Remember whether a struct literal had syntax errors.

This adds a variant `NoneWithError` to AST and HIR representations of
the “rest” or “tail”, which is currently always treated identically to
the `None` variant.

clippy_lints/src/no_effect.rs

@@ -242,7 +242,7 @@ fn has_no_effect(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
             !expr_ty_has_significant_drop(cx, expr)
                 && fields.iter().all(|field| has_no_effect(cx, field.expr))
                 && match &base {
-                    StructTailExpr::None | StructTailExpr::DefaultFields(_) => true,
+                    StructTailExpr::None | StructTailExpr::NoneWithError(_) | StructTailExpr::DefaultFields(_) => true,
                     StructTailExpr::Base(base) => has_no_effect(cx, base),
                 }
         },
@@ -353,7 +353,7 @@ fn reduce_expression<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<Vec
             } else {
                 let base = match base {
                     StructTailExpr::Base(base) => Some(base),
-                    StructTailExpr::None | StructTailExpr::DefaultFields(_) => None,
+                    StructTailExpr::None | StructTailExpr::NoneWithError(_) | StructTailExpr::DefaultFields(_) => None,
                 };
                 Some(fields.iter().map(|f| &f.expr).chain(base).map(Deref::deref).collect())
             }

clippy_lints/src/utils/author.rs

@@ -673,7 +673,7 @@ macro_rules! kind {
                 bind!(self, qpath, fields);
                 let base = OptionPat::new(match base {
                     StructTailExpr::Base(base) => Some(self.bind("base", base)),
-                    StructTailExpr::None | StructTailExpr::DefaultFields(_) => None,
+                    StructTailExpr::None | StructTailExpr::NoneWithError(_) | StructTailExpr::DefaultFields(_) => None,
                 });
                 kind!("Struct({qpath}, {fields}, {base})");
                 self.qpath(qpath, &expr.name, expr.value.hir_id);