[Go] add typemaps for std::string*

Fixes #2214

CHANGES.current

@@ -7,6 +7,9 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2022-03-15: ianlancetaylor
+	    [Go] Add typemaps for std::string*.
+
 2022-03-15: ianlancetaylor
 	    [Go] Don't convert arrays to pointers if there is a "gotype"
 	    typemap entry.

Examples/test-suite/go_director_inout.i

@@ -120,15 +120,6 @@ type GoRetStruct struct {
     $1.assign(tmp->p, tmp->p + tmp->n);
 }
 
-%typemap(directorin) std::string * (_gostring_ temp) {
-    $input = &temp;
-    $input->p = (char *) $1->data();
-    $input->n = $1->size();
-}
-%typemap(directorargout) std::string * {
-    $1->assign($input->p, $input->p + $input->n);
-}
-
 %feature("director") MyClass;
 
 %inline

Lib/go/std_string.i

@@ -88,4 +88,54 @@ class string;
 %typemap(godirectorin,fragment="CopyString") const string &
 %{ $result = swigCopyString($input) %}
 
+
+%typemap(gotype) string * "*string"
+
+%typemap(in) string * (string temp)
+%{
+  temp.assign($input->p, $input->n);
+  $1 = &temp;
+%}
+
+%typemap(godirectorout) string *
+%{
+  {
+    p := Swig_malloc(len(*$input))
+    s := (*[1<<30]byte)(unsafe.Pointer(p))[:len(*$input)]
+    copy(s, *$input)
+    $result = (*string)(unsafe.Pointer(&s))
+  }
+%}
+
+%typemap(directorout) string * (string temp)
+%{
+  temp.assign($input->p, $input->n);
+  $result = &temp;
+  free($input.p);
+%}
+
+%typemap(out,fragment="AllocateString") string * (_gostring_ temp)
+%{
+  temp = Swig_AllocateString($1->data(), $1->length());
+  $result = &temp;
+%}
+
+%typemap(goout,fragment="CopyString") string *
+%{ *$result = swigCopyString(*$1) %}
+
+%typemap(directorin,fragment="AllocateString") string * (_gostring_ temp)
+%{
+  temp = Swig_AllocateString($1->data(), $1->length());
+  $input = &temp;
+%}
+
+%typemap(godirectorin,fragment="CopyString") string *
+%{ *$result = swigCopyString(*$input); %}
+
+%typemap(argout,fragment="AllocateString") string *
+%{ *$input = Swig_AllocateString($1->data(), $1->length()); %}
+
+%typemap(goargout,fragment="CopyString") string *
+%{ *$input = swigCopyString(*$1) %}
+
 }