infer version from current system state for shim

src/current_version.rs

@@ -1,12 +1,43 @@
+use std::path::Path;
+
 use thiserror::Error;
 
 use crate::config::FnmConfig;
-use crate::system_version;
 use crate::version::Version;
+use crate::{default_version, installed_versions, system_version, version_files};
 
 pub fn current_version(config: &FnmConfig) -> Result<Option<Version>, Error> {
-    let multishell_path = config.multishell_path().ok_or(Error::EnvNotApplied)?;
+    match config.multishell_path() {
+        None => infer_current_version(config),
+        Some(multishell_path) => current_version_from_multishell(config, multishell_path),
+    }
+}
+
+/// infer the current version from the system state,
+/// by looking at the installed versions, the current working
+/// directory and the default version
+fn infer_current_version(config: &FnmConfig) -> Result<Option<Version>, Error> {
+    let current_directory =
+        std::env::current_dir().map_err(|err| Error::CantAccessCurrentDirectory { source: err })?;
+
+    if let Some(version) = version_files::get_user_version_for_directory(current_directory, config)
+    {
+        let all_versions = installed_versions::list(config.installations_dir())
+            .map_err(|source| Error::VersionListingError { source })?;
+        return Ok(version.to_version(&all_versions, config).cloned());
+    }
+
+    if let Some(version) = default_version::find_default_version(config) {
+        return Ok(Some(version));
+    }
+
+    return Ok(None);
+}
 
+fn current_version_from_multishell(
+    _config: &FnmConfig,
+    multishell_path: &Path,
+) -> Result<Option<Version>, Error> {
     if multishell_path.read_link().ok() == Some(system_version::path()) {
         return Ok(Some(Version::Bypassed));
     }
@@ -32,11 +63,13 @@ pub fn current_version(config: &FnmConfig) -> Result<Option<Version>, Error> {
 
 #[derive(Debug, Error)]
 pub enum Error {
-    #[error("`fnm env` was not applied in this context.\nCan't find fnm's environment variables")]
-    EnvNotApplied,
     #[error("Can't read the version as a valid semver")]
     VersionError {
         source: semver::Error,
         version: String,
     },
+    #[error("Can't access current directory")]
+    CantAccessCurrentDirectory { source: std::io::Error },
+    #[error("Can't list versions")]
+    VersionListingError { source: installed_versions::Error },
 }