Temporary buffers are now created without extension. That doesn't allow difft to guess what language should be used (i.e., when the content of a temporary buffer is second).
A major-mode of a temporary buffer can be check and extension guessed (i.e., extracted from auto-mode-alist). Such a temporary buffer will let difft to make better guesses about a language. At the first look the --languagedifft's argument should be reserved to carry language-override function arguments (i.e., to make it easier to reason what will happen), and still allowing user to override the detection mechanism.
Temporary buffers are now created without extension. That doesn't allow
difftto guess what language should be used (i.e., when the content of a temporary buffer is second).A
major-modeof a temporary buffer can be check and extension guessed (i.e., extracted fromauto-mode-alist). Such a temporary buffer will letdifftto make better guesses about a language. At the first look the--languagedifft's argument should be reserved to carrylanguage-overridefunction arguments (i.e., to make it easier to reason what will happen), and still allowing user to override the detection mechanism.