reflect: remove comptime var pointer returns

Following ziglang/zig#19414 and
https://ziggit.dev/t/comptime-mutable-memory-changes/3702 change in zig,
we cannot return `comptime var` pointer anymore.

src/engines/v8/generate.zig

@@ -168,7 +168,7 @@ fn getNativeArg(
 
     // JS object
     const ptr = try getNativeObject(nat_ctx, T_refl, js_value.castTo(v8.Object));
-    if (arg_T.underPtr() != null) {
+    if (comptime arg_T.underPtr() != null) {
         value = ptr;
     } else {
         value = ptr.*;
@@ -389,13 +389,14 @@ fn getArgs(
 
 fn freeArgs(alloc: std.mem.Allocator, comptime func: refl.Func, obj: anytype) !void {
     inline for (func.args) |arg_T| {
+        const underT = comptime arg_T.underT();
 
         // free char slices
         // the API functions will be responsible of copying the slice
         // in their implementations if they want to keep it afterwards
-        if (arg_T.underT() == []u8 or arg_T.underT() == []const u8) {
+        if (underT == []u8 or underT == []const u8) {
             const val = @field(obj, arg_T.name.?);
-            if (arg_T.underOpt() != null) {
+            if (comptime arg_T.underOpt() != null) {
                 // free only if val is non-null
                 if (val) |v| {
                     alloc.free(v);
@@ -406,7 +407,7 @@ fn freeArgs(alloc: std.mem.Allocator, comptime func: refl.Func, obj: anytype) !v
         }
 
         // free varidadic slices
-        if (try refl.Type.variadic(arg_T.underT(), null) != null) {
+        if (try refl.Type.variadic(underT, null) != null) {
             const val = @field(obj, arg_T.name.?).?;
             // NOTE: variadic are optional by design
             alloc.free(@field(val, "slice"));
@@ -913,7 +914,7 @@ fn callFunc(
 
     // call native func
     const function = @field(T_refl.T, func.name);
-    const res_T = func.return_type.underErr() orelse func.return_type.T;
+    const res_T = comptime func.return_type.underErr() orelse func.return_type.T;
     var res: res_T = undefined;
     if (comptime @typeInfo(func.return_type.T) == .ErrorUnion) {
         res = @call(.auto, function, args) catch |err| {
@@ -940,7 +941,7 @@ fn callFunc(
             nat_ctx.alloc,
             nat_ctx,
             T_refl,
-            func.return_type.underT(),
+            comptime func.return_type.underT(),
             res,
             cbk_info.getThis(),
             isolate,

src/generate.zig

@@ -38,15 +38,16 @@ const loadFn = @import("private_api.zig").loadFn;
 // reflect the user-defined types to obtain type information (T_refl)
 // This function must be called at comptime by the root file of the project
 // and stored in a constant named `Types`
-pub fn reflect(comptime types: anytype) []refl.Struct {
+pub fn reflect(comptime types: anytype) []const refl.Struct {
     std.debug.assert(@inComptime());
 
     // call types reflection
-    return refl.do(types) catch unreachable;
+    const structs: []const refl.Struct = refl.do(types) catch |e| @compileError(@errorName(e));
+    return structs;
 }
 
 // Import user-defined types
-pub const Types: []refl.Struct = @import("root").Types;
+pub const Types: []const refl.Struct = @import("root").Types;
 
 // retrieved the reflected type of a user-defined native type
 pub fn getType(comptime T: type) refl.Struct {
@@ -61,7 +62,7 @@ pub fn getType(comptime T: type) refl.Struct {
 
 // generate APIs from reflected types
 // which can be later loaded in JS.
-fn generate(comptime types: []refl.Struct) []API {
+fn generate(comptime types: []const refl.Struct) []API {
     std.debug.assert(@inComptime());
 
     var apis: [types.len]API = undefined;