feat: check multiple receipt paths

We now check multiple receipt paths, including XDG_CONFIG_HOME.
We load a receipt from the first path which contains a receipt file,
ensuring we're able to manage the absence of a receipt in that path
if that environment variable is set.

axoupdater/src/errors.rs

@@ -85,6 +85,16 @@ pub enum AxoupdateError {
         app_name: String,
     },
 
+    /// Not a generic receipt load failure, but the receipt itself doesn't exist.
+    #[error("Unable to load receipt for app {app_name}")]
+    #[diagnostic(help(
+        "This may indicate that this installation of {app_name} was installed via a method that's not eligible for upgrades."
+    ))]
+    NoReceipt {
+        /// This app's name
+        app_name: String,
+    },
+
     /// Indicates that this app's name couldn't be determined when trying
     /// to autodetect it.
     #[error("Unable to determine the name of the app to update")]

axoupdater/src/receipt.rs

@@ -116,49 +116,69 @@ impl AxoUpdater {
     }
 }
 
-pub(crate) fn get_config_path(app_name: &str) -> AxoupdateResult<Utf8PathBuf> {
+/// Returns a Vec of possible receipt locations, beginning with
+/// `XDG_CONFIG_HOME` (if set).
+pub(crate) fn get_config_paths(app_name: &str) -> AxoupdateResult<Vec<Utf8PathBuf>> {
+    let mut potential_homes = vec![];
+
     if env::var("AXOUPDATER_CONFIG_WORKING_DIR").is_ok() {
-        Ok(Utf8PathBuf::try_from(current_dir()?)?)
+        Ok(vec![Utf8PathBuf::try_from(current_dir()?)?])
     } else if let Ok(path) = env::var("AXOUPDATER_CONFIG_PATH") {
-        Ok(Utf8PathBuf::from(path))
+        Ok(vec![Utf8PathBuf::from(path)])
     } else {
         let xdg_home = env::var("XDG_CONFIG_HOME")
             .ok()
-            .map(PathBuf::from)
+            .map(Utf8PathBuf::from)
             .map(|h| h.join(app_name));
-        let xdg_home_exists = xdg_home.as_ref().map(|h| h.exists()).unwrap_or(false);
-
+        if let Some(home) = &xdg_home {
+            if home.exists() {
+                potential_homes.push(home.to_owned());
+            }
+        }
         let home = if cfg!(windows) {
             env::var("LOCALAPPDATA")
                 .map(PathBuf::from)
                 .map(|h| h.join(app_name))
                 .ok()
-        } else if xdg_home_exists {
-            xdg_home
         } else {
             homedir::my_home()?.map(|path| path.join(".config").join(app_name))
         };
-        let Some(home) = home else {
+        if let Some(home) = home {
+            potential_homes.push(Utf8PathBuf::try_from(home)?);
+        }
+
+        if potential_homes.is_empty() {
             return Err(AxoupdateError::NoHome {});
-        };
+        }
 
-        Ok(Utf8PathBuf::try_from(home)?)
+        Ok(potential_homes)
     }
 }
 
+/// Iterates through the list of possible receipt locations from
+/// `get_config_paths` and returns the first that contains a valid receipt.
+pub(crate) fn get_receipt_path(app_name: &str) -> AxoupdateResult<Option<Utf8PathBuf>> {
+    for receipt_prefix in get_config_paths(app_name)? {
+        let install_receipt_path = receipt_prefix.join(format!("{app_name}-receipt.json"));
+        if install_receipt_path.exists() {
+            return Ok(Some(install_receipt_path));
+        }
+    }
+
+    Ok(None)
+}
+
 fn load_receipt_from_path(install_receipt_path: &Utf8PathBuf) -> AxoupdateResult<InstallReceipt> {
     Ok(SourceFile::load_local(install_receipt_path)?.deserialize_json()?)
 }
 
 fn load_receipt_for(app_name: &str) -> AxoupdateResult<InstallReceipt> {
-    let Ok(receipt_prefix) = get_config_path(app_name) else {
-        return Err(AxoupdateError::ConfigFetchFailed {
+    let Some(install_receipt_path) = get_receipt_path(app_name)? else {
+        return Err(AxoupdateError::NoReceipt {
             app_name: app_name.to_owned(),
         });
     };
 
-    let install_receipt_path = receipt_prefix.join(format!("{app_name}-receipt.json"));
-
     load_receipt_from_path(&install_receipt_path).map_err(|_| AxoupdateError::ReceiptLoadFailed {
         app_name: app_name.to_owned(),
     })

axoupdater/src/test/helpers.rs

@@ -3,7 +3,7 @@ use std::{
     process::{Command, Stdio},
 };
 
-use crate::{receipt::get_config_path, ReleaseSourceType};
+use crate::{receipt::get_receipt_path, ReleaseSourceType};
 
 static RECEIPT_TEMPLATE: &str = r#"{"binaries":[BINARIES],"install_prefix":"INSTALL_PREFIX","provider":{"source":"cargo-dist","version":"0.10.0-prerelease.1"},"source":{"app_name":"APP_NAME","name":"PACKAGE","owner":"OWNER","release_type":"RELEASE_TYPE"},"version":"VERSION"}"#;
 
@@ -104,7 +104,10 @@ pub fn perform_runtest(runtest_args: &RuntestArgs) -> PathBuf {
     let app_home = &home.join(".cargo").join("bin");
     let app_path = &app_home.join(basename);
 
-    let config_path = get_config_path(app_name).unwrap().into_std_path_buf();
+    let config_path = get_receipt_path(app_name)
+        .unwrap()
+        .unwrap()
+        .into_std_path_buf();
 
     // Ensure we delete any previous copy that may exist
     // at this path before we copy in our version.