Sema: validate deref operator type and value

src/AstGen.zig

@@ -812,6 +812,7 @@ fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerEr
 
         .deref => {
             const lhs = try expr(gz, scope, .none, node_datas[node].lhs);
+            _ = try gz.addUnTok(.validate_deref, lhs, main_tokens[node]);
             switch (rl) {
                 .ref => return lhs,
                 else => {
@@ -2500,6 +2501,7 @@ fn unusedResultExpr(gz: *GenZir, scope: *Scope, statement: Ast.Node.Index) Inner
             .memset,
             .validate_array_init_ty,
             .validate_struct_init_ty,
+            .validate_deref,
             => break :b true,
         }
     } else switch (maybe_unused_result) {

src/Sema.zig

@@ -1080,6 +1080,11 @@ fn analyzeBodyInner(
                 i += 1;
                 continue;
             },
+            .validate_deref => {
+                try sema.zirValidateDeref(block, inst);
+                i += 1;
+                continue;
+            },
             .@"export" => {
                 try sema.zirExport(block, inst);
                 i += 1;
@@ -3849,6 +3854,28 @@ fn zirValidateArrayInit(
     }
 }
 
+fn zirValidateDeref(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
+    const inst_data = sema.code.instructions.items(.data)[inst].un_tok;
+    const src = inst_data.src();
+    const operand_src: LazySrcLoc = .{ .token_offset = inst_data.src_tok + 1 };
+    const operand = try sema.resolveInst(inst_data.operand);
+    const operand_ty = sema.typeOf(operand);
+
+    if (operand_ty.zigTypeTag() != .Pointer) {
+        return sema.fail(block, src, "cannot dereference non-pointer type '{}'", .{operand_ty.fmt(sema.mod)});
+    } else switch (operand_ty.ptrSize()) {
+        .One, .C => {},
+        .Many => return sema.fail(block, src, "index syntax required for unknown-length pointer type '{}'", .{operand_ty.fmt(sema.mod)}),
+        .Slice => return sema.fail(block, src, "index syntax required for slice type '{}'", .{operand_ty.fmt(sema.mod)}),
+    }
+
+    if (try sema.resolveMaybeUndefVal(block, operand_src, operand)) |val| {
+        if (val.isUndef()) {
+            return sema.fail(block, src, "cannot dereference undefined value", .{});
+        }
+    }
+}
+
 fn failWithBadMemberAccess(
     sema: *Sema,
     block: *Block,

src/Zir.zig

@@ -729,6 +729,9 @@ pub const Inst = struct {
         /// Same as `validate_array_init` but additionally communicates that the
         /// resulting array initialization value is within a comptime scope.
         validate_array_init_comptime,
+        /// Check that operand type supports the dereference operand (.*).
+        /// Uses the `un_tok` field.
+        validate_deref,
         /// A struct literal with a specified type, with no fields.
         /// Uses the `un_node` field.
         struct_init_empty,
@@ -1156,6 +1159,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime,
                 .validate_array_init,
                 .validate_array_init_comptime,
+                .validate_deref,
                 .struct_init_empty,
                 .struct_init,
                 .struct_init_ref,
@@ -1309,6 +1313,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime,
                 .validate_array_init,
                 .validate_array_init_comptime,
+                .validate_deref,
                 .@"export",
                 .export_value,
                 .set_cold,
@@ -1709,6 +1714,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime = .pl_node,
                 .validate_array_init = .pl_node,
                 .validate_array_init_comptime = .pl_node,
+                .validate_deref = .un_tok,
                 .struct_init_empty = .un_node,
                 .field_type = .pl_node,
                 .field_type_ref = .pl_node,

src/print_zir.zig

@@ -242,6 +242,7 @@ const Writer = struct {
             .ret_tok,
             .ensure_err_payload_void,
             .closure_capture,
+            .validate_deref,
             => try self.writeUnTok(stream, inst),
 
             .bool_br_and,