Stop dropping notes on the floor

Fixes #15 (which has been open for years) by ensuring the margin piece count is properly reset to zero on every page.

Many thanks to casackett for providing a minimal repro, and to UlrikBuchholtz for pointing me in the right direction for the fix (and pointing out a few typos).

Makefile

@@ -10,9 +10,9 @@ marginfix.sty:marginfix.dtx marginfix.ins
 marginfix.pdf:marginfix.dtx
 	pdflatex marginfix.dtx
 
-.PHONY: test
+.PHONY: test clean
 
-test:margintest.pdf tufte.pdf ragged.pdf defer.pdf phantom.pdf float.pdf stretch.pdf
+test:margintest.pdf tufte.pdf ragged.pdf defer.pdf phantom.pdf float.pdf stretch.pdf issue-15.pdf
 
 margintest.pdf:marginfix.sty test/margintest.tex
 	pdflatex test/margintest.tex
@@ -34,3 +34,9 @@ float.pdf:marginfix.sty test/float.tex
 
 stretch.pdf:marginfix.sty test/stretch.tex
 	pdflatex test/stretch.tex
+
+issue-15.pdf:marginfix.sty test/issue-15.tex
+	pdflatex test/issue-15.tex
+
+clean:
+	rm *.log *.aux *.pdf tufte.out marginfix.sty

marginfix.dtx

@@ -12,10 +12,10 @@
 %
 %<package>\NeedsTeXFormat{LaTeX2e}
 %<package>\ProvidesPackage{marginfix}%
-           [2013/09/08 v1.1 Fix Margin Paragraphs]
+           [2020/05/06 v1.2 Fix Margin Paragraphs]
 %<*driver>
 \documentclass{ltxdoc}
-\CheckSum{1158}
+\CheckSum{1159}
 %\OnlyDescription % (un)comment this line to show (hide) source code
 \RecordChanges
 \EnableCrossrefs
@@ -70,6 +70,9 @@
 %       {(SDH) Globally calculate margin phantoms over 4 passes.}
 % \changes{v1.1}{2013/09/08}
 %       {(SDH) Add \cs{topskip} to notes at the top of the margin.}
+% \changes{v1.2}{2020/05/06}
+%       {(SDH) Fix long-standing bug where margin notes called out in
+%        the last few points of a page were being entirely dropped.}
 %
 % \GetFileInfo{marginfix.dtx}
 % \title{\Lopt{marginfix} package documentation}
@@ -512,7 +515,7 @@
 % In passing we'll define the cons macro, which fully-expands
 % its second argument, but makes sure to only expand the first
 % one once, so that any fragile control sequences in it are
-% corectly protected.  We also define snoc, which prepends.
+% correctly protected.  We also define snoc, which prepends.
 % Note that we could put the \cs{temp@} definition into a group
 % if it was really gonna matter\ldots
 %    \begin{macrocode}
@@ -691,7 +694,7 @@
 % line up the notes with their callouts).  This procedure happens in
 % four passes.  But first, we initialize \cs{Mfx@marginheight} to
 % \cs{@colroom}, which is the height of the page minus any floats that
-% have been added to the top of bottom (these floats may extend into the
+% have been added to the top or bottom (these floats may extend into the
 % margins: in the future we may look into detecting this and using the
 % whole page, with overwide floats blocked off as phantoms).  We add
 % \cs{@colroom} rather than assigning it because any global or per-page
@@ -784,7 +787,7 @@
 % We now define the various |\MFX@margin@...@down| macros.
 % At this stage in the game, the only difference between  notes
 % and skips is that we ignore skips before any notes by setting
-% \cs{mfx@build@note} initially to \cs{@gobble}.  Once we've
+% \cs{mfx@build@skip} initially to \cs{@gobble}.  Once we've
 % seen the first note, skips are treated exactly the same: as
 % fixed-height material.  If there is room in the current piece
 % for the given height, then we prepend it to \cs{mfx@marginout},
@@ -928,8 +931,8 @@
 % \end{macros}
 %
 % \begin{macros}{\MFX@leftmargin}
-% And here is the logic to figure out which margin were in, based
-% on the page number and other flags.  This is another conditional-like
+% And here is the logic to figure out which margin we're in, based on
+% the page number and other flags.  This is another conditional-like
 % macro, and should be used after an \cs{if}, as in
 % \cs{if}\cs{MFX@leftmargin}\ldots\cs{else}\ldots\cs{fi}.
 %
@@ -1039,7 +1042,7 @@
 % look for a piece that can fit this note, making sure to decrement
 % the piece count and pop off a phantom for each new piece we check.
 % Once it's found, we add the note back to \cs{mfx@marginout} with
-% the corect piece.
+% the correct piece.
 %    \begin{macrocode}
   \if\MFX@check@fit{\advance\Mfx@piece@count\m@ne
                     \MFX@popdimen\dimen@\mfx@phantomheights}{\ht#1+\dp#1}%
@@ -1111,7 +1114,7 @@
   \let\@elt\MFX@buildmargin@piece
   \MFX@run@clear\mfx@marginpieces
   \let\@elt\relax
-  \Mfx@piece@count\z@
+  \global\Mfx@piece@count\z@
 }
 %    \end{macrocode}
 % \end{macros}

test/issue-15.tex

@@ -0,0 +1,15 @@
+\documentclass{tufte-book}
+\usepackage{marginfix}
+\geometry{paperheight=10in,paperwidth=8in,textheight=8in,left=0.6in}
+
+\begin{document}
+\chapter{Test}
+\newpage
+%\vspace*{34547299sp} % same
+\vspace*{34547300sp} % [
+%\vspace*{34744565sp} % ]
+%\vspace*{34744566sp} % break
+\[ x \]
+% Make sure that the note actually appears anywhere!
+Lorem ipsum dolor sit amet \marginnote{Ut vero duis quaeque mea}
+\end{document}