From 8841a71aa675f76c0ff7658339872a5faa5e4d5b Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sat, 19 Feb 2022 15:08:59 -0700
Subject: [PATCH] AstGen: evaluate `comptime var` init expressions in a
 comptime context

---
 lib/std/fmt.zig |  1 -
 src/AstGen.zig  | 17 ++++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index 240a3ad233..b6594f193c 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -77,7 +77,6 @@ pub fn format(
 ) !void {
     const ArgsType = @TypeOf(args);
     const args_type_info = @typeInfo(ArgsType);
-    // XXX: meta.trait.is(.Struct)(ArgsType) doesn't seem to work...
     if (args_type_info != .Struct) {
         @compileError("Expected tuple or struct argument, found " ++ @typeName(ArgsType));
     }
diff --git a/src/AstGen.zig b/src/AstGen.zig
index 0652a6232f..bf34ce4780 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -319,6 +319,21 @@ fn reachableExpr(
     node: Ast.Node.Index,
     reachable_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
+    return reachableExprComptime(gz, scope, rl, node, reachable_node, false);
+}
+
+fn reachableExprComptime(
+    gz: *GenZir,
+    scope: *Scope,
+    rl: ResultLoc,
+    node: Ast.Node.Index,
+    reachable_node: Ast.Node.Index,
+    force_comptime: bool,
+) InnerError!Zir.Inst.Ref {
+    const prev_force_comptime = gz.force_comptime;
+    gz.force_comptime = prev_force_comptime or force_comptime;
+    defer gz.force_comptime = prev_force_comptime;
+
     const result_inst = try expr(gz, scope, rl, node);
     if (gz.refIsNoReturn(result_inst)) {
         try gz.astgen.appendErrorNodeNotes(reachable_node, "unreachable code", .{}, &[_]u32{
@@ -2758,7 +2773,7 @@ fn varDecl(
                 resolve_inferred_alloc = alloc;
                 break :a .{ .alloc = alloc, .result_loc = .{ .inferred_ptr = alloc } };
             };
-            _ = try reachableExpr(gz, scope, var_data.result_loc, var_decl.ast.init_node, node);
+            _ = try reachableExprComptime(gz, scope, var_data.result_loc, var_decl.ast.init_node, node, is_comptime);
             if (resolve_inferred_alloc != .none) {
                 _ = try gz.addUnNode(.resolve_inferred_alloc, resolve_inferred_alloc, node);
             }