From 921a20722cab989cfc4df02826b42e379709c4e6 Mon Sep 17 00:00:00 2001
From: David Malcolm <dmalcolm@redhat.com>
Date: Wed, 11 Feb 2026 17:14:17 -0500
Subject: [PATCH] diagnostics: add disclosure widgets to HTML output [PR116792]

Examples:
  https://dmalcolm.fedorapeople.org/gcc/2026-02-11/bad-fndef-1.C.html
  https://dmalcolm.fedorapeople.org/gcc/2026-02-11/nested-diagnostics-1.C.html
  https://dmalcolm.fedorapeople.org/gcc/2026-02-11/malloc-ipa-8-double-free.c.html

TODO: blurb

TODO: Maybe we want to add a boolean hint when pushing nesting levels
about whether the child diagnostics should be shown by default???

gcc/ChangeLog:
	PR diagnostics/116792
	* diagnostics/html-sink.cc (HTML_STYLE): Add styling for
	<summary>.
	(html_builder::push_nesting_level): For nesting levels not
	at the top-level, add a
	"<details><summary>Details</summary><details>" to get a disclosure
	widget.  Open the top two levels of disclosure widget by
	default.
	(html_builder::make_element_for_diagnostic): Add details and
	summary to execution path, to get a disclosure widget.  This
	hides the execution path until expanded.
---
 gcc/diagnostics/html-sink.cc | 63 +++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 12 deletions(-)

diff --git a/gcc/diagnostics/html-sink.cc b/gcc/diagnostics/html-sink.cc
index 33cbb8c2413..6f3721ff776 100644
--- a/gcc/diagnostics/html-sink.cc
+++ b/gcc/diagnostics/html-sink.cc
@@ -331,6 +331,9 @@ static const char * const HTML_STYLE
      "                   font-weight: bold; }\n"
      "    .gcc-quoted-text { font-weight: bold;\n"
      "                       font-family: mono; }\n"
+     "    summary { display: list-item;\n"
+     "              color: #0088ce; }\n"
+     "    summary:hover { text-decoration: underline; }\n"
      "  </style>\n");
 
 /* A little JavaScript for ease of navigation.
@@ -602,17 +605,49 @@ void
 html_builder::push_nesting_level ()
 {
   gcc_assert (m_cur_diagnostic_element);
-  auto new_nesting_level = std::make_unique<xml::element> ("ul", false);
-  add_nesting_level_attr (*new_nesting_level,
-			  m_cur_nesting_levels.size () + 1);
-  xml::element *current_nesting_level = nullptr;
-  if (!m_cur_nesting_levels.empty ())
-    current_nesting_level = m_cur_nesting_levels.back ();
-  m_cur_nesting_levels.push_back (new_nesting_level.get ());
-  if (current_nesting_level)
-    current_nesting_level->add_child (std::move (new_nesting_level));
+
+  if (m_cur_nesting_levels.empty ())
+    {
+      /* At the top level, add a <ul> to hold elements, with
+	 no <details> or <summary>.  */
+      auto new_ul = std::make_unique<xml::element> ("ul", false);
+      add_nesting_level_attr (*new_ul,
+			      m_cur_nesting_levels.size () + 1);
+      m_cur_nesting_levels.push_back (new_ul.get ());
+      m_cur_diagnostic_element->add_child (std::move (new_ul));
+    }
   else
-    m_cur_diagnostic_element->add_child (std::move (new_nesting_level));
+    {
+      /* Within nested levels, add
+	 <details><summary>Details</summary><ul/></details>
+	 to the current nesting level, and push the nesting level
+	 so that child elements appear within the <ul>. */
+
+      xml::element *current_nesting_level = m_cur_nesting_levels.back ();
+
+      auto details = std::make_unique<xml::element> ("details", false);
+      add_nesting_level_attr (*details,
+			      m_cur_nesting_levels.size () + 1);
+
+      /* Open the top two levels by default.  */
+      if (m_cur_nesting_levels.size () < 3)
+	details->set_attr ("open", "true");
+
+      {
+	auto summary = std::make_unique<xml::element> ("summary", false);
+	summary->add_text ("Details");
+	details->add_child (std::move (summary));
+      }
+      {
+	auto new_ul = std::make_unique<xml::element> ("ul", false);
+	add_nesting_level_attr (*new_ul,
+				m_cur_nesting_levels.size () + 1);
+	m_cur_nesting_levels.push_back (new_ul.get ());
+	details->add_child (std::move (new_ul));
+      }
+
+      current_nesting_level->add_child (std::move (details));
+    }
 }
 
 void
@@ -1146,7 +1181,9 @@ html_builder::make_element_for_diagnostic (const diagnostic_info &diagnostic,
       xp.push_tag ("div");
       xp.set_attr ("id", "execution-path");
 
-      xp.push_tag ("label", true);
+      xp.push_tag ("details");
+
+      xp.push_tag ("summary", true);
       const int num_events = path->num_events ();
       pretty_printer pp;
       pp_printf_n (&pp, num_events,
@@ -1154,7 +1191,7 @@ html_builder::make_element_for_diagnostic (const diagnostic_info &diagnostic,
 		   "Execution path with %i events",
 		   num_events);
       xp.add_text_from_pp (pp);
-      xp.pop_tag ("label");
+      xp.pop_tag ("summary");
 
       std::string event_id_prefix (diag_id + "-event-");
       html_path_label_writer event_label_writer (xp, *this, *path,
@@ -1164,6 +1201,8 @@ html_builder::make_element_for_diagnostic (const diagnostic_info &diagnostic,
       print_path_as_html (xp, *path, m_context, &event_label_writer,
 			  dspp);
 
+      xp.pop_tag ("details");
+
       xp.pop_tag ("div");
     }
 
-- 
2.49.0