<n>::
>  	Instead of using the default 7+1 hexadecimal digits as the
> -	abbreviated object name, use <n>+1 digits. Note that 1 column
> +	abbreviated object name, use <m>+1 digits, where <m> is at
> +	least <n> but ensures the commit object names are unique.
> +	Note that 1 column
>  	is used for a caret to mark the boundary commit.

This captures the "at least <n>" pretty well, especially considering
the complications around "+1".

> ---abbrev=<length>::
> -	Alter the sha1's minimum display length in the output listing.
> +--abbrev=<n>::
> +	In the verbose listing that show the commit object name,
> +	use <n>, or as many hexdigits as needed to form a unique
> +	object name.

Adapting from your wording here made me think that this might
be a simpler way to phrase it:

+--abbrev=<n>::
+	In the verbose listing that show the commit object name,
+	use at least <n> hexdigits to form a unique object name.

> diff --git a/Documentation/pretty-options.txt b/Documentation/pretty-options.txt
> index 17c5aac4b7..da6ab0de0c 100644
> --- a/Documentation/pretty-options.txt
> +++ b/Documentation/pretty-options.txt
> @@ -16,7 +16,8 @@ configuration (see linkgit:git-config[1]).
>  
>  --abbrev-commit::
>  	Instead of showing the full 40-byte hexadecimal commit object
> -	name, show only a partial prefix.  Non default number of
> +	name, show only a partial prefix that names the object uniquely.

Perhaps "show a prefix that uniquely identifies the object" ?

> +	Non default number of
>  	digits can be specified with "--abbrev=<n>" (which also modifies
>  	diff output, if it is displayed).

I know this is in the existing docs, but this last sentence should
probably start with "A non-default number of digits..." Alternatively,
we could rephrase the entire thing to use more active voice:

+ The `--abbrev=<n>` option modifies the minimum number of digits
+ for these prefixes, including objects reported in displayed diff
+ output.

Thanks,
-Stolee

[PATCH v2] doc: clarify that --abbrev=<n> is about the minimum length

[Junio C Hamano]

Early text written in 2006 explains the "--abbrev=<n>" option to
"show only a partial prefix", without saying that the length of the
partial prefix is not necessarily the number given to the option to
ensure that the output names the object uniquely.

Update documentation for the diff family of commands, "blame",
"branch --verbose", "ls-files" and "ls-tree" to stress that the
short prefix must uniquely refer to an object, and <n> is merely
the mininum number of hexdigits used in the prefix.

Helped-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * Thanks for your suggestion.  I decided to use "the shortest
   prefix that is at least <n> hexdigits long".


Range-diff:
1:  01c62c8d6f ! 1:  4f8524079c doc: clarify that most --abbrev[=<n>] are about minimum length
    @@ Metadata
     Author: Junio C Hamano <gitster@pobox.com>
     
      ## Commit message ##
    -    doc: clarify that most --abbrev[=<n>] are about minimum length
    +    doc: clarify that --abbrev=<n> is about the minimum length
     
         Early text written in 2006 explains the "--abbrev=<n>" option to
         "show only a partial prefix", without saying that the length of the
         partial prefix is not necessarily the number given to the option to
         ensure that the output names the object uniquely.
     
    -    Luckily, the text written for "git describe" in 2011 explains that
    -    the output is made to name the object uniquely using at least <n>
    -    hexdigits much clearly.
    -
    -    Model the explanation and update documentation for the diff family
    -    of commands, "blame", "branch --verbose", "ls-files" and "ls-tree".
    +    Update documentation for the diff family of commands, "blame",
    +    "branch --verbose", "ls-files" and "ls-tree" to stress that the
    +    short prefix must uniquely refer to an object, and <n> is merely
    +    the mininum number of hexdigits used in the prefix.
     
    +    Helped-by: Derrick Stolee <dstolee@microsoft.com>
         Signed-off-by: Junio C Hamano <gitster@pobox.com>
     
      ## Documentation/diff-options.txt ##
    @@ Documentation/diff-options.txt: endif::git-format-patch[]
      	Instead of showing the full 40-byte hexadecimal object
      	name in diff-raw format output and diff-tree header
     -	lines, show only a partial prefix.
    -+	lines, show <n> hexadecimal digits, or as many digits
    -+	as needed to form a unique object name.
    ++	lines, show the shortest prefix that is at least '<n>'
    ++	hexdigits long that uniquely refers the object.
      	In diff-patch output format, `--full-index` takes higher
      	precedence, i.e. if `--full-index` is specified, full blob
      	names will be shown regardless of `--abbrev`.
    @@ Documentation/git-branch.txt: This option is only applicable in non-verbose mode
     -	Alter the sha1's minimum display length in the output listing.
     +--abbrev=<n>::
     +	In the verbose listing that show the commit object name,
    -+	use <n>, or as many hexdigits as needed to form a unique
    -+	object name.
    ++	show the shortest prefix that is at least '<n>' hexdigits
    ++	long that uniquely refers the object.
      	The default value is 7 and can be overridden by the `core.abbrev`
      	config option.
      
    @@ Documentation/git-ls-files.txt: a space) at the start of each line:
      --abbrev[=<n>]::
      	Instead of showing the full 40-byte hexadecimal object
     -	lines, show only a partial prefix.
    -+	lines, show <n>, or as many hexadecimal digits
    -+	as needed, to form a unique object name.
    ++	lines, show the shortest prefix that is at least '<n>'
    ++	hexdigits long that uniquely refers the object.
      	Non default number of digits can be specified with --abbrev=<n>.
      
      --debug::
    @@ Documentation/git-ls-tree.txt: OPTIONS
      --abbrev[=<n>]::
      	Instead of showing the full 40-byte hexadecimal object
     -	lines, show only a partial prefix.
    -+	lines, show <n>, or as many hexadecimal digits
    -+	as needed, to form a unique object name.
    ++	lines, show the shortest prefix that is at least '<n>'
    ++	hexdigits long that uniquely refers the object.
      	Non default number of digits can be specified with --abbrev=<n>.
      
      --full-name::
    @@ Documentation/pretty-options.txt: configuration (see linkgit:git-config[1]).
      --abbrev-commit::
      	Instead of showing the full 40-byte hexadecimal commit object
     -	name, show only a partial prefix.  Non default number of
    -+	name, show only a partial prefix that names the object uniquely.
    -+	Non default number of
    - 	digits can be specified with "--abbrev=<n>" (which also modifies
    - 	diff output, if it is displayed).
    +-	digits can be specified with "--abbrev=<n>" (which also modifies
    +-	diff output, if it is displayed).
    ++	name, show a prefix that names the object uniquely.
    ++	"--abbrev=<n>" (which also modifies diff output, if it is displayed)
    ++	option can be used to specify the minimum length of the prefix.
      +
    + This should make "--pretty=oneline" a whole lot more readable for
    + people using 80-column terminals.

 Documentation/diff-options.txt   | 3 ++-
 Documentation/git-blame.txt      | 4 +++-
 Documentation/git-branch.txt     | 8 +++++---
 Documentation/git-ls-files.txt   | 5 +++--
 Documentation/git-ls-tree.txt    | 3 ++-
 Documentation/pretty-options.txt | 6 +++---
 6 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 573fb9bb71..706c69bc82 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -446,7 +446,8 @@ endif::git-format-patch[]
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
 	name in diff-raw format output and diff-tree header
-	lines, show only a partial prefix.
+	lines, show the shortest prefix that is at least '<n>'
+	hexdigits long that uniquely refers the object.
 	In diff-patch output format, `--full-index` takes higher
 	precedence, i.e. if `--full-index` is specified, full blob
 	names will be shown regardless of `--abbrev`.
diff --git a/Documentation/git-blame.txt b/Documentation/git-blame.txt
index 7e81541996..34b496d485 100644
--- a/Documentation/git-blame.txt
+++ b/Documentation/git-blame.txt
@@ -87,7 +87,9 @@ include::blame-options.txt[]
 
 --abbrev=<n>::
 	Instead of using the default 7+1 hexadecimal digits as the
-	abbreviated object name, use <n>+1 digits. Note that 1 column
+	abbreviated object name, use <m>+1 digits, where <m> is at
+	least <n> but ensures the commit object names are unique.
+	Note that 1 column
 	is used for a caret to mark the boundary commit.
 
 
diff --git a/Documentation/git-branch.txt b/Documentation/git-branch.txt
index ace4ad3da8..adaa1782a8 100644
--- a/Documentation/git-branch.txt
+++ b/Documentation/git-branch.txt
@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git branch' [--color[=<when>] | --no-color] [--show-current]
-	[-v [--abbrev=<length> | --no-abbrev]]
+	[-v [--abbrev=<n> | --no-abbrev]]
 	[--column[=<options>] | --no-column] [--sort=<key>]
 	[--merged [<commit>]] [--no-merged [<commit>]]
 	[--contains [<commit>]] [--no-contains [<commit>]]
@@ -194,8 +194,10 @@ This option is only applicable in non-verbose mode.
 	Be more quiet when creating or deleting a branch, suppressing
 	non-error messages.
 
---abbrev=<length>::
-	Alter the sha1's minimum display length in the output listing.
+--abbrev=<n>::
+	In the verbose listing that show the commit object name,
+	show the shortest prefix that is at least '<n>' hexdigits
+	long that uniquely refers the object.
 	The default value is 7 and can be overridden by the `core.abbrev`
 	config option.
 
diff --git a/Documentation/git-ls-files.txt b/Documentation/git-ls-files.txt
index 3cb2ebb438..cbcf5263dd 100644
--- a/Documentation/git-ls-files.txt
+++ b/Documentation/git-ls-files.txt
@@ -19,7 +19,7 @@ SYNOPSIS
 		[--exclude-standard]
 		[--error-unmatch] [--with-tree=<tree-ish>]
 		[--full-name] [--recurse-submodules]
-		[--abbrev] [--] [<file>...]
+		[--abbrev[=<n>]] [--] [<file>...]
 
 DESCRIPTION
 -----------
@@ -153,7 +153,8 @@ a space) at the start of each line:
 
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
-	lines, show only a partial prefix.
+	lines, show the shortest prefix that is at least '<n>'
+	hexdigits long that uniquely refers the object.
 	Non default number of digits can be specified with --abbrev=<n>.
 
 --debug::
diff --git a/Documentation/git-ls-tree.txt b/Documentation/git-ls-tree.txt
index a7515714da..db02d6d79a 100644
--- a/Documentation/git-ls-tree.txt
+++ b/Documentation/git-ls-tree.txt
@@ -62,7 +62,8 @@ OPTIONS
 
 --abbrev[=<n>]::
 	Instead of showing the full 40-byte hexadecimal object
-	lines, show only a partial prefix.
+	lines, show the shortest prefix that is at least '<n>'
+	hexdigits long that uniquely refers the object.
 	Non default number of digits can be specified with --abbrev=<n>.
 
 --full-name::
diff --git a/Documentation/pretty-options.txt b/Documentation/pretty-options.txt
index 17c5aac4b7..27ddaf84a1 100644
--- a/Documentation/pretty-options.txt
+++ b/Documentation/pretty-options.txt
@@ -16,9 +16,9 @@ configuration (see linkgit:git-config[1]).
 
 --abbrev-commit::
 	Instead of showing the full 40-byte hexadecimal commit object
-	name, show only a partial prefix.  Non default number of
-	digits can be specified with "--abbrev=<n>" (which also modifies
-	diff output, if it is displayed).
+	name, show a prefix that names the object uniquely.
+	"--abbrev=<n>" (which also modifies diff output, if it is displayed)
+	option can be used to specify the minimum length of the prefix.
 +
 This should make "--pretty=oneline" a whole lot more readable for
 people using 80-column terminals.
-- 
2.29.2-287-gba574db674

Re: [PATCH v2] doc: clarify that --abbrev=<n> is about the minimum length

[Derrick Stolee]

On 11/4/20 5:01 PM, Junio C Hamano wrote:
> Early text written in 2006 explains the "--abbrev=<n>" option to
> "show only a partial prefix", without saying that the length of the
> partial prefix is not necessarily the number given to the option to
> ensure that the output names the object uniquely.
> 
> Update documentation for the diff family of commands, "blame",
> "branch --verbose", "ls-files" and "ls-tree" to stress that the
> short prefix must uniquely refer to an object, and <n> is merely
> the mininum number of hexdigits used in the prefix.
> 
> Helped-by: Derrick Stolee <dstolee@microsoft.com>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> 
>  * Thanks for your suggestion.  I decided to use "the shortest
>    prefix that is at least <n> hexdigits long".

I like this version. Thanks!

-Stolee

Re: Bug with --abbrev option in git log?

[Mário Guimarães]

Hello

Junio C Hamano <gitster@pobox.com> escreveu no dia quarta, 4/11/2020 à(s) 01:12:
>
> Mário Guimarães  <mario.luis.guimaraes@gmail.com> writes:
>
> > In the Git repository run this command:
> >
> > git log --raw -r -c --abbrev=6 --pretty=oneline -n1
> > a7144d4bc5ab58f306a1e5c73b27196fb999a63d
>
> This is not one of my object, so above won't be usable as
> reproduction recipe.  But that is OK.
>
> > What did you expect to happen? (Expected behavior)
> >
> > I was expecting to get this line in the output
> >
> > ::100644 100644 100644 639a41 111378 05ba1d MM Documentation/git-rebase.txt
> >
> > What happened instead? (Actual behavior)
> >
> > I got the following line instead
> >
> > ::100644 100644 100644 639a41 111378 05ba1d3 MM Documentation/git-rebase.txt
>
> The above command tells us that you locally have an object whose
> name begins with 05ba1d3, which I do not have.  But my history
> shared with the entire world has an object whose name begins with
> 05ba1d7, and I am reasonably sure that your repository has it, since
> it is a part of 17f26a9e (git-am: fix shell quoting, 2009-01-14).
>
> So in my repository, 05ba1d is enough to uniquely identify 05ba1d7,
> but in your repository 05ba1d is not enough to uniquely identify
> 05ba1d3, because 05ba1d7 also exists in your repository.  And when
> the object cannot be uniquely specified with the given abbreviation
> width, Git makes sure its output is usable to uniquely identify the
> object it wants to name.
>
> In short, I think what you observed is totally expected.
>
> The documentation has some room for improvement, I also think.
>
> How about saying something like this?
>
>
>
>  Documentation/diff-options.txt | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git i/Documentation/diff-options.txt w/Documentation/diff-options.txt
> index ee52b65e46..114e440c5b 100644
> --- i/Documentation/diff-options.txt
> +++ w/Documentation/diff-options.txt
> @@ -446,7 +446,8 @@ endif::git-format-patch[]
>  --abbrev[=<n>]::
>         Instead of showing the full 40-byte hexadecimal object
>         name in diff-raw format output and diff-tree header
> -       lines, show only a partial prefix.
> +       lines, show only a partial prefix that uses at least '<n>'
> +       hexdigits.
>         In diff-patch output format, `--full-index` takes higher
>         precedence, i.e. if `--full-index` is specified, full blob
>         names will be shown regardless of `--abbrev`.

What about this? It makes clear that the prefix is still one that can
be used to identify the object in the repository.

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index ee52b65e46..c15b4adb28 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -446,8 +446,9 @@ endif::git-format-patch[]
 --abbrev[=<n>]::
        Instead of showing the full 40-byte hexadecimal object
        name in diff-raw format output and diff-tree header
-       lines, show only a partial prefix.
-       In diff-patch output format, `--full-index` takes higher
+       lines, show only the minimal prefix that identifies
+       the object using at least `<n>` hexdigits.
        In diff-patch output format, `--full-index` takes higher
        precedence, i.e. if `--full-index` is specified, full blob
        names will be shown regardless of `--abbrev`.
        Non default number of digits can be specified with `--abbrev=<n>`.