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The go/printer (and thus gofmt) uses a heuristic to determine whether to break alignment between elements of an expression list which is spread across multiple lines. The heuristic only kicked in if the entry sizes (character length) was above a certain threshold (20) and the ratio between the previous and current entry size was above a certain value (4). This heuristic worked reasonably most of the time, but also led to unfortunate breaks in many cases where a single entry was suddenly much smaller (or larger) then the previous one. The behavior of gofmt was sufficiently mysterious in some of these situations that many issues were filed against it. The simplest solution to address this problem is to remove the heuristic altogether and have a programmer introduce empty lines to force different alignments if it improves readability. The problem with that approach is that the places where it really matters, very long tables with many (hundreds, or more) entries, may be machine-generated and not "post-processed" by a human (e.g., unicode/utf8/tables.go). If a single one of those entries is overlong, the result would be that the alignment would force all comments or values in key:value pairs to be adjusted to that overlong value, making the table hard to read (e.g., that entry may not even be visible on screen and all other entries seem spaced out too wide). Instead, we opted for a slightly improved heuristic that behaves much better for "normal", human-written code. 1) The threshold is increased from 20 to 40. This disables the heuristic for many common cases yet even if the alignment is not "ideal", 40 is not that many characters per line with todays screens, making it very likely that the entire line remains "visible" in an editor. 2) Changed the heuristic to not simply look at the size ratio between current and previous line, but instead considering the geometric mean of the sizes of the previous (aligned) lines. This emphasizes the "overall picture" of the previous lines, rather than a single one (which might be an outlier). 3) Changed the ratio from 4 to 2.5. Now that we ignore sizes below 40, a ratio of 4 would mean that a new entry would have to be 4 times bigger (160) or smaller (10) before alignment would be broken. A ratio of 2.5 seems more sensible. Applied updated gofmt to all of src and misc. Also tested against several former issues that complained about this and verified that the output for the given examples is satisfactory (added respective test cases). Some of the files changed because they were not gofmt-ed in the first place. For #644. For #7335. For #10392. (and probably more related issues) Fixes #22852. Change-Id: I5e48b3d3b157a5cf2d649833b7297b33f43a6f6e |
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