narrow: add server logic to send cg while widening without ellipsis Before this patch, if you try to widen a narrow clone without ellipsis enabled, it will be broken and the exchange.pull() done by tracked command to widen the clone will be no-op because no custom logic exists for this and server sees that we have all csets and it says `no changes found`. The widening with ellipsis send KILL for existing changegroups and send new changegroups because of the change in ellipsis hash, but we can prevent that in non-ellipsis cases. This patch adds server side logic to send the changegroups for the changesets which are on the client again with filelogs and manifests for the new includes. This is a very starting implementation and we send changegroups and manifests too while we can prevent them. Following things can definitely be improved in the logic this patch adds: 1) Send just the filelogs and treemanifests 2) Send the filelogs only for the additions in the include I tried 1) here but the code is coupled tightly and the way I was able to do that was hacking into the changegroup generation code in a very dirty way, like adding conditionals and preventing the yield. This patch also adds a 'widen' kwarg to prevent other commands except widening to go through that codepath. The test changes demonstrate that the new implementation is correct and fixes things. Differential Revision: https://phab.mercurial-scm.org/D4383

tests: add test to show widening is broken without ellipsis This patch adds a test to show that widening a narrow clone is broken if ellipsis is disabled. I don't think I can add cases to existing test-narrow-widen.t and check-in a failing version of that. So I created a copy. Once the test is fixed, we can merge this new test file back into the original one using testcases. Also, this is just testing treemanifest case because having two cases and both or are failing with different outputs is a bit hard to manage. This is important because upcoming patches will try to fix the broken part. Differential Revision: https://phab.mercurial-scm.org/D4382

stringutil: emit multiple chunks when pretty printing This avoids concatenating output inside pprintgen() itself. But the real reason for this is it will make it easier to add indentation, as we'll need to account for indentation when emitting each individual object in a collection. The verbosity of this code compared to the original is a bit unfortunate. But I suppose this is the price to pay for having nice things (streaming and indenting). We could probably abstract the "print a collection" bits into a generic function to avoid some duplication. But I'm not overly inclined to do this. Differential Revision: https://phab.mercurial-scm.org/D4398