trydiff: extract function that generates filename pairs The code that identifies copies/renames, as well as the filenames before and after, is now isolated and we can extract it to a function so it can be overridden by extensions (in particular the narrow clone extension).

trydiff: read file data in only one place This moves getfilectx() out of the initial block in the loop, leaving that block to be only about finding pairs of filenames in ctx1 and ctx2 to diff.

trydiff: set filename variables to None even when not opts.git or losedatafn There is not much left of the first block "if opts.git or losedatafn" block now. The next patch will move the call to getfilectx() out of that block. We will then be using the defined-ness of 'f1' to tell whether the file existed in ctx1 (and under what name). We will need this information whether or not opts.git or losedatafn was set, so just remove that guard. The only operation in the block that is not cheap is the call to getfilectx(), but that has an extra 'if opts.git' guard already. --ignore-space-change proves that only 'if opts.git or losedatafn:' was removed.

trydiff: read flags in one place Now that we can trust f1/f2 to indicate whether that side of the diff exists, we can move the calls to ctx.flag() to a single place.

trydiff: break 'if opts.git or losedatafn' into two This moves the initialization 'binary' closer to its other assignment, but exists mostly to simplify future patches.

trydiff: make filenames None when they don't exist f1 and f2 are currently set always set to some filename, even for added or deleted files. Let's instead set them to None to indicate that one side of the diff doesn't exist. This lets us use the filename variables instead of the content variables and simplify a bit since the empty string is not a valid filename. More importantly, it paves the way for further simplifications.