Don't emit error when import ZON result type is not known

This will now instead trip an assert, as support for the .none result
type is not yet implemented

Author: MasonRemaley

src/Sema.zig

@@ -14044,14 +14044,13 @@ fn zirImport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.
             return Air.internedToRef(ty);
         },
         .zon => {
-            if (extra.res_ty == .none) {
-                return sema.fail(block, operand_src, "'@import' of ZON must have a known result type", .{});
-            }
-            const res_ty_inst = try sema.resolveInst(extra.res_ty);
-            const res_ty = try sema.analyzeAsType(block, operand_src, res_ty_inst);
-            if (res_ty.isGenericPoison()) {
-                return sema.fail(block, operand_src, "'@import' of ZON must have a known result type", .{});
-            }
+            const res_ty: InternPool.Index = b: {
+                if (extra.res_ty == .none) break :b .none;
+                const res_ty_inst = try sema.resolveInst(extra.res_ty);
+                const res_ty = try sema.analyzeAsType(block, operand_src, res_ty_inst);
+                if (res_ty.isGenericPoison()) break :b .none;
+                break :b res_ty.toIntern();
+            };
 
             try sema.declareDependency(.{ .zon_file = result.file_index });
             const interned = try LowerZon.run(

src/Sema/LowerZon.zig

@@ -33,7 +33,7 @@ pub fn run(
     sema: *Sema,
     file: *File,
     file_index: Zcu.File.Index,
-    res_ty: Type,
+    res_ty: InternPool.Index,
     import_loc: LazySrcLoc,
     block: *Sema.Block,
 ) CompileError!InternPool.Index {
@@ -53,9 +53,9 @@ pub fn run(
         .base_node_inst = tracked_inst,
     };
 
-    try lower_zon.checkType(res_ty);
+    try lower_zon.checkType(.fromInterned(res_ty));
 
-    return lower_zon.lowerExpr(.root, res_ty);
+    return lower_zon.lowerExpr(.root, .fromInterned(res_ty));
 }
 
 /// Validate that `ty` is a valid ZON type. If not, emit a compile error.