Commit `e2509ddbe6`

Veikka Tuominen <git@vexu.eu>

2022-12-02 19:16:47

AstGen: add error for invalid string comparisons

These operations are allowed because the string literals are just pointers but they produce unexpected results. These errors prevent beginners from shooting themselves in the foot while still allowing advanced users to circumvent them if they desire to do so. Closes #8290

master

1 parent 0e38cc1

Changed files (3)

src

AstGen.zig

test

cases

compile_errors

invalid_compare_string.zig

switch_on_slice.zig

@@ -5628,6 +5628,14 @@ fn simpleBinOp(
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
+    if (op_inst_tag == .cmp_neq or op_inst_tag == .cmp_eq) {
+        const node_tags = tree.nodes.items(.tag);
+        const str = if (op_inst_tag == .cmp_eq) "==" else "!=";
+        if (node_tags[node_datas[node].lhs] == .string_literal or
+            node_tags[node_datas[node].rhs] == .string_literal)
+            return astgen.failNode(node, "cannot compare strings with {s}", .{str});
+    }
+
     const lhs = try reachableExpr(gz, scope, .{ .rl = .none }, node_datas[node].lhs, node);
     var line: u32 = undefined;
     var column: u32 = undefined;
@@ -6625,6 +6633,11 @@ fn switchExpr(
             continue;
         }
 
+        for (case.ast.values) |val| {
+            if (node_tags[val] == .string_literal)
+                return astgen.failNode(val, "cannot switch on strings", .{});
+        }
+
         if (case.ast.values.len == 1 and node_tags[case.ast.values[0]] != .switch_range) {
             scalar_cases_len += 1;
         } else {

@@ -0,0 +1,29 @@
+comptime {
+    var a = "foo";
+    if (a == "foo") unreachable;
+}
+comptime {
+    var a = "foo";
+    if (a == ("foo")) unreachable; // intentionally allow
+}
+comptime {
+    var a = "foo";
+    switch (a) {
+        "foo" => unreachable,
+        else => {},
+    }
+}
+comptime {
+    var a = "foo";
+    switch (a) {
+        ("foo") => unreachable, // intentionally allow
+        else => {},
+    }
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:11: error: cannot compare strings with ==
+// :12:9: error: cannot switch on strings

@@ -1,7 +1,7 @@
 pub export fn entry() void {
     var a: [:0]const u8 = "foo";
     switch (a) {
-        "--version", "version" => unreachable,
+        ("--version"), ("version") => unreachable,
         else => {},
     }
 }

Commit e2509ddbe6

Commit `e2509ddbe6`