Propagate unrecoverable error to users when resolving aliases

src/bin/cargo/main.rs

@@ -1,6 +1,7 @@
 #![warn(rust_2018_idioms)] // while we're getting used to 2018
 #![allow(clippy::all)]
 
+use cargo::util::config::{ConfigError, ConfigErrorKind, Value};
 use cargo::util::toml::StringOrVec;
 use cargo::util::CliError;
 use cargo::util::{self, closest_msg, command_prelude, CargoResult, CliResult, Config};
@@ -52,18 +53,32 @@ fn builtin_aliases_execs(cmd: &str) -> Option<&(&str, &str, &str)> {
     BUILTIN_ALIASES.iter().find(|alias| alias.0 == cmd)
 }
 
+/// Resolve the aliased command from the [`Config`] with a given command string.
+///
+/// The search fallback chain is:
+///
+/// 1. Get the aliased command as a string.
+/// 2. If the aliased command is not a string, get it as an array.
+/// 3. If cannot find any, finds one insides [`BUILTIN_ALIASES`].
+/// 4. If still no command is found, return `None`.
 fn aliased_command(config: &Config, command: &str) -> CargoResult<Option<Vec<String>>> {
-    let alias_name = format!("alias.{}", command);
-    let user_alias = match config.get_string(&alias_name) {
-        Ok(Some(record)) => Some(
+    let alias_name = format!("alias.{command}");
+    let user_alias = match config.get::<Value<String>>(&alias_name) {
+        Ok(record) => Some(
             record
                 .val
                 .split_whitespace()
                 .map(|s| s.to_string())
                 .collect(),
         ),
-        Ok(None) => None,
-        Err(_) => config.get::<Option<Vec<String>>>(&alias_name)?,
+        Err(e) => match e.downcast_ref::<ConfigError>().map(|e| e.kind()) {
+            // Just report we cannot find anything.
+            Some(ConfigErrorKind::MissingKey) => None,
+            // Alias might be set as an toml array, fallback and try it.
+            Some(ConfigErrorKind::UnexpectedValue) => config.get::<Option<_>>(&alias_name)?,
+            // A unrecoverable error, e.g. TOML parsing error. Relay it to the user.
+            Some(ConfigErrorKind::Custom) | None => return Err(e),
+        },
     };
 
     let result = user_alias.or_else(|| {