Check input and output converters do support the relevant directions

It was previously possible to select an input-only converter for
output or an output-only converter for input. Also add a comment to
explain why failure to probe for the auto output converter isn't an
error, where failure to probe for the auto input converter is.

Pick-to: 6.6 6.5
Task-number: QTBUG-111228
Change-Id: I17dfbbee7d8b5a9629e66d0e1a6a4014b01a7262
Reviewed-by: Ievgenii Meshcheriakov <ievgenii.meshcheriakov@qt.io>

1 files changed, 7 insertions, 4 deletions

diff --git a/examples/corelib/serialization/convert/main.cpp b/examples/corelib/serialization/convert/main.cpp
index 9a2720903b..ddb5a49eed 100644
--- a/examples/corelib/serialization/convert/main.cpp
+++ b/examples/corelib/serialization/convert/main.cpp
@@ -113,8 +113,9 @@ int main(int argc, char *argv[])
             }
         }
 
-        if (!inconv) {
-            fprintf(stderr, "Unknown file format \"%s\"\n", qPrintable(format));
+        if (!inconv || !inconv->directions().testFlag(Converter::Direction::In)) {
+            fprintf(stderr, inconv ? "File format \"%s\" cannot be used for input\n"
+                    : "Unknown input file format \"%s\"\n", qPrintable(format));
             return EXIT_FAILURE;
         }
     }
@@ -129,8 +130,9 @@ int main(int argc, char *argv[])
             }
         }
 
-        if (!outconv) {
-            fprintf(stderr, "Unknown file format \"%s\"\n", qPrintable(format));
+        if (!outconv || !outconv->directions().testFlag(Converter::Direction::Out)) {
+            fprintf(stderr, outconv ? "File format \"%s\" cannot be used for output\n"
+                    : "Unknown output file format \"%s\"\n", qPrintable(format));
             return EXIT_FAILURE;
         }
     }
@@ -184,6 +186,7 @@ int main(int argc, char *argv[])
                 break;
             }
         }
+        // If that failed, loadFile() shall supply a fallback.
     }
 
     // now finally perform the conversion