1 files changed, 92 insertions, 0 deletions
diff --git a/src/markdownrenderer.cpp b/src/markdownrenderer.cpp
new file mode 100644
index 0000000..a9b8177
--- /dev/null
+++ b/src/markdownrenderer.cpp
@@ -0,0 +1,92 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+// cmark-gfm's headers are C and carry no Qt interaction, so the gmime
+// include-order rule does not apply here. They still go first, for consistency
+// with mimeparser.cpp.
+#include <cmark-gfm.h>
+#include <cmark-gfm-core-extensions.h>
+
+#include "markdownrenderer.h"
+
+#include <QByteArray>
+
+#include <cstdlib>
+
+namespace {
+
+/// The extensions this application enables, by cmark-gfm's own names.
+///
+/// `table` is absent deliberately, not by oversight: tables render badly
+/// across mail clients regardless of who generates them. `tagfilter` is absent
+/// because CMARK_OPT_SAFE already suppresses raw HTML wholesale, which is the
+/// stronger measure.
+const char *const kExtensions[] = { "autolink", "strikethrough", "tasklist" };
+
+}  // namespace
+
+QString MarkdownRenderer::toHtml(const QString &markdown)
+{
+    if (markdown.isEmpty())
+        return {};
+
+    // Idempotent and required before cmark_find_syntax_extension() can resolve
+    // any name. Calling it per render rather than once at startup keeps this
+    // function free of initialisation order concerns; it is a hash lookup
+    // after the first call.
+    cmark_gfm_core_extensions_ensure_registered();
+
+    // SAFE suppresses raw HTML in the INPUT. It does not escape the output,
+    // which is markup by definition.
+    const int options = CMARK_OPT_DEFAULT | CMARK_OPT_SAFE;
+
+    cmark_parser *parser = cmark_parser_new(options);
+    if (!parser)
+        return {};
+
+    for (const char *name : kExtensions) {
+        // A missing extension is a broken installation rather than a
+        // condition to handle: the library was found by CMake. Skipping it
+        // degrades to plain CommonMark rather than crashing.
+        if (cmark_syntax_extension *extension = cmark_find_syntax_extension(name))
+            cmark_parser_attach_syntax_extension(parser, extension);
+    }
+
+    const QByteArray utf8 = markdown.toUtf8();
+    cmark_parser_feed(parser, utf8.constData(), static_cast<size_t>(utf8.size()));
+
+    cmark_node *document = cmark_parser_finish(parser);
+    if (!document) {
+        cmark_parser_free(parser);
+        return {};
+    }
+
+    // The extension list must be passed to the renderer as well as to the
+    // parser. Passing nullptr here parses the tasklist correctly and then
+    // renders it as a plain list item, which looks like the extension never
+    // worked.
+    char *html = cmark_render_html(document, options,
+                                   cmark_parser_get_syntax_extensions(parser));
+    const QString result = html ? QString::fromUtf8(html) : QString();
+
+    free(html);
+    cmark_node_free(document);
+    cmark_parser_free(parser);
+
+    return result;
+}