[NTG-context] Wrong prefix in cross references to formulas in external document

[Yaroslav Beltukov]

Dear Hans and all contributors,

I really appreciate ConTeXt for the right way to obtain high quality
documents. I'm a theoretical physicist and I'm going to write a book. I
think ConTeXt is the right choice to work with a number of formulas,
figures and cross-references. The visual quality of formulas is better than
in regular LaTeX. The new feature with formula autosplitting looks also
very promising. For me it is important to obtain the high quality without a
lot of manual tweaks of each formula for each given document format and
figure placement.

However, I have found a problem with references if I compile one component
only. The references to formulas in other components have wrong prefixes,
e.g. (2.1) instead of (3.1). Needless to say, the right formula references
are very important.

I started looking into this issue. The references to other components are
taken from the whole product as from an external document. It turned out
that this is a general problem with references with prefixes to external
documents. The prefix is stored in a tuc file as a reference to a section
as a sequential number of the header in the document. As a result, the
prefix from the external document is calculated using the structure of the
current document.

Here is the MWE, which consists of two files:
foo.tex:

\defineenumeration[remark][prefix=yes, prefixsegments=chapter:section]

\starttext

Equations: \in[eq1], \in[eq2], \in[eq3], \in[eq4]

Sections: \in[sec1], \in[sec2], \in[sec3], \in[sec4]

Chapters: \in[chap1], \in[chap2], \in[chap3], \in[chap4]

Remarks: \in[remark1], \in[remark2]

\startbodymatter

\chapter[chap1]{Chapter}
\placeformula[eq1]\startformula x = y\stopformula
\chapter[chap2]{Chapter}
\section[sec1]{Section}
\section[sec2]{Section}
\placeformula[eq1]\startformula x = y\stopformula
\placeformula[eq2]\startformula x = y\stopformula

\stopbodymatter

\startappendices

\chapter[chap3]{Chapter}
\section[sec3]{Section}
\placeformula[eq3]\startformula x = y\stopformula
\section[sec4]{Section}
\startremark[remark1]\stopremark
\placeformula[eq4]\startformula x = y\stopformula
\startremark[remark2]\stopremark
\chapter[chap4]{Chapter}

\stopappendices

\stoptext


bar.tex:

\starttext

Equations: \in[foo::eq1], \in[foo::eq2], \in[foo::eq3], \in[foo::eq4]

Sections: \in[foo::sec1], \in[foo::sec2], \in[foo::sec3], \in[foo::sec4]

Chapters: \in[foo::chap1], \in[foo::chap2], \in[foo::chap3], \in[foo::chap4]

Remarks: \in[foo::remark1], \in[foo::remark2]

% any chapters and sections here

\stoptext

It is expected to have the same first page on these documents:

Equations: 1.1, 2.2, A.1, A.2
Sections: 2.1, 2.2, A.1, A.2
Chapters: 1, 2, A, B
Remarks: A.2.1, A.2.2

However, the bar.tex produces wrong prefixes to formulas and remarks. The
output depends on the document structure of bar.tex, not foo.tex.

I started looking into the source code. Thanks to lua, it is not a big deal
to track the problem. The prefixdata is complemented by the sectiondata
after the loading the tuc file. So, the question is: is it possible to
store the full prefixdata with all necessary prefix numbers in the tuc
file? Here is my proposal to change the source code:

--- strc-lst-old.lmt    2023-01-29 11:30:15.610309948 +0300
+++ strc-lst.lmt        2023-01-29 12:10:08.864228923 +0300
@@ -266,6 +266,16 @@
     if r and not r.section then
         r.section = structures.sections.currentid()
     end
+    -- store sectiondata in prefixdata (necessary for external files)
+    if t.prefixdata and r.section then
+        local sectiondata = structures.sections.collected[r.section]
+        if sectiondata then
+            for k, v in next, sectiondata do
+                t.prefixdata[k] = v
+            end
+        end
+    end
+    --
     local b = r and t.block
     if r and not b then
         local s = r.section

--- strc-ref-old.lmt    2023-01-29 11:30:15.823643904 +0300
+++ strc-ref.lmt        2023-01-29 12:07:45.697109862 +0300
@@ -2318,7 +2318,17 @@
     if data then
         numberdata = lists.reordered(data) -- data.numberdata
         if numberdata then
-            helpers.prefix(data,prefixspec)
+            -- helpers.prefix(data,prefixspec)
+            -- use the actual numbers from prefixdata
+            local prefixdata = data.prefixdata
+            if prefixdata then
+                -- adapted from helpers.prefix (not sure)
+                if (prefixspec and prefixspec == no) or prefixdata.prefix
== no then
+                    prefixdata = false
+                end
+                sections.typesetnumber(prefixdata,"prefix", prefixspec or
false, prefixdata)
+            end
+            --

 sections.typesetnumber(numberdata,"number",numberspec,numberdata)
         else
             local useddata = data.useddata

After this small change, all the references are correct. However, I'm quite
new to ConTeXt, so maybe here are some caveats. It would be great to fix
the references to formulas, especially for the forthcoming document about
maths.

Best regards,
Yaroslav Beltukov
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