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Format: spurious space at end of line #7720

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vicuna opened this issue Feb 2, 2018 · 4 comments

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commented Feb 2, 2018

Original bug ID: 7720
Reporter: gmelquiond
Assigned to: @Octachron
Status: assigned (set by @Octachron on 2018-02-04T17:24:44Z)
Resolution: open
Priority: normal
Severity: minor
Version: 4.06.0
Category: standard library
Has duplicate: #7804

Bug description

The code

Format.set_margin 10; Format.printf "@[@[123456@ @[A@]@ B@]@]@\n";;

produces

123456=
A B

where = denotes a spurious space.

I am also wondering why A was not put at the end of the first line. (Removing the box around A does so. Removing one of the outer boxes does so too. Removing B does so too.) I guess the two issues are related.

@vicuna

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commented Feb 2, 2018

Comment author: @Octachron

The space at the end of the line is not spurious from the point of view of Format's implementation.

This is due to the fact that "Format.set_margin 10" also sets the maximum indentation limit to 5. Consequently, the second box is rejected to the left with a forced new line. Since the break is introduced by the opening of the box, the previous break hint "@ " is printed as a space.

The easiest fix in this situation is to also adjust the maximum indentation limit:

Format.set_margin 10; Format.set_max_indent 8;
Format.printf "@[@[123456@ @[A@]@ B@]@]@\n";;

displays the expected output

123456·A
B

Similarly, the difference in behavior that you observed by shortening the length of the format string is due to the fact that when the content of a box fits on a line, all formatting indication (and the maximum indentation limit) are ignored because the box is replaced by a fits box.

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commented Feb 2, 2018

Comment author: gmelquiond

There is something I am missing. The documentation of set_max_indent says: "once this limit is reached, new pretty-printing boxes are rejected to the left, if they do not fit on the current line." But the box containing A does fit on the line. So why would it be rejected to the left?

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commented Feb 2, 2018

Comment author: @Octachron

You are right, there is a mismatch between the documentation and the implementation here: the rejection to the left happens if the parent box does not fit on the line, i.e.

"once this limit is reached, new pretty-printing boxes are rejected to the left, if their parent box do not fit on the current line."

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commented Feb 3, 2018

Comment author: @Octachron

I have proposed a documentation fix at #1596.
Do you wish to be mentionned as a reporter, and if yes under which name?

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