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, 21 insertions, 0 deletions

diff --git a/src/gui/text/qtextmarkdownimporter.cpp b/src/gui/text/qtextmarkdownimporter.cpp
index fe7e422923..87ade1f973 100644
--- a/src/gui/text/qtextmarkdownimporter.cpp
+++ b/src/gui/text/qtextmarkdownimporter.cpp
@@ -60,6 +60,22 @@ static const QChar Space = QLatin1Char(' ');
 // TODO maybe eliminate the margins after all views recognize BlockQuoteLevel, CSS can format it, etc.
 static const int BlockQuoteIndent = 40; // pixels, same as in QTextHtmlParserNode::initializeProperties
 
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureCollapseWhitespace) == MD_FLAG_COLLAPSEWHITESPACE);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeaturePermissiveATXHeaders) == MD_FLAG_PERMISSIVEATXHEADERS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeaturePermissiveURLAutoLinks) == MD_FLAG_PERMISSIVEURLAUTOLINKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeaturePermissiveMailAutoLinks) == MD_FLAG_PERMISSIVEEMAILAUTOLINKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureNoIndentedCodeBlocks) == MD_FLAG_NOINDENTEDCODEBLOCKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureNoHTMLBlocks) == MD_FLAG_NOHTMLBLOCKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureNoHTMLSpans) == MD_FLAG_NOHTMLSPANS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureTables) == MD_FLAG_TABLES);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureStrikeThrough) == MD_FLAG_STRIKETHROUGH);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeaturePermissiveWWWAutoLinks) == MD_FLAG_PERMISSIVEWWWAUTOLINKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeaturePermissiveAutoLinks) == MD_FLAG_PERMISSIVEAUTOLINKS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureTasklists) == MD_FLAG_TASKLISTS);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::FeatureNoHTML) == MD_FLAG_NOHTML);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::DialectCommonMark) == MD_DIALECT_COMMONMARK);
+Q_STATIC_ASSERT(int(QTextMarkdownImporter::DialectGitHub) == MD_DIALECT_GITHUB);
+
 // --------------------------------------------------------
 // MD4C callback function wrappers
 
@@ -122,6 +138,11 @@ QTextMarkdownImporter::QTextMarkdownImporter(QTextMarkdownImporter::Features fea
 {
 }
 
+QTextMarkdownImporter::QTextMarkdownImporter(QTextDocument::MarkdownFeatures features)
+  : QTextMarkdownImporter(static_cast<QTextMarkdownImporter::Features>(int(features)))
+{
+}
+
 void QTextMarkdownImporter::import(QTextDocument *doc, const QString &markdown)
 {
     MD_PARSER callbacks = {