The algorithm used for breaking a paragraph in LaTeX export is changed
for avoiding spurious blank lines causing too much vertical space.
This change is tied to the introduction of a new inset (with two
different specializations) helping in either outputing LaTeX paragraph
breaks or separating environments in LyX. Both of the above goals were
previously achieved by the ---Separator--- layout and can now be
accomplished by the new inset in a more natural way. As an example,
after leaving an environment by hitting the Return key for two times,
a third return automatically inserts a parbreak inset, which is
equivalent to the old separator layout, i.e., it also introduces a
blank line in the output. If this blank line is not wanted, the
parbreak separator can be changed to a plain separator by a right
click of the mouse. Of course, an environment can still be separated
by the following one by using the Alt+P+Return shortcut (or the
corresponding menu key), but now the plain separator inset is used
instead of the old separator layout, such that no blank line occurs in
the LaTeX output.
Old documents are converted such that the LaTeX output remains unchanged.
As a result of this conversion, the old separator layout is replaced by
the new parbreak inset, which may also appear in places where the old
algorithm was introducing blank lines while the new one is not.
Note that not all blank lines were actually affecting the LaTeX output,
because a blank line is simply ignored by the TeX engine when it occurs
in the so called "vertical mode" (e.g., after an alignment environment).
The old ---Separator--- layout is now gone and old layout files using it
are also automatically converted.
Round trip conversions between old and new format should leave a document
unchanged. This means that the new behavior about paragraph breaking is
not "carried back" to the old format. Indeed, this would need introducing
special LaTeX commands in ERT that would accumulate in roundtrip
conversions, horribly cluttering the document. So, when converting a
modified document to old formats, the LaTeX output may slightly differ in
vertical spacing if the document is processed by an old version of LyX.
In other words, forward compatibility is guaranteed, but not backwards.
This has the advantage of simplifying our code and to produce the
correct output: the small capitals should have the exact same width as
the lower case letters.
The slanted fonts are also translated to oblique on Qt side, but this
does not seems to have an effect in my testing. It may be that proper
oblique fonts need to be installed.
lyx2lyx sets all new math packages to off when converting from old formats.
This is correct if any command which would cause an automatic package loading
exists in the document. However, it is wrong if no command exists: This leads
to problems if later a command is added (bug #9069), which is especially
annoying for templates.
The fix consists of two parts:
1) convert_use_package() considers now the used commands like
revert_use_package(), and uses them to decide whether to set the package to
auto or off.
2) convert_undertilde() and revert_undertilde() use a slightly adjusted copy of
convert_use_package() and revert_use_package(), so that the bug is also
fixed for undertilde. We cannot use the latter functions directly, because
of "\usepackage undertilde" vs. "\use_undertilde".
When doing the lyx2lyx round trip of the 2.0.8 user guide from format
413 -> 474 -> 413 you get an invalid document, because the math packages
mhchem and undertilde are incorrectly converted.
It turned out that the old reversion code did only work for particular
package oderings. The new one works for abitrary sorted packages.
When doing the lyx2lyx round trip of the 2.0.8 user guide from format
413 -> 474 -> 413 you do not get a zero diff. The most important problem is
caused by the conversion of the argument insets to the old syntax: This
conversion adds an additional empty line (harmless), and it destroys the
document structure if the first inset in e.g. a subsection is not an argument
inset, but e.g. an index or label inset.
The fix is quite easy: Ensure that the paragraph begin is set to the first
argument inset.
revert_justification() issues a warning if the \justification parameter does
not exist, and LyX itself always writes it unconditionally as well, so add it
also in lyx2lyx when converting old documents.
Currently this does not have any user visible effect, but it decouples the
default value of BufferParams::justification from the conversion of old
documents: Now it is possible to set the default to false in LyX, and old
documents will still be converted correctly.
In C++98 std::istream does not use an operator bool(), but an operator
void*() instead, which prevents some unwanted conversions (this is one
possible implementation of the safe bool idiom).
In C++11 std::istream uses explicit operator bool, which prevents the unwanted
conversions using a new language feature.
This change does not have any effect on correct code, but prevents some
mistakes.
