From 1a427d559320d3246b06ec61c6b5bb1daee87b12 Mon Sep 17 00:00:00 2001
From: Charlie Tonneslan <cst0520@gmail.com>
Date: Sun, 17 May 2026 08:58:55 -0400
Subject: [PATCH] emit secondary tag handles (e.g. !!str) on Node::SetTag
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When a node's tag started with "!!" — the YAML secondary tag handle,
as in "!!str" or "!!int" — EmitFromEvents stripped a single '!' and
emitted the rest as a LocalTag. The remaining string ("!str") then
failed the LocalTag character regex on the inner '!' and the emitter
bailed out with INVALID_TAG, truncating output after "!".

Reproduction from #1373:

    YAML::Node root;
    YAML::Node s{"hello"};
    s.SetTag("!!str");
    root["some_string"] = s;
    root["some_int"] = 2;
    std::cout << root;  // -> "some_string: !"

Recognize the "!!" prefix in EmitProps and route it through
SecondaryTag with the rest of the tag content. After this:

    some_string: !!str hello
    some_int: 2

Added two regression tests under NodeTest covering both the secondary
("!!") and primary ("!") handle paths.

Closes #1373.

Signed-off-by: Charlie Tonneslan <cst0520@gmail.com>
---
 src/emitfromevents.cpp              |  7 ++++++-
 test/integration/load_node_test.cpp | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/emitfromevents.cpp b/src/emitfromevents.cpp
index 350bde648..0d410c426 100644
--- a/src/emitfromevents.cpp
+++ b/src/emitfromevents.cpp
@@ -117,7 +117,12 @@ void EmitFromEvents::BeginNode() {
 
 void EmitFromEvents::EmitProps(const std::string& tag, anchor_t anchor) {
   if (!tag.empty() && tag != "?" && tag != "!"){
-      if (tag[0] == '!') {
+      if (tag.size() >= 2 && tag[0] == '!' && tag[1] == '!') {
+        // Tags like "!!str" use the secondary tag handle; emit them through
+        // SecondaryTag so the rendered output keeps both bangs instead of
+        // failing the LocalTag regex check on the inner '!'. See #1373.
+        m_emitter << SecondaryTag(std::string(tag.begin()+2, tag.end()));
+      } else if (tag[0] == '!') {
         m_emitter << LocalTag(std::string(tag.begin()+1, tag.end()));
       } else {
         m_emitter << VerbatimTag(tag);
diff --git a/test/integration/load_node_test.cpp b/test/integration/load_node_test.cpp
index d7698434c..65366175e 100644
--- a/test/integration/load_node_test.cpp
+++ b/test/integration/load_node_test.cpp
@@ -231,6 +231,33 @@ TEST(NodeTest, EmitEmptyNode) {
   EXPECT_EQ("", std::string(emitter.c_str()));
 }
 
+// Regression for #1373: emitting a node whose tag begins with "!!"
+// (a YAML secondary tag handle, e.g. "!!str") used to bail out with
+// INVALID_TAG and truncate the output after the first '!'.
+TEST(NodeTest, EmitSetTagSecondaryHandle) {
+  Node root;
+  Node string_node{"hello"};
+  string_node.SetTag("!!str");
+  root["some_string"] = string_node;
+  root["some_int"] = 2;
+
+  Emitter emitter;
+  emitter << root;
+  EXPECT_EQ("some_string: !!str hello\nsome_int: 2",
+            std::string(emitter.c_str()));
+}
+
+TEST(NodeTest, EmitSetTagPrimaryHandle) {
+  Node root;
+  Node string_node{"hello"};
+  string_node.SetTag("!mytag");
+  root["v"] = string_node;
+
+  Emitter emitter;
+  emitter << root;
+  EXPECT_EQ("v: !mytag hello", std::string(emitter.c_str()));
+}
+
 TEST(NodeTest, ParseNodeStyle) {
   EXPECT_EQ(EmitterStyle::Flow, Load("[1, 2, 3]").Style());
   EXPECT_EQ(EmitterStyle::Flow, Load("{foo: bar}").Style());