Set correct path to (biblatex) bibliography databases that are entered relative to child documents.

Fixes: #11105

src/Buffer.cpp

@@ -3150,9 +3150,28 @@ vector<docstring> const Buffer::prepareBibFilePaths(OutputParams const & runpara
 		string utf8input = to_utf8(bit.first);
 		string database =
 			prepareFileNameForLaTeX(utf8input, ".bib", runparams.nice);
-		FileName const try_in_file =
+		FileName try_in_file =
 			makeAbsPath(database + ".bib", filePath());
-		bool const not_from_texmf = try_in_file.isReadableFile();
+		bool not_from_texmf = try_in_file.isReadableFile();
+		// If the file has not been found, try with the real file name
+		// (it might come from a child in a sub-directory)
+		if (!not_from_texmf) {
+			try_in_file = bit.second;
+			if (try_in_file.isReadableFile()) {
+				// Check if the file is in texmf
+				FileName kpsefile(findtexfile(changeExtension(utf8input, "bib"), "bib", true));
+				not_from_texmf = kpsefile.empty()
+						|| kpsefile.absFileName() != try_in_file.absFileName();
+				if (not_from_texmf)
+					// If this exists, make path relative to the master
+					// FIXME Unicode
+					database =
+						removeExtension(prepareFileNameForLaTeX(
+											to_utf8(makeRelPath(from_utf8(try_in_file.absFileName()),
+																from_utf8(filePath()))),
+											".bib", runparams.nice));
+			}
+		}
 
 		if (!runparams.inComment && !runparams.dryrun && !runparams.nice &&
 		    not_from_texmf) {

src/support/filetools.cpp

@@ -1124,7 +1124,8 @@ cmd_ret const runCommand(string const & cmd)
 }
 
 
-FileName const findtexfile(string const & fil, string const & /*format*/)
+FileName const findtexfile(string const & fil, string const & /*format*/,
+						   bool const onlykpse)
 {
 	/* There is no problem to extend this function too use other
 	   methods to look for files. It could be setup to look
@@ -1137,9 +1138,11 @@ FileName const findtexfile(string const & fil, string const & /*format*/)
 
 	// If the file can be found directly, we just return a
 	// absolute path version of it.
-	FileName const absfile(makeAbsPath(fil));
-	if (absfile.exists())
-		return absfile;
+	if (!onlykpse) {
+		FileName const absfile(makeAbsPath(fil));
+		if (absfile.exists())
+			return absfile;
+	}
 
 	// Now we try to find it using kpsewhich.
 	// It seems from the kpsewhich manual page that it is safe to use

src/support/filetools.h

@@ -305,7 +305,8 @@ bool readLink(FileName const & file, FileName & link);
  * \param format The file format as used by kpsewhich, e.g. "bib", "bst" etc.
  */
 FileName const findtexfile(std::string const & fil,
-			      std::string const & format);
+						   std::string const & format,
+						   bool const onlykpse = false);
 
 /** \param file1, file2 the two files to be compared. Must have absolute paths.
  *  \returns 1 if \c file1 has a more recent timestamp than \c file2,