fix: add postinst template conditions (microsoft#225097)

Author: rzhao271

resources/linux/debian/postinst.template

@@ -31,6 +31,7 @@ if [ "@@NAME@@" != "code-oss" ]; then
 	# Register apt repository
 	eval $(apt-config shell APT_SOURCE_PARTS Dir::Etc::sourceparts/d)
 	CODE_SOURCE_PART=${APT_SOURCE_PARTS}vscode.list
+	CODE_SOURCE_PART_DEB822=${APT_SOURCE_PARTS}vscode.sources
 
 	eval $(apt-config shell APT_TRUSTED_PARTS Dir::Etc::trustedparts/d)
 	CODE_TRUSTED_PART=${APT_TRUSTED_PARTS}microsoft.gpg
@@ -41,19 +42,22 @@ if [ "@@NAME@@" != "code-oss" ]; then
 		db_get @@NAME@@/add-microsoft-repo || true
 	fi
 
-	# Install repository source list
+	# Determine whether to install the repository source list
 	WRITE_SOURCE=0
 	if [ "$RET" = false ]; then
-		# The user does not want to add the microsoft repository
+		# The user does not want to add the Microsoft repository
 		WRITE_SOURCE=0
-	elif grep -q "http://packages.microsoft.com/repos/vscode" $CODE_SOURCE_PART; then
+	elif [ -f "$CODE_SOURCE_PART_DEB822" ]; then
+		# The user has migrated themselves to the DEB822 format
+		WRITE_SOURCE=0
+	elif [ -f "$CODE_SOURCE_PART" ] && (grep -q "http://packages.microsoft.com/repos/vscode" $CODE_SOURCE_PART); then
 		# Migrate from old repository
 		WRITE_SOURCE=2
-	elif grep -q "http://packages.microsoft.com/repos/code" $CODE_SOURCE_PART; then
+	elif [ -f "$CODE_SOURCE_PART" ] && (grep -q "http://packages.microsoft.com/repos/code" $CODE_SOURCE_PART); then
 		# Migrate from old repository
 		WRITE_SOURCE=2
 	elif apt-cache policy | grep -q "https://packages.microsoft.com/repos/code"; then
-		# Skip following checks if the repo is already known to apt
+		# The user is already on the new repository
 		WRITE_SOURCE=0
 	elif [ ! -f $CODE_SOURCE_PART ] && [ ! -f /etc/rpi-issue ]; then
 		# Write source list if it does not exist and we're not running on Raspberry Pi OS