From de24cea2cff33654ee41369517144bb94f6d139d Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Fri, 9 Sep 2022 15:19:51 +0300
Subject: [PATCH] Sema: handle empty_struct_value in beginComptimePtrMutation

Closes #12794
---
 src/Sema.zig                 | 14 +++++++++++++
 test/behavior.zig            |  1 +
 test/behavior/bugs/12794.zig | 38 ++++++++++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+)
 create mode 100644 test/behavior/bugs/12794.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 1afecef461..d96363b160 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -24770,6 +24770,20 @@ fn beginComptimePtrMutation(
                         else => unreachable,
                     },
 
+                    .empty_struct_value => {
+                        const duped = try sema.arena.create(Value);
+                        duped.* = Value.initTag(.the_only_possible_value);
+                        return beginComptimePtrMutationInner(
+                            sema,
+                            block,
+                            src,
+                            parent.ty.structFieldType(field_index),
+                            duped,
+                            ptr_elem_ty,
+                            parent.decl_ref_mut,
+                        );
+                    },
+
                     else => unreachable,
                 },
                 .reinterpret => |reinterpret| {
diff --git a/test/behavior.zig b/test/behavior.zig
index db107bcbb1..e11cda3b27 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -87,6 +87,7 @@ test {
     _ = @import("behavior/bugs/12486.zig");
     _ = @import("behavior/bugs/12680.zig");
     _ = @import("behavior/bugs/12776.zig");
+    _ = @import("behavior/bugs/12794.zig");
     _ = @import("behavior/byteswap.zig");
     _ = @import("behavior/byval_arg_var.zig");
     _ = @import("behavior/call.zig");
diff --git a/test/behavior/bugs/12794.zig b/test/behavior/bugs/12794.zig
new file mode 100644
index 0000000000..530f81cff2
--- /dev/null
+++ b/test/behavior/bugs/12794.zig
@@ -0,0 +1,38 @@
+const std = @import("std");
+
+fn NamespacedComponents(comptime modules: anytype) type {
+    return @Type(.{
+        .Struct = .{
+            .layout = .Auto,
+            .is_tuple = false,
+            .fields = &.{.{
+                .name = "components",
+                .field_type = @TypeOf(modules.components),
+                .default_value = null,
+                .is_comptime = false,
+                .alignment = @alignOf(@TypeOf(modules.components)),
+            }},
+            .decls = &[_]std.builtin.Type.Declaration{},
+        },
+    });
+}
+
+fn namespacedComponents(comptime modules: anytype) NamespacedComponents(modules) {
+    var x: NamespacedComponents(modules) = undefined;
+    x.components = modules.components;
+    return x;
+}
+
+pub fn World(comptime modules: anytype) type {
+    const all_components = namespacedComponents(modules);
+    _ = all_components;
+    return struct {};
+}
+
+test {
+    _ = World(.{
+        .components = .{
+            .location = struct {},
+        },
+    });
+}