fix: clearer unused var warning closes #579

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 ### Fixed
 
+- **aiken-lang**: Explain discards and expect a bit better in the unused var warning
 - **aiken-lang**: Fix expect \_ = ... not including the cast from data logic if the type is data and right hand has a type annotation
 - **aiken-lang**: Fix for the final clause of a when expecting another clause
   afterwards in nested list cases.

crates/aiken-lang/src/tipo/error.rs

@@ -1426,16 +1426,17 @@ pub enum Warning {
         name.if_supports_color(Stderr, |s| s.purple())
     )]
     #[diagnostic(help("{}", formatdoc! {
-        r#"No big deal, but you might want to remove it to get rid of that warning.
+        r#"No big deal, but you might want to remove it or use a discard {name} to get rid of that warning.
 
            You should also know that, unlike in typical imperative languages, unused let-bindings are {fully_ignored} in Aiken.
            They will not produce any side-effect (such as error calls). Programs with or without unused variables are semantically equivalent.
 
-           If you do want to enforce some side-effects, use {keyword_expect} instead of {keyword_let}.
+           If you do want to enforce some side-effects, use {keyword_expect} with a discard {name} instead of {keyword_let}.
         "#,
         fully_ignored = "fully_ignored".if_supports_color(Stderr, |s| s.bold()),
         keyword_expect = "expect".if_supports_color(Stderr, |s| s.yellow()),
         keyword_let = "let".if_supports_color(Stderr, |s| s.yellow()),
+        name = format!("_{name}").if_supports_color(Stderr, |s| s.yellow())
     }))]
     #[diagnostic(code("unused::variable"))]
     UnusedVariable {