From 56135f3ff3c2bd8c5a403e26f779cfd488ec3d33 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@gmail.com>
Date: Fri, 18 Aug 2023 14:29:37 -0500
Subject: [PATCH] fix(builder): UnknownValueParser shouldn't error on flag
 absense

Fixes #5079
---
 clap_builder/src/builder/value_parser.rs | 67 +++++++++++++++---------
 tests/builder/error.rs                   |  2 +-
 2 files changed, 43 insertions(+), 26 deletions(-)

diff --git a/clap_builder/src/builder/value_parser.rs b/clap_builder/src/builder/value_parser.rs
index 38fbb57f..1f0ef925 100644
--- a/clap_builder/src/builder/value_parser.rs
+++ b/clap_builder/src/builder/value_parser.rs
@@ -2228,32 +2228,49 @@ impl TypedValueParser for UnknownArgumentValueParser {
         &self,
         cmd: &crate::Command,
         arg: Option<&crate::Arg>,
-        _value: &std::ffi::OsStr,
+        value: &std::ffi::OsStr,
     ) -> Result<Self::Value, crate::Error> {
-        let arg = match arg {
-            Some(arg) => arg.to_string(),
-            None => "..".to_owned(),
-        };
-        let err = crate::Error::unknown_argument(
-            cmd,
-            arg,
-            self.arg.as_ref().map(|s| (s.as_str().to_owned(), None)),
-            false,
-            crate::output::Usage::new(cmd).create_usage_with_title(&[]),
-        );
-        #[cfg(feature = "error-context")]
-        let err = {
-            debug_assert_eq!(
-                err.get(crate::error::ContextKind::Suggested),
-                None,
-                "Assuming `Error::unknown_argument` doesn't apply any `Suggested` so we can without caution"
-            );
-            err.insert_context_unchecked(
-                crate::error::ContextKind::Suggested,
-                crate::error::ContextValue::StyledStrs(self.suggestions.clone()),
-            )
-        };
-        Err(err)
+        TypedValueParser::parse_ref_(self, cmd, arg, value, ValueSource::CommandLine)
+    }
+
+    fn parse_ref_(
+        &self,
+        cmd: &crate::Command,
+        arg: Option<&crate::Arg>,
+        _value: &std::ffi::OsStr,
+        source: ValueSource,
+    ) -> Result<Self::Value, crate::Error> {
+        match source {
+            ValueSource::DefaultValue => {
+                TypedValueParser::parse_ref_(&StringValueParser::new(), cmd, arg, _value, source)
+            }
+            ValueSource::EnvVariable | ValueSource::CommandLine => {
+                let arg = match arg {
+                    Some(arg) => arg.to_string(),
+                    None => "..".to_owned(),
+                };
+                let err = crate::Error::unknown_argument(
+                    cmd,
+                    arg,
+                    self.arg.as_ref().map(|s| (s.as_str().to_owned(), None)),
+                    false,
+                    crate::output::Usage::new(cmd).create_usage_with_title(&[]),
+                );
+                #[cfg(feature = "error-context")]
+                let err = {
+                    debug_assert_eq!(
+                        err.get(crate::error::ContextKind::Suggested),
+                        None,
+                        "Assuming `Error::unknown_argument` doesn't apply any `Suggested` so we can without caution"
+                    );
+                    err.insert_context_unchecked(
+                        crate::error::ContextKind::Suggested,
+                        crate::error::ContextValue::StyledStrs(self.suggestions.clone()),
+                    )
+                };
+                Err(err)
+            }
+        }
     }
 }
 
diff --git a/tests/builder/error.rs b/tests/builder/error.rs
index bd94c6bd..833a614d 100644
--- a/tests/builder/error.rs
+++ b/tests/builder/error.rs
@@ -263,7 +263,7 @@ fn unknown_argument_flag() {
     ]);
 
     let res = cmd.clone().try_get_matches_from(["test"]);
-    assert!(res.is_err());
+    assert!(res.is_ok());
 
     let res = cmd.try_get_matches_from(["test", "--ignored"]);
     assert!(res.is_err());