Created attachment 154875 [details]
test suite

It looks like when the <?oasis-xml-catalog catalog="..."?> PI is used, the catalog it points to is freed too soon to do anything.

Below is my main file, it wants to include another, located in a different directory:

<?xml version="1.0" encoding="UTF-8"?>
<?oasis-xml-catalog catalog="./catalog.xml"?>
<text xmlns:xi="http://www.w3.org/2001/XInclude">
  <xi:include href="header.xml"/>
  <p>some stuff here</p>
</text>

The redirect is supposed to take place via a catalog file with the line:

  <system systemId="header.xml" uri="level1/header.xml"/>

but that does not happen when the PI is used:

$ xmllint --noout --xinclude text.xml
Adding document catalog ./catalog.xml
Free catalog entry ./catalog.xml         <---------- note this
Resolve: sysID header.xml
Failed to parse catalog file:///etc/xml/catalog
Resolve URI header.xml
warning: failed to load external entity "header.xml"
text.xml:4: element include: XInclude error : could not load header.xml, and no fallback was found
Catalogs cleanup
Free catalog entry

But the xmlcatalog has no problem locating the file via the same catalog:

$ xmlcatalog --shell ./catalog.xml
> system header.xml
Resolve sysID header.xml
7012456 Parsing catalog ./catalog.xml
./catalog.xml added to file hash
Found system match header.xml, using level1/header.xml
level1/header.xml
> dump
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
  <system systemId="header.xml" uri="level1/header.xml"/>
</catalog>
> exit
Catalogs cleanup
Free catalog entry header.xml
Free catalog entry ./catalog.xml      <---------- note this
Free catalog entry

For the sake of completeness, here is the nearly-expected output -- except I had to use the default catalog in /etc/xml/ to point to the one in the test suite (via nextCatalog):

$ xmllint --xinclude text.xml
Adding document catalog ./catalog.xml
Free catalog entry ./catalog.xml        <---------- note this, again
Resolve: sysID header.xml
7077992 Parsing catalog file:///etc/xml/catalog
file:///etc/xml/catalog added to file hash
file:///home/Piotr/tmp/libxml2/catalog.xml not found in file hash
7077992 Parsing catalog file:///home/Piotr/tmp/libxml2/catalog.xml
file:///home/Piotr/tmp/libxml2/catalog.xml added to file hash
Found system match header.xml, using file:///home/Piotr/tmp/libxml2/level1/header.xml
<?xml version="1.0" encoding="UTF-8"?>
<?oasis-xml-catalog catalog="./catalog.xml"?>
<text xmlns:xi="http://www.w3.org/2001/XInclude">
  <header xml:base="file:///home/Piotr/tmp/libxml2/level1/header.xml">
   <info>this is the header</info>
</header>
  <p>some stuff here</p>
</text>
Catalogs cleanup
Free catalog entry /home/Piotr/tmp/libxml2/catalog.xml <---------- note this
Free catalog entry file:///etc/xml/catalog
Free catalog entry header.xml
Free catalog entry file:///home/Piotr/tmp/libxml2/catalog.xml
Free catalog entry

---
$ xmllint --version
xmllint: using libxml version 20706
   compiled with: Threads Tree Output Push Reader Patterns Writer SAXv1 FTP HTTP DTDValid HTML Legacy C14N Catalog XPath XPointer XInclude Iconv ISO8859X Unicode Regexps Automata Expr Schemas Schematron Modules Debug Zlib

(running in newly updated Cygwin)
---
Note also bug #167289 (except that there the catalog loads too late), but FWIW let me note that my report is also true of cases when I use --relaxng validation.