Convert PluginFailedToLoad to named fields (#11124)

# Description

Part of #10700

# User-Facing Changes

None

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

N/A

crates/nu-plugin/src/plugin/declaration.rs

@@ -136,9 +136,9 @@ impl Command for PluginDeclaration {
             let stdout_reader = match &mut child.stdout {
                 Some(out) => out,
                 None => {
-                    return Err(ShellError::PluginFailedToLoad(
-                        "Plugin missing stdout reader".into(),
-                    ))
+                    return Err(ShellError::PluginFailedToLoad {
+                        msg: "Plugin missing stdout reader".into(),
+                    })
                 }
             };
             get_plugin_encoding(stdout_reader)?

crates/nu-plugin/src/plugin/mod.rs

@@ -146,17 +146,21 @@ pub fn get_signature(
             }
         };
 
-        ShellError::PluginFailedToLoad(error_msg)
+        ShellError::PluginFailedToLoad { msg: error_msg }
     })?;
 
     let mut stdin_writer = child
         .stdin
         .take()
-        .ok_or_else(|| ShellError::PluginFailedToLoad("plugin missing stdin writer".into()))?;
+        .ok_or_else(|| ShellError::PluginFailedToLoad {
+            msg: "plugin missing stdin writer".into(),
+        })?;
     let mut stdout_reader = child
         .stdout
         .take()
-        .ok_or_else(|| ShellError::PluginFailedToLoad("Plugin missing stdout reader".into()))?;
+        .ok_or_else(|| ShellError::PluginFailedToLoad {
+            msg: "Plugin missing stdout reader".into(),
+        })?;
     let encoding = get_plugin_encoding(&mut stdout_reader)?;
 
     // Create message to plugin to indicate that signature is required and
@@ -177,14 +181,16 @@ pub fn get_signature(
     let signatures = match response {
         PluginResponse::Signature(sign) => Ok(sign),
         PluginResponse::Error(err) => Err(err.into()),
-        _ => Err(ShellError::PluginFailedToLoad(
-            "Plugin missing signature".into(),
-        )),
+        _ => Err(ShellError::PluginFailedToLoad {
+            msg: "Plugin missing signature".into(),
+        }),
     }?;
 
     match child.wait() {
         Ok(_) => Ok(signatures),
-        Err(err) => Err(ShellError::PluginFailedToLoad(format!("{err}"))),
+        Err(err) => Err(ShellError::PluginFailedToLoad {
+            msg: format!("{err}"),
+        }),
     }
 }
 
@@ -438,19 +444,23 @@ fn print_help(plugin: &mut impl Plugin, encoder: impl PluginEncoder) {
 
 pub fn get_plugin_encoding(child_stdout: &mut ChildStdout) -> Result<EncodingType, ShellError> {
     let mut length_buf = [0u8; 1];
-    child_stdout.read_exact(&mut length_buf).map_err(|e| {
-        ShellError::PluginFailedToLoad(format!("unable to get encoding from plugin: {e}"))
-    })?;
+    child_stdout
+        .read_exact(&mut length_buf)
+        .map_err(|e| ShellError::PluginFailedToLoad {
+            msg: format!("unable to get encoding from plugin: {e}"),
+        })?;
 
     let mut buf = vec![0u8; length_buf[0] as usize];
-    child_stdout.read_exact(&mut buf).map_err(|e| {
-        ShellError::PluginFailedToLoad(format!("unable to get encoding from plugin: {e}"))
-    })?;
+    child_stdout
+        .read_exact(&mut buf)
+        .map_err(|e| ShellError::PluginFailedToLoad {
+            msg: format!("unable to get encoding from plugin: {e}"),
+        })?;
 
     EncodingType::try_from_bytes(&buf).ok_or_else(|| {
         let encoding_for_debug = String::from_utf8_lossy(&buf);
-        ShellError::PluginFailedToLoad(format!(
-            "get unsupported plugin encoding: {encoding_for_debug}"
-        ))
+        ShellError::PluginFailedToLoad {
+            msg: format!("get unsupported plugin encoding: {encoding_for_debug}"),
+        }
     })
 }

crates/nu-plugin/src/protocol/mod.rs

@@ -83,7 +83,7 @@ impl From<ShellError> for LabeledError {
                 msg: format!("did you mean '{suggestion}'?"),
                 span: Some(span),
             },
-            ShellError::PluginFailedToLoad(msg) => LabeledError {
+            ShellError::PluginFailedToLoad { msg } => LabeledError {
                 label: "Plugin failed to load".into(),
                 msg,
                 span: None,

crates/nu-plugin/src/protocol/plugin_custom_value.rs

@@ -68,9 +68,9 @@ impl CustomValue for PluginCustomValue {
             let stdout_reader = match &mut child.stdout {
                 Some(out) => out,
                 None => {
-                    return Err(ShellError::PluginFailedToLoad(
-                        "Plugin missing stdout reader".into(),
-                    ))
+                    return Err(ShellError::PluginFailedToLoad {
+                        msg: "Plugin missing stdout reader".into(),
+                    })
                 }
             };
             get_plugin_encoding(stdout_reader)?