HL: address PR HDFGroup#6140 review comments

H5LT.c:
- Push H5E_NOSPACE on strdup OOM in H5LTtext_to_dtype so the HDF5
  error stack is populated on allocation failure
- Rename static helper H5LT_append_dtype_super_text -> append_dtype_super_text
  to match the TU-local naming convention (no H5LT_ prefix for file-static
  helpers); update all four call sites
- Add comment on super_len == 0 guard explaining calloc(0,...) avoidance
- Push H5E_NOSPACE from calloc failure inside the helper

H5TB.c (H5TBget_field_info):
- Clarify else-branch comment: the two-branch structure is an efficiency
  optimization (copy only name_len+1 bytes rather than HLTB_MAX_FIELD_LEN-1),
  not a backward-compatibility concern (addresses jhendersonHDF review note)

Author: brtnfld

hl/src/H5LT.c

@@ -1889,8 +1889,9 @@ H5LTtext_to_dtype(const char *text, H5LT_lang_t lang_type)
 
     input_len = strlen(text);
     myinput   = strdup(text);
-    if (!myinput)
-        goto out;
+    if (!myinput) {
+        H5Epush_ret(__func__, H5E_ERR_CLS, H5E_RESOURCE, H5E_NOSPACE, "memory allocation failed", -1);
+    }
 
     if ((type_id = H5LTyyparse()) < 0) {
         free(myinput);
@@ -2189,7 +2190,7 @@ H5LTdtype_to_text(hid_t dtype, char *str, H5LT_lang_t lang_type, size_t *len)
 }
 
 /*-------------------------------------------------------------------------
- * Function:    H5LT_append_dtype_super_text
+ * Function:    append_dtype_super_text
  *
  * Purpose:     Helper function to get super type text and append it to dt_str.
  *              This encapsulates the common pattern of: allocate buffer,
@@ -2200,21 +2201,23 @@ H5LTdtype_to_text(hid_t dtype, char *str, H5LT_lang_t lang_type, size_t *len)
  *-------------------------------------------------------------------------
  */
 static char *
-H5LT_append_dtype_super_text(hid_t super, char *dt_str, H5LT_lang_t lang, size_t *slen, bool no_user_buf)
+append_dtype_super_text(hid_t super, char *dt_str, H5LT_lang_t lang, size_t *slen, bool no_user_buf)
 {
     size_t super_len;
     char  *stmp = NULL;
 
     /* Get required buffer size for super type text */
     if (H5LTdtype_to_text(super, NULL, lang, &super_len) < 0)
         return NULL;
+    /* Treat zero-length result as failure rather than calling calloc(0,...) */
     if (super_len == 0)
         return NULL;
 
     /* Allocate buffer for super type text */
     stmp = (char *)calloc(super_len, sizeof(char));
-    if (!stmp)
-        return NULL;
+    if (!stmp) {
+        H5Epush_ret(__func__, H5E_ERR_CLS, H5E_RESOURCE, H5E_NOSPACE, "memory allocation failed", NULL);
+    }
 
     /* Convert super type to text */
     if (H5LTdtype_to_text(super, stmp, lang, &super_len) < 0) {
@@ -2634,7 +2637,7 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
             if ((super = H5Tget_super(dtype)) < 0)
                 goto out;
             {
-                char *tmp = H5LT_append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
+                char *tmp = append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
                 H5Tclose(super);
                 if (!tmp) {
                     dt_str = NULL; /* freed by callee's realloc_and_append on failure */
@@ -2673,7 +2676,7 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
             if ((super = H5Tget_super(dtype)) < 0)
                 goto out;
             {
-                char *tmp = H5LT_append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
+                char *tmp = append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
                 H5Tclose(super);
                 if (!tmp) {
                     dt_str = NULL; /* freed by callee's realloc_and_append on failure */
@@ -2727,7 +2730,7 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
             if ((super = H5Tget_super(dtype)) < 0)
                 goto out;
             {
-                char *tmp = H5LT_append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
+                char *tmp = append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
                 H5Tclose(super);
                 if (!tmp) {
                     dt_str = NULL; /* freed by callee's realloc_and_append on failure */
@@ -2832,7 +2835,7 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
             if ((super = H5Tget_super(dtype)) < 0)
                 goto out;
             {
-                char *tmp = H5LT_append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
+                char *tmp = append_dtype_super_text(super, dt_str, lang, slen, no_user_buf);
                 H5Tclose(super);
                 if (!tmp) {
                     dt_str = NULL; /* freed by callee's realloc_and_append on failure */

hl/src/H5TB.c

@@ -3038,8 +3038,9 @@ H5TBget_field_info(hid_t loc_id, const char *dset_name, char *field_names[], siz
                 field_names[i][HLTB_MAX_FIELD_LEN - 1] = '\0';
             }
             else {
-                /* name_len < HLTB_MAX_FIELD_LEN, so name_len + 1 <= HLTB_MAX_FIELD_LEN.
-                 * Callers must provide buffers of at least HLTB_MAX_FIELD_LEN bytes each
+                /* name fits within the limit: copy only name_len + 1 bytes (more efficient
+                 * than copying HLTB_MAX_FIELD_LEN - 1 bytes).  name_len + 1 <= HLTB_MAX_FIELD_LEN,
+                 * and callers must provide buffers of at least HLTB_MAX_FIELD_LEN bytes each
                  * (documented in H5TBpublic.h), so this copy is within bounds. */
                 memcpy(field_names[i], member_name, name_len + 1);
             }