From 483b3a334487a60320296b876c12ccfc05d4a9fb Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Tue, 19 Sep 2023 19:16:17 -0700
Subject: [PATCH] InternPool: implement only_possible_value prong of indexToKey

for the new struct and packed struct encodings.
---
 src/InternPool.zig | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/src/InternPool.zig b/src/InternPool.zig
index c5eaa41ead..2fb0b11088 100644
--- a/src/InternPool.zig
+++ b/src/InternPool.zig
@@ -3859,7 +3859,7 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
         .func_decl => .{ .func = ip.extraFuncDecl(data) },
         .func_coerced => .{ .func = ip.extraFuncCoerced(data) },
         .only_possible_value => {
-            const ty = @as(Index, @enumFromInt(data));
+            const ty: Index = @enumFromInt(data);
             const ty_item = ip.items.get(@intFromEnum(ty));
             return switch (ty_item.tag) {
                 .type_array_big => {
@@ -3872,20 +3872,33 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
                         .storage = .{ .elems = sentinel[0..@intFromBool(sentinel[0] != .none)] },
                     } };
                 },
-                .type_array_small, .type_vector => .{ .aggregate = .{
-                    .ty = ty,
-                    .storage = .{ .elems = &.{} },
-                } },
-                // TODO: migrate structs to properly use the InternPool rather
-                // than using the SegmentedList trick, then the struct type will
-                // have a slice of comptime values that can be used here for when
-                // the struct has one possible value due to all fields comptime (same
-                // as the tuple case below).
-                .type_struct, .type_struct_ns => .{ .aggregate = .{
+                .type_array_small,
+                .type_vector,
+                .type_struct_ns,
+                .type_struct_packed,
+                => .{ .aggregate = .{
                     .ty = ty,
                     .storage = .{ .elems = &.{} },
                 } },
 
+                // There is only one possible value precisely due to the
+                // fact that this values slice is fully populated!
+                .type_struct => {
+                    const info = extraStructType(ip, ty_item.data);
+                    return .{ .aggregate = .{
+                        .ty = ty,
+                        .storage = .{ .elems = @ptrCast(info.field_inits.get(ip)) },
+                    } };
+                },
+
+                .type_struct_packed_inits => {
+                    const info = extraPackedStructType(ip, ty_item.data, true);
+                    return .{ .aggregate = .{
+                        .ty = ty,
+                        .storage = .{ .elems = @ptrCast(info.field_inits.get(ip)) },
+                    } };
+                },
+
                 // There is only one possible value precisely due to the
                 // fact that this values slice is fully populated!
                 .type_struct_anon, .type_tuple_anon => {
@@ -3898,11 +3911,6 @@ pub fn indexToKey(ip: *const InternPool, index: Index) Key {
                     } };
                 },
 
-                .type_struct_packed, .type_struct_packed_inits => {
-                    // a packed struct has a 0-bit backing type
-                    @panic("TODO");
-                },
-
                 .type_enum_auto,
                 .type_enum_explicit,
                 .type_union,