Add fnm default to return default version

docs/commands.md

@@ -14,7 +14,7 @@ Commands:
   completions  Print shell completions to stdout
   alias        Alias a version to a common name
   unalias      Remove an alias definition
-  default      Set a version as the default version
+  default      Set a version as the default version or get the current default version
   current      Print the current Node.js version
   exec         Run a command within fnm context
   uninstall    Uninstall a Node.js version
@@ -607,14 +607,14 @@ Options:
 # `fnm default`
 
 ```
-Set a version as the default version
+Set a version as the default version or get the current default version.
 
 This is a shorthand for `fnm alias VERSION default`
 
-Usage: fnm default [OPTIONS] <VERSION>
+Usage: fnm default [OPTIONS] [VERSION]
 
 Arguments:
-  <VERSION>
+  [VERSION]
 
 
 Options:

src/alias.rs

@@ -30,6 +30,11 @@ pub fn list_aliases(config: &FnmConfig) -> std::io::Result<Vec<StoredAlias>> {
     Ok(vec)
 }
 
+pub fn get_alias_by_name(config: &FnmConfig, alias_name: &str) -> Option<StoredAlias> {
+    let alias_path = config.aliases_dir().join(alias_name);
+    TryInto::<StoredAlias>::try_into(alias_path.as_path()).ok()
+}
+
 #[derive(Debug)]
 pub struct StoredAlias {
     alias_path: PathBuf,

src/cli.rs

@@ -44,7 +44,7 @@ pub enum SubCommand {
     #[clap(name = "unalias", bin_name = "unalias")]
     Unalias(commands::unalias::Unalias),
 
-    /// Set a version as the default version
+    /// Set a version as the default version or get the current default version.
     ///
     /// This is a shorthand for `fnm alias VERSION default`
     #[clap(name = "default", bin_name = "default")]

src/commands/alias.rs

@@ -38,4 +38,6 @@ pub enum Error {
     VersionNotFound { version: UserVersion },
     #[error(transparent)]
     CantUnderstandVersion { source: ApplicableVersionError },
+    #[error("A default version has not been set.")]
+    DefaultAliasDoesNotExist,
 }

src/commands/default.rs

@@ -1,22 +1,34 @@
 use super::alias::Alias;
 use super::command::Command;
+use crate::alias::get_alias_by_name;
 use crate::config::FnmConfig;
 use crate::user_version::UserVersion;
 
 #[derive(clap::Parser, Debug)]
 pub struct Default {
-    version: UserVersion,
+    version: Option<UserVersion>,
 }
 
 impl Command for Default {
     type Error = super::alias::Error;
 
     fn apply(self, config: &FnmConfig) -> Result<(), Self::Error> {
-        Alias {
-            name: "default".into(),
-            to_version: self.version,
+        match self.version {
+            Some(version) => Alias {
+                name: "default".into(),
+                to_version: version,
+            }
+            .apply(config),
+            None => {
+                match get_alias_by_name(config, "default") {
+                    Some(alias) => {
+                        println!("{}", alias.s_ver());
+                        return Ok(());
+                    }
+                    None => Err(Self::Error::DefaultAliasDoesNotExist),
+                }
+            }
         }
-        .apply(config)
     }
 
     fn handle_error(err: Self::Error, config: &FnmConfig) {