feat(tvix/eval): skip & warn for useless parenthesis r/5607

Change-Id: I567ca0682012b9d09f1217e57a104ac5671f8d82
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7771
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 26 insertions, 0 deletions

diff --git a/tvix/eval/src/compiler/optimiser.rs b/tvix/eval/src/compiler/optimiser.rs
index 615de32357..af0ad2256e 100644
--- a/tvix/eval/src/compiler/optimiser.rs
+++ b/tvix/eval/src/compiler/optimiser.rs
@@ -9,6 +9,7 @@ use ast::Expr;
 pub(super) fn optimise_expr(c: &mut Compiler, slot: LocalIdx, expr: ast::Expr) -> ast::Expr {
     match expr {
         Expr::BinOp(_) => optimise_bin_op(c, slot, expr),
+        Expr::Paren(_) => optimise_paren(c, expr),
         _ => expr.to_owned(),
     }
 }
@@ -123,3 +124,28 @@ fn optimise_bin_op(c: &mut Compiler, slot: LocalIdx, expr: ast::Expr) -> ast::Ex
 
     expr
 }
+
+/// Detect useless parenthesis around primitive expressions.
+fn optimise_paren(c: &mut Compiler, expr: ast::Expr) -> ast::Expr {
+    if let Expr::Paren(inner) = &expr {
+        let inner = inner.expr().unwrap();
+
+        if let Expr::Paren(_) = &inner {
+            c.emit_warning(&expr, WarningKind::UselessParens);
+            return optimise_paren(c, inner);
+        }
+
+        if let Expr::Literal(_)
+        | Expr::Str(_)
+        | Expr::Select(_)
+        | Expr::List(_)
+        | Expr::AttrSet(_)
+        | Expr::Ident(_) = &inner
+        {
+            c.emit_warning(&expr, WarningKind::UselessParens);
+            return inner;
+        }
+    }
+
+    expr
+}