Printing arguments: short circuiting some cases

[duailibe]

So when investigating #4784, I've managed to verify the issue was in printArgumentsList(), more specifically the part where we check if it should hug the first of the last argument, and later, verified the issue was in the conditionalGroup, and more specifically, the first possible group, with a combination of ifBreak() and softline.

The previous code had the following meaning: if the group breaks, print all arguments broken down; else, just concat the arguments with the wrapping parenthesis (note that there are some cases where we print a new line but the group doesn't break!).

So the first thing I changed was: if none of the arguments break beforehand (this is before printing, so this means the argument "doc" already includes something that makes it break. It can break later when printing if it exceeds the print width), we can try a simple concat. If it fails, it will continue to the next cases in the conditional group. And only if one of the arguments break beforehand, we use the ifBreak().. another change is instead of using softline for the ifBreak case, just print a hardline instead.

These changes didn't break any existing tests and fix the performance degradation.

var prettier = require("./");
var code = `
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var staticRenderFns = []
render._withStripped = true
`;

prettier.format(code, { parser: "babel", trailingComma: "all" });

The execution time comes down to 0.58s.

> time node test.js
node test.js  0.58s user 0.14s system 89% cpu 0.799 total

Closes #4784

[duailibe]

Even though this didn't break any tests, this is one of the most sensitive parts of our code.

cc @lydell

[lydell]

I'm sorry, I don't understand this piece of code well enough to say whether this is safe. The diff does looks reasonable though, and I think it's worth taking a chance to fix this nasty performance issue.

[j-f1]

Should we have some sort of perf test suite that includes inputs like this one?

[duailibe]

My first reaction is I don’t think so, but I’m not sure