梅威瑟：
%%%! LuaLaTeX
\def\doSmth{\the\pagetotal\message{XXXXX::\the\pagetotal::XXXXX}}
\documentclass[a4paper]{article}
\begin{document}
Some text
Some text
Some text
\doSmth
\end{document}
% \bye
此示例中的宏将寄存器\doSmth的值写入\pagetotal页面和日志中。当我使用 LaTeX、纯 TeX 或 luaTeX（后两者经过修改以适应纯 TeX）编译此示例时，页面上和日志中的值都相等，即34.0pt。但是，当使用 luaLaTeX 运行时，页面上的值保持不变，34.0pt但在日志中我得到的是34.22pt。
这种差异似乎很小而且微不足道（而且谁会在乎一些日志呢，对吧？），但它只能说明有些地方出了问题。真正的问题是，在另一个（更复杂得多的）情况下，luaLaTeX 将其视为具有\pagetotal零值（\ifnum \pagetotal > 0因此失败），同时将其值正确打印在页面上（我临时放入了一个宏，就在失败之前\ifnum，与上面的宏相同的命令\doSmth，并在页面上得到了一些，231.8pt在日志中得到了零）。
在 Linux 上使用LuaTeX, Version 1.0.4 (TeX Live 2017) (format=lualatex 2017.9.20)。如有任何帮助，不胜感激。
编辑：经过更多的实验和测试，结果发现问题其实并不严重，或者更准确地说，这里描述的这个不同值的问题和我零值的问题没有关系。我的问题实际上是我自己\dimen0在本地环境中玩得太随意而导致的 bug。
答案1
我没有看出 luatex 和 pdftex 有什么太大区别。
%% https://www.tug.org/utilities/plain/cseq.html
%%
%% everypar: holds tokens added at the beginning of every paragraph.
%%
%% pagetotal: is the accumulated height of the current page.
%%
\loggingall
\tracingpages=1000
\def\doSmth{\immediate\write12{>>before:t=\the\pagetotal .}\the\pagetotal\immediate\write12{>>after:t=\the\pagetotal .}}%
\everypar{\noindent\immediate\write12{>>everypar:t=\the\pagetotal}}%
\def\TESTCHAR{S}%
\def\TESTCHAR{m}%
\def\TESTCHAR{e}%
\def\TESTCHAR{\strut}%
\TESTCHAR%
\par%
\doSmth%
\def\TESTCHAR{S}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{o}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{m}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{e}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{\ }\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{t}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{e}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{x}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{t}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\def\TESTCHAR{\strut}\setbox0\hbox{\TESTCHAR}\immediate\write12{>>\TESTCHAR: wd=\the\wd0, ht=\the\ht0, dp=\the\dp0 .}%
\bye
luatex 与 luatex-plain：
$>mtxrun --script plain test.tex|grep '>>' ;pdftotext test.pdf -;pdffonts test.pdf;
给出
>>before:t=10.0pt.
>>everypar:t=13.5pt
>>after:t=13.5pt.
>>S: wd=5.56pt, ht=7.05pt, dp=0.22pt.
>>o: wd=5.0pt, ht=4.48pt, dp=0.11pt.
>>m: wd=8.33pt, ht=4.42pt, dp=0.0pt.
>>e: wd=4.44pt, ht=4.48pt, dp=0.11pt.
>>\ : wd=3.33pt, ht=0.0pt, dp=0.0pt.
>>t: wd=3.89pt, ht=6.15pt, dp=0.11pt.
>>e: wd=4.44pt, ht=4.48pt, dp=0.11pt.
>>x: wd=5.28pt, ht=4.31pt, dp=0.0pt.
>>t: wd=3.89pt, ht=6.15pt, dp=0.11pt.
>>\relax \unhcopy \strutbox : wd=0.0pt, ht=8.5pt, dp=3.5pt.
10.0pt
1
name type encoding emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
JOCVHR+LMRoman10-Regular CID Type 0C Identity-H yes yes yes 4 0
luatex 带有平原：
$> luatex test.tex|grep '>>';pdftotext test.pdf -;pdffonts test.pdf;
给出
>>everypar:t=0.0pt
>>before:t=10.0pt.
>>everypar:t=13.5pt
>>after:t=13.5pt.
>>S: wd=5.55557pt, ht=6.83331pt, dp=0.0pt.
>>o: wd=5.00002pt, ht=4.30554pt, dp=0.0pt.
>>m: wd=8.33336pt, ht=4.30554pt, dp=0.0pt.
>>e: wd=4.44444pt, ht=4.30554pt, dp=0.0pt.
>>\ : wd=3.33333pt, ht=0.0pt, dp=0.0pt.
>>t: wd=3.8889pt, ht=6.15079pt, dp=0.0pt.
>>e: wd=4.44444pt, ht=4.30554pt, dp=0.0pt.
>>x: wd=5.2778pt, ht=4.30554pt, dp=0.0pt.
>>t: wd=3.8889pt, ht=6.15079pt, dp=0.0pt.
>>\relax \unhcopy \strutbox : wd=0.0pt, ht=8.5pt, dp=3.5pt.
10.0pt
1
name type encoding emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
DLDTEG+CMR10 Type 1 Builtin yes yes no 4 0
和 pdftex
$>pdftex test.tex|grep '>>';pdftotext test.pdf -;pdffonts test.pdf
给出
>>everypar:t=0.0pt
>>before:t=10.0pt.
>>everypar:t=13.5pt
>>after:t=13.5pt.
>>S: wd=5.55557pt, ht=6.83331pt, dp=0.0pt.
>>o: wd=5.00002pt, ht=4.30554pt, dp=0.0pt.
>>m: wd=8.33336pt, ht=4.30554pt, dp=0.0pt.
>>e: wd=4.44444pt, ht=4.30554pt, dp=0.0pt.
>>\ : wd=3.33333pt, ht=0.0pt, dp=0.0pt.
>>t: wd=3.8889pt, ht=6.15079pt, dp=0.0pt.
>>e: wd=4.44444pt, ht=4.30554pt, dp=0.0pt.
>>x: wd=5.2778pt, ht=4.30554pt, dp=0.0pt.
>>t: wd=3.8889pt, ht=6.15079pt, dp=0.0pt.
>>\relax \unhcopy \strutbox : wd=0.0pt, ht=8.5pt, dp=3.5pt.
10.0pt
1
name type encoding emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
DLDTEG+CMR10 Type 1 Builtin yes yes no 4 0
日志中有更多信息，但实际上当我们排版时，会发生一些不同步的事情。当然，这一切都取决于使用的字体：'S'LMRoman10-Regular 的 看起来与'S'CMR10 的 相似，但宽度、高度和深度并不相同 --- 并且深度会影响\pagetotal。在这种情况下，使用\strut会产生相同的结果，因为\strut在 LMRoman10-Regular 和 CMR10 中具有相同的尺寸；但在 LMRoman10-Regular 中'S'和'o'具有不同的深度，而在 CMR10 中，两者的深度都是 0pt。
如果我们看到日志，当 TeX 必须排版 的值时，\pagetotal
其结果之一是 页面构建器使用 的深度'10.0pt'更新，在本例中对于两种字体都是 （是）。这是看到的新值：\pagetotal\strut3.5pt\parskip0.0pt plus 1.0pt\pagetotal\message
\doSmth ->\immediate \write 12{>>before:t=\the \pagetotal .}\the \pagetotal \im
mediate \write 12{>>after:t=\the \pagetotal .}
{vertical mode: \immediate}
\write->>>before:t=\the \pagetotal .
>>before:t=10.0pt.
{\the}
{the character 1}
\everypar->\noindent \immediate \write 12{>>everypar:t=\the \pagetotal }
% t=10.0 g=643.20255 b=10000 p=0 c=100000#
{horizontal mode: \noindent}
{\immediate}
\write->>>everypar:t=\the \pagetotal
>>everypar:t=13.5pt
{the character 1}
{the character 0}
{the character .}
{the character 0}
{the character p}
{the character t}
{\immediate}
\write->>>after:t=\the \pagetotal .
>>after:t=13.5pt.
用 \def\TESTCHAR{S}代替，\def\TESTCHAR{\strut}我们有另一个深度值，在这种情况下，字体不同 0.22pt；并且\def\TESTCHAR{m}两种字体之间以及 pdf 中的值都一致（10pt）。