File : itypes.ads
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- I T Y P E S --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1992-2009, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
20 -- --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
23 -- --
24 ------------------------------------------------------------------------------
25
26 -- This package contains declarations for handling of implicit types
27
28 with Einfo; use Einfo;
29 with Sem_Util; use Sem_Util;
30 with Types; use Types;
31
32 package Itypes is
33
34 --------------------
35 -- Implicit Types --
36 --------------------
37
38 -- Implicit types (Itypes) are types and subtypes created by the semantic
39 -- phase or the expander to reflect the underlying semantics. These could
40 -- be generated by building trees for corresponding declarations and then
41 -- analyzing these trees, but there are three reasons for not doing this
42 -- in some cases:
43
44 -- 1. The declarations would require more tree nodes
45
46 -- 2. In some cases, the elaboration of these types is associated
47 -- with internal nodes in the tree.
48
49 -- 3. For some types, notably class wide types, there is no Ada
50 -- declaration that would correspond to the desired entity.
51
52 -- So instead, implicit types are constructed by simply creating an
53 -- appropriate entity with the help of routines in this package. These
54 -- entities are fully decorated, as described in Einfo (just as though
55 -- they had been created by the normal analysis procedure).
56
57 -- The type declaration declaring an Itype must be analyzed with checks
58 -- off because this declaration has not been inserted in the tree (if it
59 -- has been then it is not an Itype), and hence checks that would be
60 -- generated during the analysis cannot be inserted in the tree. At any
61 -- rate, Itype analysis should always be done with checks off, otherwise
62 -- duplicate checks will most likely be emitted.
63
64 -- Unlike types declared explicitly, implicit types are defined on first
65 -- use, which means that Gigi detects the use of such types, and defines
66 -- them at the point of the first use automatically.
67
68 -- Although Itypes are not explicitly declared, they are associated with
69 -- a specific node in the tree (roughly the node that caused them to be
70 -- created), via the Associated_Node_For_Itype field. This association is
71 -- used particularly by New_Copy_Tree, which uses it to determine whether
72 -- or not to copy a referenced Itype. If the associated node is part of
73 -- the tree to be copied by New_Copy_Tree, then (since the idea of the
74 -- call to New_Copy_Tree is to create a complete duplicate of a tree,
75 -- as though it had appeared separately in the source), the Itype in
76 -- question is duplicated as part of the New_Copy_Tree processing.
77
78 -- As a consequence of this copying mechanism, the association between
79 -- Itypes and associated nodes must be one-to-one: several Itypes must
80 -- not share an associated node. For example, the semantic decoration
81 -- of an array aggregate generates several Itypes: for each index subtype
82 -- and for the array subtype. The associated node of each index subtype
83 -- is the corresponding range expression.
84
85 -- Notes on the use of the Parent field of an Itype
86
87 -- In some cases, we do create a declaration node for an itype, and in
88 -- such cases, the Parent field of the Itype points to this declaration
89 -- in the normal manner. This case can be detected by checking for a
90 -- non-empty Parent field referencing a declaration whose Defining_Entity
91 -- is the Itype in question.
92
93 -- In some other cases, where we don't generate such a declaration, as
94 -- described above, the Itype is attached to the tree implicitly by being
95 -- referenced elsewhere, e.g. as the Etype of some object. In this case
96 -- the Parent field may be Empty.
97
98 -- In other cases where we don't generate a declaration for the Itype,
99 -- the Itype may be attached to an arbitrary node in the tree, using
100 -- the Parent field. This Parent field may even reference a declaration
101 -- for a related different entity (hence the description of the tests
102 -- needed for the case where a declaration for the Itype is created).
103
104 ------------------
105 -- Create_Itype --
106 ------------------
107
108 function Create_Itype
109 (Ekind : Entity_Kind;
110 Related_Nod : Node_Id;
111 Related_Id : Entity_Id := Empty;
112 Suffix : Character := ' ';
113 Suffix_Index : Nat := 0;
114 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
115 -- Used to create a new Itype
116 --
117 -- Related_Nod is the node for which this Itype was created. It is
118 -- set as the Associated_Node_For_Itype of the new Itype. The Sloc of
119 -- the new Itype is that of this node.
120 --
121 -- Related_Id is present only if the implicit type name may be referenced
122 -- as a public symbol, and thus needs a unique external name. The name
123 -- is created by a call to:
124 --
125 -- New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T')
126 --
127 -- If the implicit type does not need an external name, then the
128 -- Related_Id parameter is omitted (and hence Empty). In this case
129 -- Suffix and Suffix_Index are ignored and the implicit type name is
130 -- created by a call to Make_Temporary.
131 --
132 -- Note that in all cases, the name starts with "T". This is used
133 -- to identify implicit types in the error message handling circuits.
134 --
135 -- The Scope_Id parameter specifies the scope of the created type, and
136 -- is normally the Current_Scope as shown, but can be set otherwise.
137 --
138 -- The size/align fields are initialized to unknown (Uint_0).
139 --
140 -- If Ekind is in Access_Subprogram_Kind, Can_Use_Internal_Rep is set True,
141 -- unless Always_Compatible_Rep_On_Target is True.
142
143 ---------------------------------
144 -- Create_Null_Excluding_Itype --
145 ---------------------------------
146
147 function Create_Null_Excluding_Itype
148 (T : Entity_Id;
149 Related_Nod : Node_Id;
150 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
151 -- Ada 2005 (AI-231): T is an access type and this subprogram creates and
152 -- returns an internal access-subtype declaration of T that has the null
153 -- exclusion attribute set to True.
154 --
155 -- Usage of null-excluding Itypes
156 -- ------------------------------
157 --
158 -- type T1 is access ...
159 -- type T2 is not null T1;
160 --
161 -- type Rec is record
162 -- Comp : not null T1;
163 -- end record;
164 --
165 -- type Arr is array (...) of not null T1;
166 --
167 -- Instead of associating the not-null attribute with the defining ids of
168 -- these declarations, we generate an internal subtype declaration of T1
169 -- that has the null exclusion attribute set to true.
170
171 end Itypes;