From b8af0d8fa2f169c7d3a470bd83af3f57b60e344b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20Sch=C3=A4fer?= <jonas@zombofant.net>
Date: Fri, 20 Dec 2024 08:57:46 +0100
Subject: [PATCH] xmpp_parsers: `--features disable-validation`

It was broken in multiple ways:

- xso did not honour it: unknown children and attributes would cause a
  parse error even with `--features disable-validation` set on parsers.
  For this, we introduce a new feature flag on xso, `non-pedantic`,
  which defaults unknown children and attributes to discard instead of
  fail.

  Note that individual XSOs can still choose to be always pedantic or
  always lenient by explicitly declaring the intent via the
  `on_unknown_child` and `on_unknown_attribute` metas.

- Many tests in `xmpp_parsers` were broken with `--features
  disable-validation`. They now all pass while *still* being rn with
  `disable-validation` set: In that case, they test that parsing in fact
  succeeds.
---
 parsers/Cargo.toml                 |  2 +-
 parsers/src/bind.rs                |  1 +
 parsers/src/blocking.rs            |  1 +
 parsers/src/bob.rs                 |  1 +
 parsers/src/data_forms_validate.rs |  8 +++++---
 parsers/src/delay.rs               |  1 +
 parsers/src/disco.rs               |  1 +
 parsers/src/ecaps2.rs              |  1 +
 parsers/src/eme.rs                 |  1 +
 parsers/src/forwarding.rs          |  3 ++-
 parsers/src/hashes.rs              |  1 +
 parsers/src/idle.rs                |  1 +
 parsers/src/jingle.rs              | 19 +++++++++----------
 parsers/src/jingle_ft.rs           | 26 +++++++++++++++++++++++---
 parsers/src/media_element.rs       |  1 +
 parsers/src/message_correct.rs     |  1 +
 parsers/src/muc/muc.rs             |  1 +
 parsers/src/muc/user.rs            |  2 ++
 parsers/src/occupant_id.rs         |  1 +
 parsers/src/roster.rs              |  9 ++++++++-
 parsers/src/sasl.rs                |  2 +-
 parsers/src/stanza_id.rs           |  1 +
 parsers/src/util/macro_tests.rs    | 24 ++++++++++++++++++++++++
 xso/Cargo.toml                     |  1 +
 xso/src/lib.rs                     | 18 ++++++++++++++----
 25 files changed, 104 insertions(+), 24 deletions(-)

diff --git a/parsers/Cargo.toml b/parsers/Cargo.toml
index 6f233c39..3b070eb3 100644
--- a/parsers/Cargo.toml
+++ b/parsers/Cargo.toml
@@ -32,7 +32,7 @@ uuid = { version = "1.9.1", features = ["v4"] }
 # Build xmpp-parsers to make components instead of clients.
 component = []
 # Disable validation of unknown attributes.
-disable-validation = []
+disable-validation = [ "xso/non-pedantic" ]
 # Enable serde support in jid crate
 serde = [ "jid/serde" ]
 # Enable some additional logging in helpers
diff --git a/parsers/src/bind.rs b/parsers/src/bind.rs
index d8486692..4ea5e4fa 100644
--- a/parsers/src/bind.rs
+++ b/parsers/src/bind.rs
@@ -77,6 +77,7 @@ impl From<BindResponse> for Jid {
 mod tests {
     use super::*;
     use minidom::Element;
+    #[cfg(not(feature = "disable-validation"))]
     use xso::error::{Error, FromElementError};
 
     #[cfg(target_pointer_width = "32")]
diff --git a/parsers/src/blocking.rs b/parsers/src/blocking.rs
index d41fe11c..897f8657 100644
--- a/parsers/src/blocking.rs
+++ b/parsers/src/blocking.rs
@@ -62,6 +62,7 @@ pub struct Blocked;
 
 #[cfg(test)]
 mod tests {
+    #[cfg(not(feature = "disable-validation"))]
     use xso::error::{Error, FromElementError};
 
     use super::*;
diff --git a/parsers/src/bob.rs b/parsers/src/bob.rs
index 1f09c8ec..40cbd3df 100644
--- a/parsers/src/bob.rs
+++ b/parsers/src/bob.rs
@@ -194,6 +194,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn unknown_child() {
         let elem: Element = "<data xmlns='urn:xmpp:bob' cid='sha1+8f35fef110ffc5df08d579a50083ff9308fb6242@bob.xmpp.org'><coucou/></data>"
             .parse()
diff --git a/parsers/src/data_forms_validate.rs b/parsers/src/data_forms_validate.rs
index 37365931..57d8ce21 100644
--- a/parsers/src/data_forms_validate.rs
+++ b/parsers/src/data_forms_validate.rs
@@ -448,7 +448,11 @@ mod tests {
     }
 
     #[test]
-    fn test_fails_with_invalid_children() -> Result<(), Error> {
+    #[cfg_attr(
+        feature = "disable-validation",
+        should_panic = "Validate::try_from(element).is_err()"
+    )]
+    fn test_fails_with_invalid_children() {
         let cases = [
             r#"<validate xmlns='http://jabber.org/protocol/xdata-validate'><basic /><open /></validate>"#,
             r#"<validate xmlns='http://jabber.org/protocol/xdata-validate'><unknown /></validate>"#,
@@ -460,7 +464,5 @@ mod tests {
                 .expect(&format!("Failed to parse {}", case));
             assert!(Validate::try_from(element).is_err());
         }
-
-        Ok(())
     }
 }
diff --git a/parsers/src/delay.rs b/parsers/src/delay.rs
index 717115c2..c103fe5f 100644
--- a/parsers/src/delay.rs
+++ b/parsers/src/delay.rs
@@ -81,6 +81,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<delay xmlns='urn:xmpp:delay' stamp='2002-09-10T23:08:25+00:00'><coucou/></delay>"
diff --git a/parsers/src/disco.rs b/parsers/src/disco.rs
index 8428bd43..1cf51063 100644
--- a/parsers/src/disco.rs
+++ b/parsers/src/disco.rs
@@ -258,6 +258,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid() {
         let elem: Element =
             "<query xmlns='http://jabber.org/protocol/disco#info'><coucou/></query>"
diff --git a/parsers/src/ecaps2.rs b/parsers/src/ecaps2.rs
index e31dc3cf..04f4c099 100644
--- a/parsers/src/ecaps2.rs
+++ b/parsers/src/ecaps2.rs
@@ -219,6 +219,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element = "<c xmlns='urn:xmpp:caps'><hash xmlns='urn:xmpp:hashes:2' algo='sha-256'>K1Njy3HZBThlo4moOD5gBGhn0U0oK7/CbfLlIUDi6o4=</hash><hash xmlns='urn:xmpp:hashes:1' algo='sha3-256'>+sDTQqBmX6iG/X3zjt06fjZMBBqL/723knFIyRf0sg8=</hash></c>".parse().unwrap();
         let error = ECaps2::try_from(elem).unwrap_err();
diff --git a/parsers/src/eme.rs b/parsers/src/eme.rs
index fafba2b4..ca75d0d0 100644
--- a/parsers/src/eme.rs
+++ b/parsers/src/eme.rs
@@ -72,6 +72,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<encryption xmlns='urn:xmpp:eme:0' namespace='urn:xmpp:otr:0'><coucou/></encryption>"
diff --git a/parsers/src/forwarding.rs b/parsers/src/forwarding.rs
index 4963b2a7..2584fc80 100644
--- a/parsers/src/forwarding.rs
+++ b/parsers/src/forwarding.rs
@@ -56,8 +56,9 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
-        let elem: Element = "<forwarded xmlns='urn:xmpp:forward:0'><coucou/></forwarded>"
+        let elem: Element = "<forwarded xmlns='urn:xmpp:forward:0'><message xmlns='jabber:client'/><coucou/></forwarded>"
             .parse()
             .unwrap();
         let error = Forwarded::try_from(elem).unwrap_err();
diff --git a/parsers/src/hashes.rs b/parsers/src/hashes.rs
index 332e69af..0febefc0 100644
--- a/parsers/src/hashes.rs
+++ b/parsers/src/hashes.rs
@@ -305,6 +305,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element = "<hash xmlns='urn:xmpp:hashes:2' algo='sha-1'><coucou/></hash>"
             .parse()
diff --git a/parsers/src/idle.rs b/parsers/src/idle.rs
index 08b14ef8..54cb235d 100644
--- a/parsers/src/idle.rs
+++ b/parsers/src/idle.rs
@@ -42,6 +42,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<idle xmlns='urn:xmpp:idle:1' since='2017-05-21T20:19:55+01:00'><coucou/></idle>"
diff --git a/parsers/src/jingle.rs b/parsers/src/jingle.rs
index 9f14da0a..f216d6d2 100644
--- a/parsers/src/jingle.rs
+++ b/parsers/src/jingle.rs
@@ -754,7 +754,7 @@ mod tests {
     }
 
     #[test]
-    fn test_invalid_reason() {
+    fn test_missing_reason_text() {
         let elem: Element = "<jingle xmlns='urn:xmpp:jingle:1' action='session-initiate' sid='coucou'><reason/></jingle>".parse().unwrap();
         let error = Jingle::try_from(elem).unwrap_err();
         let message = match error {
@@ -765,23 +765,22 @@ mod tests {
             message,
             "Missing child field 'reason' in ReasonElement element."
         );
+    }
 
-        let elem: Element = "<jingle xmlns='urn:xmpp:jingle:1' action='session-initiate' sid='coucou'><reason><a/></reason></jingle>".parse().unwrap();
-        let error = Jingle::try_from(elem).unwrap_err();
-        let message = match error {
-            FromElementError::Invalid(Error::Other(string)) => string,
-            _ => panic!(),
-        };
-        assert_eq!(message, "Unknown child in ReasonElement element.");
-
-        let elem: Element = "<jingle xmlns='urn:xmpp:jingle:1' action='session-initiate' sid='coucou'><reason><a xmlns='http://www.w3.org/1999/xhtml'/></reason></jingle>".parse().unwrap();
+    #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
+    fn test_invalid_child_in_reason() {
+        let elem: Element = "<jingle xmlns='urn:xmpp:jingle:1' action='session-initiate' sid='coucou'><reason><decline/><a/></reason></jingle>".parse().unwrap();
         let error = Jingle::try_from(elem).unwrap_err();
         let message = match error {
             FromElementError::Invalid(Error::Other(string)) => string,
             _ => panic!(),
         };
         assert_eq!(message, "Unknown child in ReasonElement element.");
+    }
 
+    #[test]
+    fn test_multiple_reason_children() {
         let elem: Element = "<jingle xmlns='urn:xmpp:jingle:1' action='session-initiate' sid='coucou'><reason><decline/></reason><reason/></jingle>".parse().unwrap();
         let error = Jingle::try_from(elem).unwrap_err();
         let message = match error {
diff --git a/parsers/src/jingle_ft.rs b/parsers/src/jingle_ft.rs
index 746581cc..23b9d155 100644
--- a/parsers/src/jingle_ft.rs
+++ b/parsers/src/jingle_ft.rs
@@ -304,7 +304,7 @@ mod tests {
     }
 
     #[test]
-    fn test_received() {
+    fn test_received_valid() {
         let elem: Element = "<received xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='initiator'/>".parse().unwrap();
         let received = Received::try_from(elem).unwrap();
         assert_eq!(received.name, ContentId(String::from("coucou")));
@@ -313,7 +313,11 @@ mod tests {
         let received2 = Received::try_from(elem2).unwrap();
         assert_eq!(received2.name, ContentId(String::from("coucou")));
         assert_eq!(received2.creator, Creator::Initiator);
+    }
 
+    #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
+    fn test_received_unknown_child() {
         let elem: Element = "<received xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='initiator'><coucou/></received>".parse().unwrap();
         let error = Received::try_from(elem).unwrap_err();
         let message = match error {
@@ -321,7 +325,10 @@ mod tests {
             _ => panic!(),
         };
         assert_eq!(message, "Unknown child in Received element.");
+    }
 
+    #[test]
+    fn test_received_missing_name() {
         let elem: Element =
             "<received xmlns='urn:xmpp:jingle:apps:file-transfer:5' creator='initiator'/>"
                 .parse()
@@ -335,7 +342,10 @@ mod tests {
             message,
             "Required attribute field 'name' on Received element missing."
         );
+    }
 
+    #[test]
+    fn test_received_invalid_creator() {
         let elem: Element = "<received xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='coucou'/>".parse().unwrap();
         let error = Received::try_from(elem).unwrap_err();
         let message = match error {
@@ -361,7 +371,7 @@ mod tests {
     }
 
     #[test]
-    fn test_checksum() {
+    fn test_checksum_valid() {
         let elem: Element = "<checksum xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='initiator'><file><hash xmlns='urn:xmpp:hashes:2' algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash></file></checksum>".parse().unwrap();
         let hash = vec![
             195, 73, 156, 39, 41, 115, 10, 127, 128, 126, 251, 134, 118, 169, 45, 203, 111, 138,
@@ -388,15 +398,22 @@ mod tests {
                 hash: hash.clone()
             })
         );
+    }
 
-        let elem: Element = "<checksum xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='initiator'><coucou/></checksum>".parse().unwrap();
+    #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
+    fn test_checksum_unknown_child() {
+        let elem: Element = "<checksum xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='initiator'><file><hash xmlns='urn:xmpp:hashes:2' algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash></file><coucou/></checksum>".parse().unwrap();
         let error = Checksum::try_from(elem).unwrap_err();
         let message = match error {
             FromElementError::Invalid(Error::Other(string)) => string,
             other => panic!("unexpected error: {:?}", other),
         };
         assert_eq!(message, "Unknown child in Checksum element.");
+    }
 
+    #[test]
+    fn test_checksum_missing_name() {
         let elem: Element = "<checksum xmlns='urn:xmpp:jingle:apps:file-transfer:5' creator='initiator'><file><hash xmlns='urn:xmpp:hashes:2' algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash></file></checksum>".parse().unwrap();
         let error = Checksum::try_from(elem).unwrap_err();
         let message = match error {
@@ -407,7 +424,10 @@ mod tests {
             message,
             "Required attribute field 'name' on Checksum element missing."
         );
+    }
 
+    #[test]
+    fn test_checksum_invalid_creator() {
         let elem: Element = "<checksum xmlns='urn:xmpp:jingle:apps:file-transfer:5' name='coucou' creator='coucou'><file><hash xmlns='urn:xmpp:hashes:2' algo='sha-1'>w0mcJylzCn+AfvuGdqkty2+KP48=</hash></file></checksum>".parse().unwrap();
         let error = Checksum::try_from(elem).unwrap_err();
         let message = match error {
diff --git a/parsers/src/media_element.rs b/parsers/src/media_element.rs
index 44c617ec..d17b0da1 100644
--- a/parsers/src/media_element.rs
+++ b/parsers/src/media_element.rs
@@ -154,6 +154,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_unknown_child() {
         let elem: Element = "<media xmlns='urn:xmpp:media-element'><coucou/></media>"
             .parse()
diff --git a/parsers/src/message_correct.rs b/parsers/src/message_correct.rs
index 9b3c2c94..200a00a8 100644
--- a/parsers/src/message_correct.rs
+++ b/parsers/src/message_correct.rs
@@ -62,6 +62,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<replace xmlns='urn:xmpp:message-correct:0' id='coucou'><coucou/></replace>"
diff --git a/parsers/src/muc/muc.rs b/parsers/src/muc/muc.rs
index c9aa0b08..61398037 100644
--- a/parsers/src/muc/muc.rs
+++ b/parsers/src/muc/muc.rs
@@ -113,6 +113,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_muc_invalid_child() {
         let elem: Element = "<x xmlns='http://jabber.org/protocol/muc'><coucou/></x>"
             .parse()
diff --git a/parsers/src/muc/user.rs b/parsers/src/muc/user.rs
index 50cba625..9835de87 100644
--- a/parsers/src/muc/user.rs
+++ b/parsers/src/muc/user.rs
@@ -317,6 +317,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element = "<x xmlns='http://jabber.org/protocol/muc#user'>
                 <coucou/>
@@ -490,6 +491,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_continue_invalid() {
         let elem: Element =
             "<continue xmlns='http://jabber.org/protocol/muc#user'><foobar/></continue>"
diff --git a/parsers/src/occupant_id.rs b/parsers/src/occupant_id.rs
index a175f647..040fbf96 100644
--- a/parsers/src/occupant_id.rs
+++ b/parsers/src/occupant_id.rs
@@ -53,6 +53,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<occupant-id xmlns='urn:xmpp:occupant-id:0' id='foo'><coucou/></occupant-id>"
diff --git a/parsers/src/roster.rs b/parsers/src/roster.rs
index 67226423..6e044bb8 100644
--- a/parsers/src/roster.rs
+++ b/parsers/src/roster.rs
@@ -289,7 +289,7 @@ mod tests {
     }
 
     #[test]
-    fn test_invalid_item() {
+    fn test_item_missing_jid() {
         let elem: Element = "<query xmlns='jabber:iq:roster'><item/></query>"
             .parse()
             .unwrap();
@@ -302,7 +302,10 @@ mod tests {
             message,
             "Required attribute field 'jid' on Item element missing."
         );
+    }
 
+    #[test]
+    fn test_item_invalid_jid() {
         let elem: Element = "<query xmlns='jabber:iq:roster'><item jid=''/></query>"
             .parse()
             .unwrap();
@@ -311,7 +314,11 @@ mod tests {
             format!("{error}"),
             "text parse error: no domain found in this JID"
         );
+    }
 
+    #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
+    fn test_item_unknown_child() {
         let elem: Element =
             "<query xmlns='jabber:iq:roster'><item jid='coucou'><coucou/></item></query>"
                 .parse()
diff --git a/parsers/src/sasl.rs b/parsers/src/sasl.rs
index de4abb1b..b18c8343 100644
--- a/parsers/src/sasl.rs
+++ b/parsers/src/sasl.rs
@@ -157,7 +157,7 @@ pub struct Failure {
 
     /// A human-readable explanation for the failure.
     #[xml(extract(n = .., name = "text", fields(
-        attribute(type_ = String, name = "xml:lang"),
+        attribute(type_ = String, name = "xml:lang", default),
         text(type_ = String),
     )))]
     pub texts: BTreeMap<Lang, String>,
diff --git a/parsers/src/stanza_id.rs b/parsers/src/stanza_id.rs
index 04575d3d..ae65cc84 100644
--- a/parsers/src/stanza_id.rs
+++ b/parsers/src/stanza_id.rs
@@ -76,6 +76,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "disable-validation", should_panic = "Result::unwrap_err")]
     fn test_invalid_child() {
         let elem: Element =
             "<stanza-id xmlns='urn:xmpp:sid:0' by='a@b' id='x'><coucou/></stanza-id>"
diff --git a/parsers/src/util/macro_tests.rs b/parsers/src/util/macro_tests.rs
index 0da7e6d2..c08c5919 100644
--- a/parsers/src/util/macro_tests.rs
+++ b/parsers/src/util/macro_tests.rs
@@ -121,6 +121,10 @@ fn empty_namespace_mismatch() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn empty_unexpected_attribute() {
     #[allow(unused_imports)]
     use core::{
@@ -136,6 +140,10 @@ fn empty_unexpected_attribute() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn empty_unexpected_child() {
     #[allow(unused_imports)]
     use core::{
@@ -869,6 +877,10 @@ fn text_extract_negative_absent_child() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn text_extract_negative_unexpected_attribute_in_child() {
     #[allow(unused_imports)]
     use core::{
@@ -886,6 +898,10 @@ fn text_extract_negative_unexpected_attribute_in_child() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn text_extract_negative_unexpected_child_in_child() {
     #[allow(unused_imports)]
     use core::{
@@ -1807,6 +1823,10 @@ fn ignore_unknown_attributes_positive() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn ignore_unknown_attributes_negative_unexpected_child() {
     #[allow(unused_imports)]
     use core::{
@@ -1849,6 +1869,10 @@ fn ignore_unknown_children_positive() {
 }
 
 #[test]
+#[cfg_attr(
+    feature = "disable-validation",
+    should_panic = "unexpected result: Ok("
+)]
 fn ignore_unknown_children_negative_unexpected_attribute() {
     #[allow(unused_imports)]
     use core::{
diff --git a/xso/Cargo.toml b/xso/Cargo.toml
index 7096307e..4a0e5f36 100644
--- a/xso/Cargo.toml
+++ b/xso/Cargo.toml
@@ -29,6 +29,7 @@ default = [ "std" ]
 macros = [ "dep:xso_proc", "rxml/macros" ]
 minidom = [ "xso_proc/minidom"]
 panicking-into-impl = ["xso_proc/panicking-into-impl"]
+non-pedantic = []
 std = []
 
 [package.metadata.docs.rs]
diff --git a/xso/src/lib.rs b/xso/src/lib.rs
index 568e1cd1..3417936e 100644
--- a/xso/src/lib.rs
+++ b/xso/src/lib.rs
@@ -324,13 +324,18 @@ impl<T: AsXmlText> AsOptionalXmlText for Option<T> {
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
 pub enum UnknownAttributePolicy {
     /// All unknown attributes are discarded.
+    ///
+    /// This is the default policy if the crate is built with the
+    /// `non-pedantic` feature.
+    #[cfg_attr(feature = "non-pedantic", default)]
     Discard,
 
     /// The first unknown attribute which is encountered generates a fatal
     /// parsing error.
     ///
-    /// This is the default policy.
-    #[default]
+    /// This is the default policy if the crate is built **without** the
+    /// `non-pedantic` feature.
+    #[cfg_attr(not(feature = "non-pedantic"), default)]
     Fail,
 }
 
@@ -356,13 +361,18 @@ impl UnknownAttributePolicy {
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
 pub enum UnknownChildPolicy {
     /// All unknown children are discarded.
+    ///
+    /// This is the default policy if the crate is built with the
+    /// `non-pedantic` feature.
+    #[cfg_attr(feature = "non-pedantic", default)]
     Discard,
 
     /// The first unknown child which is encountered generates a fatal
     /// parsing error.
     ///
-    /// This is the default policy.
-    #[default]
+    /// This is the default policy if the crate is built **without** the
+    /// `non-pedantic` feature.
+    #[cfg_attr(not(feature = "non-pedantic"), default)]
     Fail,
 }