extdiff: drop the command alias without options example in the help text In the dropped example, the extension would look for 'vdiff.diffargs' in the configuration, and not finding it, would run kdiff3 without the configured options. That's not obvious to a new user who sees a kdiff3 configuration in the prepackaged mergetools.rc file, and sees that kdiff3 still runs. While it is conceivable that the user wants a kdiff3 command that runs without the preconfigured options, it is more likely what they want is this, which uses the canned options: [alias] vdiff = kdiff3 [extdiff] kdiff3 = We could mention alias here, but that seems like it belongs elswhere.

extdiff: allow a preconfigured merge-tool to be invoked There are three ways to configure an extdiff tool: 1) cmd.tool = (/path/to/exe optional) 2) tool = (path/to/exe optional) 3) tool = sometool someargs Previously, if no executable is specified in the first two forms, the named tool must be in $PATH, or the invocation fails. Since the [merge-tools] section already has the path to the diff executable, and/or the registry keys to find the executable on Windows, reuse that configuration for forms 1 and 2 instead of failing. We already fallback to [diff-tools] and then [merge-tools] for program arguments if they aren't specified in the [extdiff] section. Since this additional lookup only occurs if an executable is not on the $PATH for the named tool, this is backwards compatible. For now, we assume the user knows what he is doing if a path is provided. This change allows a configuration file like this (assuming beyondcompare3 is configured in merge-tools), instead of hardcoding system specific a path: [extdiff] beyondcompare3 =

extdiff: sort files when snapshotting This fixes output stability and is generally filesystem-performance-friendly.

filemerge: split the logic for finding an external tool to its own function This will be used by extdiff in an subsequent patch.