RE: [PATCH v5] Enable auto-merge for meld to follow the vim-diff beharior

[<lin.sun@zoom.us>]

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Hi Danh,

Thank you for your comments, and changes apply to the last patch with your suggestions. Please refer the attachment for [PATH v6].
Thank you.

Regards
Lin 

-----Original Message-----
From: Đoàn Trần Công Danh <congdanhqx@gmail.com> 
Sent: Wednesday, July 1, 2020 22:18
To: sunlin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org; sunlin <sunlin7@yahoo.com>; Lin Sun <lin.sun@zoom.us>
Subject: Re: [PATCH v5] Enable auto-merge for meld to follow the vim-diff beharior

On 2020-07-01 07:06:46+0000, sunlin via GitGitGadget <gitgitgadget@gmail.com> wrote:
> From: Lin Sun <lin.sun@zoom.us>
> 
> Make the mergetool used with "meld" backend behave similarly to how 
> "vimdiff" behavior by telling it to auto-merge parts without conflicts 
> and highlight the parts with conflicts when configuring 
> `mergetool.meld.hasAutoMerge` with `true`, or `auto` for automatically 
> detecting the option.
> 
> Signed-off-by: Lin Sun <lin.sun@zoom.us>
> ---
> diff --git a/Documentation/config/mergetool.txt 
> b/Documentation/config/mergetool.txt
> index 09ed31dbfa..9a74bd98dc 100644
> --- a/Documentation/config/mergetool.txt
> +++ b/Documentation/config/mergetool.txt
> @@ -30,6 +30,14 @@ mergetool.meld.hasOutput::
>  	to `true` tells Git to unconditionally use the `--output` option,
>  	and `false` avoids using `--output`.
>  
> +mergetool.meld.hasAutoMerge::
> +	Older versions of `meld` do not support the `--auto-merge` option.
> +	Setting `mergetool.meld.hasOutput` to `true` tells Git to

s/hasOutput/hasAutoMerge/

Bikeshed opinion: I don't know if hasAutoMerge is a good name :)

> +	unconditionally use the `--auto-merge` option, and `false` avoids using
> +	`--auto-merge`, and `auto` detect whether `meld` supports `--auto-merge`
> +	by inspecting the output of `meld --help`, otherwise, follow meld's
> +	default behavior.
> +
>  mergetool.keepBackup::
>  	After performing a merge, the original file with conflict markers
>  	can be saved as a file with a `.orig` extension.  If this variable 
> diff --git a/mergetools/meld b/mergetools/meld index 
> 7a08470f88..9ee835b1e5 100644
> --- a/mergetools/meld
> +++ b/mergetools/meld
> @@ -3,34 +3,74 @@ diff_cmd () {
>  }
>  
>  merge_cmd () {
> -	if test -z "${meld_has_output_option:+set}"
> +	check_meld_for_features
> +
> +	option_auto_merge=
> +	if test "$meld_has_auto_merge_option" = true
>  	then
> -		check_meld_for_output_version
> +		option_auto_merge="--auto-merge"
>  	fi
>  
>  	if test "$meld_has_output_option" = true
>  	then
> -		"$merge_tool_path" --output="$MERGED" \
> +		"$merge_tool_path" $option_auto_merge --output="$MERGED" \
>  			"$LOCAL" "$BASE" "$REMOTE"
>  	else
> -		"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
> +		"$merge_tool_path" $option_auto_merge "$LOCAL" "$MERGED" "$REMOTE"
>  	fi
>  }
>  
> -# Check whether we should use 'meld --output <file>'
> -check_meld_for_output_version () {
> -	meld_path="$(git config mergetool.meld.path)"
> -	meld_path="${meld_path:-meld}"
> +# Get meld help message
> +get_meld_help_msg () {
> +	meld_path="$(git config mergetool.meld.path || echo meld)"
> +	$meld_path --help 2>&1
> +}

I'm actually prefer this change in 2 separated patches to reduce noise.
But given that mergetool/meld doesn't attract much attention, I don't know.

>  
> -	if meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
> +# Check the features and set flags
> +check_meld_for_features () {
> +	# Check whether we should use 'meld --output <file>'
> +	if test -z "${meld_has_output_option:+set}"
>  	then
> -		: use configured value
> -	elif "$meld_path" --help 2>&1 |
> -		grep -e '--output=' -e '\[OPTION\.\.\.\]' >/dev/null
> +		meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
> +		if test "$meld_has_output_option" = true -o \
> +			"$meld_has_output_option" = false

The coding guideline seems to not like "test -o".
I think it's acceptable in this case since we control its input.
The output is comming out of "git config --bool" anyway, so meld_has_output_option must be either "", "true", or "false"

I think we're better to do this instead:

	if test -n "$meld_has_output_option"
	then
		: use configured output
	else
		: messing with help
	fi

> +		then
> +			: use configured value
> +		else
> +			# treat meld_has_output_option as "auto"
> +			if test -z "$meld_help_msg"
> +			then
> +				meld_help_msg="$(get_meld_help_msg)"
> +			fi

If I were writing this patch, I probably changed get_meld_help_msg to

	init_meld_help_msg () {
		if test -z "$meld_help_msg"
		then
			meld_path="$(git config mergetool.meld.path || echo meld)"
			meld_help_msg=$($meld_path --help 2>&1)
		fi
	}

And call init_meld_help_msg unconditionally here, (and in --auto-merge arm below, maybe other arms in the future).

I'm writing without much thought into this, please take my word with a grain of salt :)

> +}


> +
> +			case "$meld_help_msg" in
> +				*"--output="* | *"[OPTION"???"]"*)

I think Git project prefer aligning case arm with case, IOW, move left 1 TAB.

> +					# old ones mention --output and new ones just say OPTION...
> +					meld_has_output_option=true ;;

It's nice to see this update, good.
The comment is no longer correct, though.
The version 3.20.2 has --output but not OPTIONS.

It's not introduced by your change, but I think it's better to say:

	# All versions that has [OPTIONS???] supports --output

> +				*)
> +					meld_has_output_option=false ;;
> +			esac
> +		fi
> +	fi
> +	# Check whether we should use 'meld --auto-merge ...'
> +	if test -z "${meld_has_auto_merge_option:+set}"
>  	then
> -		: old ones mention --output and new ones just say OPTION...
> -		meld_has_output_option=true
> -	else
> -		meld_has_output_option=false
> +		meld_has_auto_merge_option=$(git config mergetool.meld.hasAutoMerge)
> +		if test "$meld_has_auto_merge_option" = auto

Since we don't canonicallise to bool output of mergetool.meld.hasAutoMerge, I think we would need:

	case "$meld_has_auto_merge_option" in
	[Tt]rue|[Yy]es|[Oo]n)
		meld_has_auto_merge_option=true ;;
	auto)
		: this shenanigan ;;
	esac

But, that's a bit messy. Let's see other's opinions.

> +		then
> +			# testing the "--auto-merge" option only if config is "auto"
> +			if test -z "$meld_help_msg"
> +			then
> +					meld_help_msg="$(get_meld_help_msg)"
> +			fi
> +
> +			case "$meld_help_msg" in
> +				*"--auto-merge"*)
> +					: old ones mention --output and new ones just say OPTION...

This comment doesn't apply here.

> +					meld_has_auto_merge_option=true ;;
> +				*)
> +					meld_has_auto_merge_option=false ;;
> +			esac
> +		fi
>  	fi
>  }
> 
> base-commit: 07d8ea56f2ecb64b75b92264770c0a664231ce17
> --
> gitgitgadget

--
Danh

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From 33968fb9e52a6ead7b9fc64943d4c82c3f893865 Mon Sep 17 00:00:00 2001
From: Lin Sun <lin.sun@zoom.us>
Date: Thu, 7 May 2020 07:31:14 +0800
Subject: [PATCH] Enable auto-merge for meld to follow the vim-diff beharior
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Make the mergetool used with "meld" backend behave similarly to
how "vimdiff" behavior by telling it to auto-merge parts without
conflicts and highlight the parts with conflicts when configuring
`mergetool.meld.hasAutoMerge` with `true`, or `auto` for
automatically detecting the option.

Helped-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Lin Sun <lin.sun@zoom.us>
---
 Documentation/config/mergetool.txt |  8 ++++
 mergetools/meld                    | 80 ++++++++++++++++++++++++++++++--------
 2 files changed, 72 insertions(+), 16 deletions(-)

diff --git a/Documentation/config/mergetool.txt b/Documentation/config/mergetool.txt
index 09ed31d..d2af88c 100644
--- a/Documentation/config/mergetool.txt
+++ b/Documentation/config/mergetool.txt
@@ -30,6 +30,14 @@ mergetool.meld.hasOutput::
 	to `true` tells Git to unconditionally use the `--output` option,
 	and `false` avoids using `--output`.
 
+mergetool.meld.hasAutoMerge::
+	Older versions of `meld` do not support the `--auto-merge` option.
+	Setting `mergetool.meld.hasAutoMerge` to `true` tells Git to
+	unconditionally use the `--auto-merge` option, and `false` avoids using
+	`--auto-merge`, and `auto` detect whether `meld` supports `--auto-merge`
+	by inspecting the output of `meld --help`, otherwise, follow meld's
+	default behavior.
+
 mergetool.keepBackup::
 	After performing a merge, the original file with conflict markers
 	can be saved as a file with a `.orig` extension.  If this variable
diff --git a/mergetools/meld b/mergetools/meld
index 7a08470..c6f499d 100644
--- a/mergetools/meld
+++ b/mergetools/meld
@@ -3,34 +3,82 @@ diff_cmd () {
 }
 
 merge_cmd () {
-	if test -z "${meld_has_output_option:+set}"
+	check_meld_for_features
+
+	option_auto_merge=
+	if test "$meld_has_auto_merge_option" = true
 	then
-		check_meld_for_output_version
+		option_auto_merge="--auto-merge"
 	fi
 
 	if test "$meld_has_output_option" = true
 	then
-		"$merge_tool_path" --output="$MERGED" \
+		"$merge_tool_path" $option_auto_merge --output="$MERGED" \
 			"$LOCAL" "$BASE" "$REMOTE"
 	else
-		"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+		"$merge_tool_path" $option_auto_merge "$LOCAL" "$MERGED" "$REMOTE"
 	fi
 }
 
-# Check whether we should use 'meld --output <file>'
-check_meld_for_output_version () {
-	meld_path="$(git config mergetool.meld.path)"
-	meld_path="${meld_path:-meld}"
+# Get meld help message
+init_meld_help_msg () {
+	if test -z "${meld_help_msg:+set}"
+	then
+		meld_path="$(git config mergetool.meld.path || echo meld)"
+		meld_help_msg=$($meld_path --help 2>&1)
+	fi
+}
 
-	if meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
+# Check the features and set flags
+check_meld_for_features () {
+	# Check whether we should use 'meld --output <file>'
+	if test -z "${meld_has_output_option:+set}"
 	then
-		: use configured value
-	elif "$meld_path" --help 2>&1 |
-		grep -e '--output=' -e '\[OPTION\.\.\.\]' >/dev/null
+		meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
+		case "$meld_has_output_option" in
+		true|false)
+			: use configured value
+			;;
+		*)
+			: treat meld_has_output_option as "auto"
+			init_meld_help_msg
+
+			case "$meld_help_msg" in
+			*"--output="* | *"[OPTION"???"]"*)
+				# All version that has [OPTION???] supports --output
+				meld_has_output_option=true
+				;;
+			*)
+				meld_has_output_option=false
+				;;
+			esac
+			;;
+		esac
+	fi
+	# Check whether we should use 'meld --auto-merge ...'
+	if test -z "${meld_has_auto_merge_option:+set}"
 	then
-		: old ones mention --output and new ones just say OPTION...
-		meld_has_output_option=true
-	else
-		meld_has_output_option=false
+		meld_has_auto_merge_option=$(git config mergetool.meld.hasAutoMerge)
+		case "$meld_has_auto_merge_option" in
+		[Tt]rue|[Yy]es|[Oo]n|1)
+			meld_has_auto_merge_option=true
+			;;
+		auto)
+			# testing the "--auto-merge" option only if config is "auto"
+			init_meld_help_msg
+
+			case "$meld_help_msg" in
+			*"--auto-merge"*)
+				meld_has_auto_merge_option=true
+				;;
+			*)
+				meld_has_auto_merge_option=false
+				;;
+			esac
+			;;
+		*)
+			meld_has_auto_merge_option=false
+			;;
+		esac
 	fi
 }
-- 
2.2.0