Change UnusedError to Warning

compiler/erg_compiler/error.rs

@@ -18,7 +18,7 @@ use erg_parser::error::{ParserRunnerError, ParserRunnerErrors};
 
 use crate::context::Context;
 use crate::hir::{Expr, Identifier, Signature};
-use crate::ty::{Predicate, Type};
+use crate::ty::{HasType, Predicate, Type};
 
 pub fn ordinal_num(n: usize) -> String {
     match n.to_string().chars().last().unwrap() {
@@ -109,7 +109,7 @@ pub fn readable_name(name: &str) -> &str {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct CompileError {
     pub core: Box<ErrorCore>, // ErrorCore is large, so box it
     pub input: Input,
@@ -1458,6 +1458,33 @@ impl LowerError {
         )
     }
 
+    pub fn unused_expr_warning(input: Input, errno: usize, expr: &Expr, caused_by: String) -> Self {
+        let desc = switch_lang!(
+            "japanese" => format!("式の評価結果(: {})が使われていません", expr.ref_t()),
+            "simplified_chinese" => format!("表达式评估结果(: {})未使用", expr.ref_t()),
+            "traditional_chinese" => format!("表達式評估結果(: {})未使用", expr.ref_t()),
+            "english" => format!("the evaluation result of the expression (: {}) is not used", expr.ref_t()),
+        );
+        let hint = switch_lang!(
+            "japanese" => "値を使わない場合は、discard関数を使用してください",
+            "simplified_chinese" => "如果您不想使用该值，请使用discard函数",
+            "traditional_chinese" => "如果您不想使用該值，請使用discard函數",
+            "english" => "if you don't use the value, use discard function",
+        )
+        .to_owned();
+        Self::new(
+            ErrorCore::new(
+                vec![SubMessage::ambiguous_new(expr.loc(), vec![], Some(hint))],
+                desc,
+                errno,
+                UnusedWarning,
+                expr.loc(),
+            ),
+            input,
+            caused_by,
+        )
+    }
+
     pub fn duplicate_decl_error(
         input: Input,
         errno: usize,
@@ -2234,7 +2261,7 @@ impl LowerError {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct CompileErrors(Vec<CompileError>);
 
 impl std::error::Error for CompileErrors {}