`credential fill` subcommand incorrectly assumes required field(s)

[Adolar0042]

Current behavior 😯

gix credential fill fails if url field is not provided, even if protocol and host are set

url

When this special attribute is read by git credential, the value is parsed as a URL and treated as if its constituent parts were read (e.g., url=https://example.com would behave as if protocol=https and host=example.com had been provided).

from the git-credential documentation

Expected behavior 🤔

gix credential fill should only fail if both url aswell as protocol and host are not set

Git behavior

git credential fill only fails if both url aswell as protocol and host are not set

Steps to reproduce 🕹

1. Run

$ gix credential fill << EOF
protocol=https
host=github.com
EOF

2. Run

$ git credential fill << EOF
protocol=https
host=github.com
EOF

3. Compare output (git works, gix fails due to missing url field)

[Byron]

Thanks a lot for reporting!

I took a quick look and think this patch could be a start:

diff --git a/gix-credentials/src/program/main.rs b/gix-credentials/src/program/main.rs
index 34f4163a01..9f9ee0dccb 100644
--- a/gix-credentials/src/program/main.rs
+++ b/gix-credentials/src/program/main.rs
@@ -55,8 +55,6 @@ pub enum Error {
     Context(#[from] crate::protocol::context::decode::Error),
     #[error("Credentials for {url:?} could not be obtained")]
     CredentialsMissing { url: BString },
-    #[error("The url wasn't provided in input - the git credentials protocol mandates this")]
-    UrlMissing,
 }
 
 pub(crate) mod function {
@@ -89,14 +87,13 @@ pub(crate) mod function {
         let mut buf = Vec::<u8>::with_capacity(512);
         stdin.read_to_end(&mut buf)?;
         let ctx = Context::from_bytes(&buf)?;
-        if ctx.url.is_none() {
-            return Err(Error::UrlMissing);
-        }
         let res = credentials(action, ctx).map_err(|err| Error::Helper { source: Box::new(err) })?;
         match (action, res) {
             (Action::Get, None) => {
                 return Err(Error::CredentialsMissing {
-                    url: Context::from_bytes(&buf)?.url.expect("present and checked above"),
+                    url: Context::from_bytes(&buf)?
+                        .url
+                        .expect("present as it would fail to parse without"),
                 })
             }
             (Action::Get, Some(ctx)) => ctx.write_to(stdout)?,
diff --git a/gix-credentials/src/protocol/context/serde.rs b/gix-credentials/src/protocol/context/serde.rs
index a4c91b9637..21d7465fbc 100644
--- a/gix-credentials/src/protocol/context/serde.rs
+++ b/gix-credentials/src/protocol/context/serde.rs
@@ -85,6 +85,8 @@ pub mod decode {
         Encoding(#[from] context::Error),
         #[error("Invalid format in line {line:?}, expecting key=value")]
         Syntax { line: BString },
+        #[error("The url wasn't provided in input - neither directly nor via 'host' and 'protocol' fields")]
+        UrlMissing,
     }
 
     impl Context {
@@ -141,6 +143,9 @@ pub mod decode {
                     _ => {}
                 }
             }
+            if url.is_none() {
+                todo!()
+            }
             Ok(ctx)
         }
     }

It would allow the credential helper program to continue and assume that Context can only be created if it's valid.
This also means that if there is no URL, it now has to build it from all available parts. This is laborious but can be tested well.