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

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>
---
    Enable auto-merge for meld to follow the vimdiff beharior
    
    Hi, the mergetool "meld" does NOT merge the no-conflict changes, while
    the mergetool "vimdiff" will merge the no-conflict changes and highlight
    the conflict parts. This patch will make the mergetool "meld" similar to
    "vimdiff", auto-merge the no-conflict changes, highlight conflict parts.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-781%2Fsunlin7%2Fmaster-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-781/sunlin7/master-v5
Pull-Request: https://github.com/git/git/pull/781

Range-diff vs v4:

 1:  93ae3ec011 ! 1:  344817d579 Enable auto-merge for meld to follow the vim-diff beharior
     @@
       ## Metadata ##
     -Author: lin.sun <lin.sun@zoom.us>
     +Author: Lin Sun <lin.sun@zoom.us>
      
       ## Commit message ##
          Enable auto-merge for meld to follow the vim-diff beharior
      
          Make the mergetool used with "meld" backend behave similarly to
     -    how "vimdiff" beheaves by telling it to auto-merge parts without
     -    conflicts and highlight the parts with conflicts.
     +    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>
     +    Signed-off-by: Lin Sun <lin.sun@zoom.us>
     +
     + ## Documentation/config/mergetool.txt ##
     +@@ Documentation/config/mergetool.txt: 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
     ++	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
      
       ## mergetools/meld ##
      @@ mergetools/meld: diff_cmd () {
     @@ mergetools/meld: diff_cmd () {
      +# Get meld help message
      +get_meld_help_msg () {
      +	meld_path="$(git config mergetool.meld.path || echo meld)"
     -+  $meld_path --help 2>&1
     ++	$meld_path --help 2>&1
      +}
       
      -	if meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
     @@ mergetools/meld: diff_cmd () {
      -		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 \
     -+						"$meld_has_output_option" = false
     ++			"$meld_has_output_option" = false
      +		then
      +			: use configured value
     -+		else												# treat meld_has_output_option as "auto"
     ++		else
     ++			# treat meld_has_output_option as "auto"
      +			if test -z "$meld_help_msg"
      +			then
      +				meld_help_msg="$(get_meld_help_msg)"
      +			fi
      +
     -+			if echo "$meld_help_msg" |
     -+							grep -e '--output=' -e '\[OPTION\.\.\.\]' >/dev/null
     -+			then
     -+				: old ones mention --output and new ones just say OPTION...
     -+				meld_has_output_option=true
     -+			else
     -+				meld_has_output_option=false
     -+			fi
     ++			case "$meld_help_msg" in
     ++				*"--output="* | *"[OPTION"???"]"*)
     ++					# old ones mention --output and new ones just say OPTION...
     ++					meld_has_output_option=true ;;
     ++				*)
     ++					meld_has_output_option=false ;;
     ++			esac
      +		fi
      +	fi
      +	# Check whether we should use 'meld --auto-merge ...'
     @@ mergetools/meld: diff_cmd () {
      -		meld_has_output_option=true
      -	else
      -		meld_has_output_option=false
     -+		meld_has_auto_merge_option=$(git config --bool mergetool.meld.hasAutoMerge)
     -+		if test "$meld_has_auto_merge_option" = true -o \
     -+						"$meld_has_auto_merge_option" = false
     ++		meld_has_auto_merge_option=$(git config mergetool.meld.hasAutoMerge)
     ++		if test "$meld_has_auto_merge_option" = auto
      +		then
     -+			: use configured value
     -+		else												# treat meld_has_auto_merge_option as "auto"
     ++			# 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
      +
     -+			if echo "$meld_help_msg" | grep -e '--auto-merge' >/dev/null
     -+			then
     -+					meld_has_auto_merge_option=true
     -+			else
     -+				meld_has_auto_merge_option=false
     -+			fi
     ++			case "$meld_help_msg" in
     ++				*"--auto-merge"*)
     ++					: old ones mention --output and new ones just say OPTION...
     ++					meld_has_auto_merge_option=true ;;
     ++				*)
     ++					meld_has_auto_merge_option=false ;;
     ++			esac
      +		fi
       	fi
       }

 Documentation/config/mergetool.txt |  8 ++++
 mergetools/meld                    | 72 +++++++++++++++++++++++-------
 2 files changed, 64 insertions(+), 16 deletions(-)