[LyX/2.4.1-devel] Disable language package choice if the class preloads a package

[Juergen Spitzmueller]

commit d29baf59a4a69ad022bca7ee63b3512838b295a2
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Apr 13 10:07:18 2024 +0200

    Disable language package choice if the class preloads a package
    
    (cherry picked from commit 5477451e36cd9ff4e99aefea2627fbf63e028004)
---
 src/frontends/qt/GuiDocument.cpp | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt/GuiDocument.cpp b/src/frontends/qt/GuiDocument.cpp
index d4471cff7b..e020ab92c2 100644
--- a/src/frontends/qt/GuiDocument.cpp
+++ b/src/frontends/qt/GuiDocument.cpp
@@ -4217,15 +4217,30 @@ void GuiDocument::paramsToDialog()
 
 	// LaTeX input encoding: set after the fonts (see below)
 
-	int p = langModule->languagePackageCO->findData(toqstr(bp_.lang_package));
+	// If the class provides babel or polyglossia, do not allow
+	// to change that
+	bool const extern_babel =
+		documentClass().provides("babel");
+	bool const extern_polyglossia =
+		documentClass().provides("polyglossia");
+
+	int p = -1;
+	if (extern_babel)
+		p = langModule->languagePackageCO->findData(toqstr("babel"));
+	else if (extern_polyglossia)
+		p = langModule->languagePackageCO->findData(toqstr("polyglossia"));
+	else
+		p = langModule->languagePackageCO->findData(toqstr(bp_.lang_package));
+
 	if (p == -1) {
 		langModule->languagePackageCO->setCurrentIndex(
-			  langModule->languagePackageCO->findData("custom"));
+			langModule->languagePackageCO->findData("custom"));
 		langModule->languagePackageLE->setText(toqstr(bp_.lang_package));
 	} else {
 		langModule->languagePackageCO->setCurrentIndex(p);
 		langModule->languagePackageLE->clear();
 	}
+	langModule->languagePackageCO->setEnabled(!extern_babel && !extern_polyglossia);
 
 	//color
 	if (bp_.isfontcolor) {