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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- I T Y P E S --
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6 -- --
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7 -- S p e c --
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8 -- --
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9 -- Copyright (C) 1992-2010, Free Software Foundation, Inc. --
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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17 -- for more details. You should have received a copy of the GNU General --
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18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
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19 -- http://www.gnu.org/licenses for a complete copy of the license. --
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20 -- --
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21 -- GNAT was originally developed by the GNAT team at New York University. --
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22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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23 -- --
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24 ------------------------------------------------------------------------------
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25
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26 -- This package contains declarations for handling of implicit types
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27
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28 with Einfo; use Einfo;
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29 with Sem_Util; use Sem_Util;
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30 with Types; use Types;
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31
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32 package Itypes is
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33
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34 --------------------
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35 -- Implicit Types --
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36 --------------------
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37
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38 -- Implicit types (Itypes) are types and subtypes created by the semantic
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39 -- phase or the expander to reflect the underlying semantics. These could
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40 -- be generated by building trees for corresponding declarations and then
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41 -- analyzing these trees, but there are three reasons for not doing this
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42 -- in some cases:
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43
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44 -- 1. The declarations would require more tree nodes
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45
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46 -- 2. In some cases, the elaboration of these types is associated
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47 -- with internal nodes in the tree.
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48
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49 -- 3. For some types, notably class wide types, there is no Ada
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50 -- declaration that would correspond to the desired entity.
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51
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52 -- So instead, implicit types are constructed by simply creating an
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53 -- appropriate entity with the help of routines in this package. These
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54 -- entities are fully decorated, as described in Einfo (just as though
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55 -- they had been created by the normal analysis procedure).
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56
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57 -- The type declaration declaring an Itype must be analyzed with checks
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58 -- off because this declaration has not been inserted in the tree (if it
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59 -- has been then it is not an Itype), and hence checks that would be
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60 -- generated during the analysis cannot be inserted in the tree. At any
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61 -- rate, Itype analysis should always be done with checks off, otherwise
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62 -- duplicate checks will most likely be emitted.
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63
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64 -- Unlike types declared explicitly, implicit types are defined on first
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65 -- use, which means that Gigi detects the use of such types, and defines
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66 -- them at the point of the first use automatically.
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67
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68 -- Although Itypes are not explicitly declared, they are associated with
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69 -- a specific node in the tree (roughly the node that caused them to be
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70 -- created), via the Associated_Node_For_Itype field. This association is
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71 -- used particularly by New_Copy_Tree, which uses it to determine whether
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72 -- or not to copy a referenced Itype. If the associated node is part of
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73 -- the tree to be copied by New_Copy_Tree, then (since the idea of the
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74 -- call to New_Copy_Tree is to create a complete duplicate of a tree,
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75 -- as though it had appeared separately in the source), the Itype in
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76 -- question is duplicated as part of the New_Copy_Tree processing.
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77
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78 -- As a consequence of this copying mechanism, the association between
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79 -- Itypes and associated nodes must be one-to-one: several Itypes must
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80 -- not share an associated node. For example, the semantic decoration
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81 -- of an array aggregate generates several Itypes: for each index subtype
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82 -- and for the array subtype. The associated node of each index subtype
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83 -- is the corresponding range expression.
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84
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85 -- Notes on the use of the Parent field of an Itype
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86
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87 -- In some cases, we do create a declaration node for an itype, and in
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88 -- such cases, the Parent field of the Itype points to this declaration
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89 -- in the normal manner. This case can be detected by checking for a
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90 -- non-empty Parent field referencing a declaration whose Defining_Entity
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91 -- is the Itype in question.
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92
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93 -- In some other cases, where we don't generate such a declaration, as
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94 -- described above, the Itype is attached to the tree implicitly by being
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95 -- referenced elsewhere, e.g. as the Etype of some object. In this case
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96 -- the Parent field may be Empty.
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97
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98 -- In other cases where we don't generate a declaration for the Itype,
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99 -- the Itype may be attached to an arbitrary node in the tree, using
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100 -- the Parent field. This Parent field may even reference a declaration
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101 -- for a related different entity (hence the description of the tests
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102 -- needed for the case where a declaration for the Itype is created).
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103
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104 ------------------
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105 -- Create_Itype --
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106 ------------------
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107
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108 function Create_Itype
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109 (Ekind : Entity_Kind;
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110 Related_Nod : Node_Id;
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111 Related_Id : Entity_Id := Empty;
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112 Suffix : Character := ' ';
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113 Suffix_Index : Nat := 0;
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114 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
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115 -- Used to create a new Itype
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116 --
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117 -- Related_Nod is the node for which this Itype was created. It is
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118 -- set as the Associated_Node_For_Itype of the new Itype. The Sloc of
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119 -- the new Itype is that of this node.
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120 --
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121 -- Related_Id is present only if the implicit type name may be referenced
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122 -- as a public symbol, and thus needs a unique external name. The name
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123 -- is created by a call to:
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124 --
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125 -- New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T')
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126 --
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127 -- If the implicit type does not need an external name, then the
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128 -- Related_Id parameter is omitted (and hence Empty). In this case
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129 -- Suffix and Suffix_Index are ignored and the implicit type name is
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130 -- created by a call to Make_Temporary.
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131 --
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132 -- Note that in all cases, the name starts with "T". This is used
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133 -- to identify implicit types in the error message handling circuits.
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134 --
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135 -- The Scope_Id parameter specifies the scope of the created type, and
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136 -- is normally the Current_Scope as shown, but can be set otherwise.
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137 --
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138 -- The size/align fields are initialized to unknown (Uint_0).
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139 --
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140 -- If Ekind is in Access_Subprogram_Kind, Can_Use_Internal_Rep is set True,
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141 -- unless Always_Compatible_Rep_On_Target is True.
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142
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143 ---------------------------------
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144 -- Create_Null_Excluding_Itype --
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145 ---------------------------------
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146
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147 function Create_Null_Excluding_Itype
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148 (T : Entity_Id;
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149 Related_Nod : Node_Id;
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150 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
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151 -- Ada 2005 (AI-231): T is an access type and this subprogram creates and
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152 -- returns an internal access-subtype declaration of T that has the null
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153 -- exclusion attribute set to True.
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154 --
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155 -- Usage of null-excluding Itypes
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156 -- ------------------------------
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157 --
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158 -- type T1 is access ...
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159 -- type T2 is not null T1;
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160 --
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161 -- type Rec is record
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162 -- Comp : not null T1;
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163 -- end record;
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164 --
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165 -- type Arr is array (...) of not null T1;
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166 --
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167 -- Instead of associating the not-null attribute with the defining ids of
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168 -- these declarations, we generate an internal subtype declaration of T1
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169 -- that has the null exclusion attribute set to true.
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170
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171 end Itypes;
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