Enforce QTextDocument::MarkdownFeature compatibility at compile time

We use md4c for parsing markdown.  It provides flags to control the
feature set that will be supported when parsing particular documents.
QTextMarkdownImporter::Feature is a fine-grained set of flags that
exactly match the md4c feature flags that we support in Qt so far.
QTextMarkdownImporter is a private exported class (new in 5.14).
We don't expect the corresponding flags in md4c to change in
incompatible ways in the future: the md4c authors have as much respect
for avoiding compatibility issues as we do, and likely will only add
features, not remove them.

We now enforce QTextMarkdownImporter::Features compatibility with
QTextDocument::MarkdownFeatures by setting them directly.  We check
QTextMarkdownImporter::Features compatibility with md4c's #define'd
feature flags using static asserts, so that any hypothetical
incompatibility would be detected at compile time.
The enum conversion from QTextDocument::MarkdownFeatures to
QTextMarkdownImporter::Features is moved to a new QTextMarkdownImporter
constructor; thus the conversions from QTextDocument::MarkdownFeatures
to QTextMarkdownImporter::Features, and then to unsigned (in
QTextMarkdownImporter::import()) are adjacent in the same private class
implementation.  If incompatibility ever occurred, we would need to
replace one or both of those with another suitable conversion function.

Change-Id: I0bf8a21eb7559df1d38406b948ef657f9060c67b
Reviewed-by: Vitaly Fanaskov <vitaly.fanaskov@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/gui/text/qtextdocument.cpp b/src/gui/text/qtextdocument.cpp
index 22c249d604..e94f635651 100644
--- a/src/gui/text/qtextdocument.cpp
+++ b/src/gui/text/qtextdocument.cpp
@@ -3420,7 +3420,7 @@ QString QTextDocument::toMarkdown(QTextDocument::MarkdownFeatures features) cons
 #if QT_CONFIG(textmarkdownreader)
 void QTextDocument::setMarkdown(const QString &markdown, QTextDocument::MarkdownFeatures features)
 {
-    QTextMarkdownImporter(static_cast<QTextMarkdownImporter::Features>(int(features))).import(this, markdown);
+    QTextMarkdownImporter(features).import(this, markdown);
 }
 #endif