From 943176bbfcf3125451fa64e082ee357c28e70413 Mon Sep 17 00:00:00 2001
From: Will Lillis <wlillis@umass.edu>
Date: Mon, 23 Sep 2024 16:04:24 -0400
Subject: [PATCH] fix: Add error note when attempt is made to destructure error
 union (#21491)

closes #21417
---
 src/Sema.zig                                      |  3 +++
 .../compile_errors/destructure_error_union.zig    | 15 +++++++++++++++
 2 files changed, 18 insertions(+)
 create mode 100644 test/cases/compile_errors/destructure_error_union.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 14a4061b00..40556d2136 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -5428,6 +5428,9 @@ fn zirValidateDestructure(sema: *Sema, block: *Block, inst: Zir.Inst.Index) Comp
             const msg = try sema.errMsg(src, "type '{}' cannot be destructured", .{operand_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(destructure_src, msg, "result destructured here", .{});
+            if (operand_ty.zigTypeTag(pt.zcu) == .error_union) {
+                try sema.errNote(src, msg, "consider using 'try', 'catch', or 'if'", .{});
+            }
             break :msg msg;
         });
     }
diff --git a/test/cases/compile_errors/destructure_error_union.zig b/test/cases/compile_errors/destructure_error_union.zig
new file mode 100644
index 0000000000..fb5872707d
--- /dev/null
+++ b/test/cases/compile_errors/destructure_error_union.zig
@@ -0,0 +1,15 @@
+pub export fn entry() void {
+    const Foo = struct { u8, u8 };
+    const foo: anyerror!Foo = error.Failure;
+    const bar, const baz = foo;
+    _ = bar;
+    _ = baz;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :4:28: error: type 'anyerror!tmp.entry.Foo' cannot be destructured
+// :4:26: note: result destructured here
+// :4:28: note: consider using 'try', 'catch', or 'if'