From 86a75b35deaa465aa45042dbc6b64a470d404b7a Mon Sep 17 00:00:00 2001
From: Lukas Neubert <lukas.neubert@proton.me>
Date: Wed, 20 Dec 2023 20:59:57 +0100
Subject: [PATCH] checker: prevent invalid SelectorExprs

---
 CHANGELOG.md                                 | 1 +
 lib/bait/checker/expr.bt                     | 3 ++-
 lib/bait/preference/preference.bt            | 2 +-
 tests/out/error/selector/cannot_select.in.bt | 7 +++++++
 tests/out/error/selector/cannot_select.out   | 1 +
 5 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 tests/out/error/selector/cannot_select.in.bt
 create mode 100644 tests/out/error/selector/cannot_select.out

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6ca38c13..67952a8f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@ _unreleased_
 ### Error and Type Checks
 - If conditions must be of type bool
 - Cannot assign from a void function call
+- Prevent selecting fields of unsupported types (e.g. enums)
 - Prevent some cases of identifier redefinition
   - Any identifier by a function name
   - Function argument by a variable
diff --git a/lib/bait/checker/expr.bt b/lib/bait/checker/expr.bt
index 86c67d10..6cfb9dfb 100644
--- a/lib/bait/checker/expr.bt
+++ b/lib/bait/checker/expr.bt
@@ -347,7 +347,8 @@ fun (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 		return ast.VOID_TYPE
 	}
 
-	return ast.ANY_TYPE
+	c.error('cannot select from ${c.table.type_name(node.expr_type)}', node.pos)
+	return ast.PLACEHOLDER_TYPE
 }
 
 fun (c Checker) string_literal(node ast.StringLiteral) ast.Type {
diff --git a/lib/bait/preference/preference.bt b/lib/bait/preference/preference.bt
index fb50bf1c..be28ee1d 100644
--- a/lib/bait/preference/preference.bt
+++ b/lib/bait/preference/preference.bt
@@ -164,7 +164,7 @@ fun backend_from_string(s string) Backend {
 		'c' { .c }
 		else {
 			panic('Invalid backend: ${s}')
-			.js
+			Backend.js // TODO remove once @noreturn works properly
 		}
 	}
 }
diff --git a/tests/out/error/selector/cannot_select.in.bt b/tests/out/error/selector/cannot_select.in.bt
new file mode 100644
index 00000000..75a54067
--- /dev/null
+++ b/tests/out/error/selector/cannot_select.in.bt
@@ -0,0 +1,7 @@
+enum Color {
+	red
+	green
+}
+
+c := Color.red
+_ := c.my_field
diff --git a/tests/out/error/selector/cannot_select.out b/tests/out/error/selector/cannot_select.out
new file mode 100644
index 00000000..0548d522
--- /dev/null
+++ b/tests/out/error/selector/cannot_select.out
@@ -0,0 +1 @@
+tests/out/error/selector/cannot_select.in.bt:7:7 error: cannot select from Color