[dsherret]

Draft: the first slice of the line breaking redesign. It uses dprint-core from dprint/dprint#1424 through [patch], so it isn't for merging until that's released.

The newline after = was a possible newline, used when the right side went past the line width. That happened even when the right side would have broken within itself anyway, which it did the next time the file was formatted:

// main, first format
var requireShim =
  (e =>
    typeof require < "u" ? require : typeof Proxy < "u" ? new Proxy(e, {}) : e)(
      function(e) {
        throw Error("Dynamic require of " + e);
      },
    );

// this PR
var requireShim = (e =>
  typeof require < "u" ? require : typeof Proxy < "u" ? new Proxy(e, {}) : e)(
    function(e) {
      throw Error("Dynamic require of " + e);
    },
  );

Now, for variable declarations and assignment expressions, the right side's first line is measured up to where it could break, using fits_on_line_until_first_break. If it doesn't fit after =, the line breaks after =. Otherwise the right side stays on the line, and KeepLineBeforeHere keeps a later line that's too long from breaking before it. Like prettier, some right sides still break after the operator:

• binary and conditional expressions, strings and templates, which break after their operators;
• curried arrow functions, which put each arrow on its own line;
• member expressions that end with a property (ex. options.value, foo(…).bar or x[0] as T), which can only break before that property.

When the line could already break earlier (ex. between declarators), it still does, as before. Text printed without newlines, like a trailing comment, doesn't count towards the width.

Testing

• A new spec for the change and two that must stay the same. The other specs are unchanged.
• The deno repository with its submodules (91,301 files):

	main	This PR
Changes when formatted again, then settles	317	242
Still changing after 20 formats	0	0
Changed output		125 (94 esm.sh bundles, 31 other bundled or minified files, no hand-written files)