Do no free external trailing text strings

See GenericMappingTools/pygmt#2524 for background.  Sees we are trying to free strings thar belong to Python and not GMT.  However, not solved yet.

src/gmt_api.c

@@ -4127,6 +4127,7 @@ GMT_LOCAL struct GMT_DATASET * gmtapi_import_dataset (struct GMTAPI_CTRL *API, i
 					S->data[col_pos_out] = V_obj->data[col_pos].f8;
 					SH->alloc_mode[col_pos_out] = GMT_ALLOC_EXTERNALLY;	/* Not this objects job to free what was passed in by reference */
 				}
+				SH->alloc_mode_text = GMT_ALLOC_EXTERNALLY; /* Not this object's job to free what was passed in by reference */
 				DH = gmt_get_DD_hidden (D_obj);
 				if (smode) S->text = V_obj->text;	/* Hook up trailing text array */
 				gmtapi_increment_d (D_obj, V_obj->n_rows, n_columns, 1U);	/* Update counters for D_obj with 1 segment */
@@ -4520,7 +4521,7 @@ GMT_LOCAL int gmtapi_export_dataset (struct GMTAPI_CTRL *API, int object_ID, uns
 				}
 				if (S->text) {
 					V_obj->text = S->text;
-					VH->alloc_mode_text = GMT_ALLOC_EXTERNALLY;	/* Since not duplicated, just pointed to */
+					VH->alloc_mode_text = SH->alloc_mode_text = GMT_ALLOC_EXTERNALLY;	/* Since not duplicated, just pointed to */
 				}
 				V_obj->n_rows = n_rows;
 				VH->alloc_level = S_obj->alloc_level;	/* Otherwise D_obj will be freed before we get to use data */

src/gmt_hidden.h

@@ -79,7 +79,8 @@ struct GMT_DATASEGMENT_HIDDEN {    /* Supporting information hidden from the API
 	double lat_limit;		/* For polar caps: the latitude of the point closest to the pole */
 	struct GMT_OGR_SEG *ogr;	/* NULL unless OGR/GMT metadata exist for this segment */
 	struct GMT_DATASEGMENT *next;	/* NULL unless polygon and has holes and pointing to next hole */
-	enum GMT_enum_alloc *alloc_mode;	/* Allocation mode per column [GMT_ALLOC_INTERNALLY] */
+	enum GMT_enum_alloc *alloc_mode;	/* Allocation mode per data column [GMT_ALLOC_INTERNALLY] */
+	enum GMT_enum_alloc alloc_mode_text;	/* Allocation mode for trailing text column [GMT_ALLOC_INTERNALLY] */
 	char *file[2];			/* Name of file or source [0 = in, 1 = out] */
 };
 

src/gmt_io.c

@@ -8795,13 +8795,15 @@ struct GMT_DATASET * gmt_transpose_dataset (struct GMT_CTRL *GMT, struct GMT_DAT
 	return (Dt);
 }
 
-GMT_LOCAL void gmtio_free_segment_text (struct GMT_CTRL *GMT, struct GMT_DATASEGMENT *S) {
-	/* Frees any array of trailing text items */
+GMT_LOCAL void gmtio_free_segment_text (struct GMT_CTRL *GMT, struct GMT_DATASEGMENT *S, struct GMT_DATASEGMENT_HIDDEN *SH) {
+	/* Frees any array of trailing text items unless externally allocated */
 	uint64_t row;
-	if (S->text == NULL) return;	/* No text */
-	for (row = 0; row < S->n_rows; row++)
-		gmt_M_str_free (S->text[row]);
-	gmt_M_free (GMT, S->text);
+	if (S->text == NULL) return;	/* No trailing text array */
+    if (SH->alloc_mode_text == GMT_ALLOC_INTERNALLY) {  /* We can free these strings */
+        for (row = 0; row < S->n_rows; row++)
+	       gmt_M_str_free (S->text[row]);
+    }
+	gmt_M_free (GMT, S->text); /* Always free the array holding the strings */
 }
 
 /*! . */
@@ -8825,7 +8827,7 @@ void gmt_free_segment (struct GMT_CTRL *GMT, struct GMT_DATASEGMENT **S) {
 	gmt_M_str_free ( segment->header);
 	for (k = 0; k < 2; k++) gmt_M_str_free (SH->file[k]);
 	if (SH->ogr) gmtio_free_ogr_seg (GMT, segment);	/* OGR metadata */
-	gmtio_free_segment_text (GMT, segment);
+	gmtio_free_segment_text (GMT, segment, SH);
 	gmt_M_free (GMT, SH->alloc_mode);
 	gmt_M_free (GMT, segment->hidden);
 	gmt_M_free (GMT, segment);