Redundant annotation handling in prettyprinter's renderLazy

[sjakobi]

If the annotation handling with (pure mempty) has a performance cost, we should probably try to get rid of it.

prettyprinter/prettyprinter/src/Data/Text/Prettyprint/Doc/Render/Text.hs

Lines 58 to 59 in a03a2bf

	renderLazy :: SimpleDocStream ann -> TL.Text
	renderLazy = TLB.toLazyText . renderSimplyDecorated TLB.fromText (pure mempty) (pure mempty)

prettyprinter/prettyprinter/src/Data/Text/Prettyprint/Doc/Render/Util/StackMachine.hs

Lines 66 to 84 in a03a2bf

	renderSimplyDecorated
	:: Monoid out
	=> (Text -> out) -- ^ Render plain 'Text'
	-> (ann -> out) -- ^ How to render an annotation
	-> (ann -> out) -- ^ How to render the removed annotation
	-> SimpleDocStream ann
	-> out
	renderSimplyDecorated text push pop = go []
	where
	go _ SFail = panicUncaughtFail
	go [] SEmpty = mempty
	go (_:_) SEmpty = panicInputNotFullyConsumed
	go stack (SChar c rest) = text (T.singleton c) <> go stack rest
	go stack (SText _l t rest) = text t <> go stack rest
	go stack (SLine i rest) = text (T.singleton '\n') <> text (textSpaces i) <> go stack rest
	go stack (SAnnPush ann rest) = push ann <> go (ann : stack) rest
	go (ann:stack) (SAnnPop rest) = pop ann <> go stack rest
	go [] SAnnPop{} = panicUnpairedPop
	{-# INLINE renderSimplyDecorated #-}

[sjakobi]

I've had a brief look at the Core and couldn't find any sign of concatenating empty Text blobs. I noticed that we still do all the annotation stack handling though, which probably causes unnecessary allocations. We might want to try getting rid of that.