[ts] erroneous mutable API generated for boolean fields in structs

[nurbo]

I came across a missing boolean/number conversion issue when compiling files with generated mutable APIs (--gen-mutable flag).

Given the following schema:

struct s {
  flag: bool;
}

table t {
  flag: bool;
}

Compiled with flatc (version 25.2.10):

> flatc --ts --gen-mutable -o ./tmp tmp.fbs

The mutable API for struct s will have the following:

mutate_flag(value:boolean):boolean {
  this.bb!.writeInt8(this.bb_pos + 0, value);
  return true;
}

Which causes an error with TypeScript 5.9.2:

error TS2345: Argument of type 'boolean' is not assignable to parameter of type 'number'.
21   this.bb!.writeInt8(this.bb_pos + 0, value);
                                         ~~~~~

Equivalent generated API for table t does have the correct boolean-to-number conversion (using preceding +):

mutate_flag(value:boolean):boolean {
  const offset = this.bb!.__offset(this.bb_pos, 4);

  if (offset === 0) {
    return false;
  }

  this.bb!.writeInt8(this.bb_pos + offset, +value);
  return true;
}

[nurbo]

Looks like this special case:

flatbuffers/src/idl_gen_ts.cpp

Lines 1907 to 1909 in 067bfdb

	code +=
	" " + GenBBAccess() + write_method + "(this.bb_pos + offset, ";
	if (field.value.type.base_type == BASE_TYPE_BOOL) { code += "+"; }

should have been also applied the statement above:

flatbuffers/src/idl_gen_ts.cpp

Lines 1895 to 1898 in 067bfdb

	if (struct_def.fixed) {
	code += " " + GenBBAccess() + write_method + "(this.bb_pos + " +
	NumToString(field.value.offset) + ", ";
	} else {

Or rather outside of the conditional.