VHDL Issue Number:      1092
Classification:         Language Definition Problem
Language Version:       VHDL-93
Summary:                Must a selected name in a use clause denote anything?
Related Issues:         
Relevant LRM Sections:  10.4
Key Words and Phrases:  use clause, selected name, .all
Current Status:         Submitted
1076-1993 Disposition:  N/A
Disposition Rationale:  N/A
Superseded By:          N/A
-----------------------
Date Submitted:         1994/08/02
Author of Submission:   Daniel S. Barclay for Paul Graham
Author's Affiliation:   COMPASS Design Automation
Author's Post Address:  5457 Twin Knolls Rd., Suite 100
                        Columbia, MD  21045  USA
Author's Phone Number:  410-992-5700
Author's Fax Number:    410-992-3536
Author's Net Address:   daniel@compass-da.com
-----------------------
Date Analyzed:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.6 $
Date Last Revised:      $Date: 1995/05/15 20:07:17 $


Description of Problem
----------------------
It is not clear whether it is an error if the selected name in a use clause
does not denote any declarations.

For example, is the use clause in the following example legal?:

        package P1 is
            function f(a, b : INTEGER) return INTEGER;
        end;

        use WORK.Empty.g;
        entity User is
        end;

The second text paragraph in section 10.4 begins:

        Each selected name in a use clause identifies one or more declarations
        that will potentially become directly visible.

The wording "one or more" implies, though only weakly, that the name must 
denote something.

However, this implication would make the following code illegal:

        package Empty is
        end;

        use WORK.Empty.all;
        entity User is
        end;

Package Empty contains no declarations, so the selected name WORK.Empty.all 
identifies zero declarations (according to the third sentence in the paragraph
from section 10.4).  This example should not be illegal, so the above impli-
cation is inappropriate.

The next sentence says:

        If the suffix of the selected name is a simple name, character literal,
        or operator symbol, then the selected name identifies only the 
        declaration(s) of that simple name, character literal, or operator 
        symbol contained within the package or library denotes by the prefix 
        of the selected name.

Since this doesn't say "if any" near "declaration(s)", it is reasonable to
infer that it is an error if the name does not denote any declarations.
However, an explicit statement would be much clearer and more definite.


Proposed Resolution
-------------------
Correct the wording to cover the case of a selected name that has a suffix of 
"all" and that denotes zero declarations.

Especially because of that correction, specify that a selected name other than
one with a suffix of "all" must denote at least one declaration.


VASG-ISAC Analysis & Rationale
------------------------------
TBD


VASG-ISAC Recommendation for IEEE Std 1076-1993
-----------------------------------------------
TBD


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
TBD