1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                             S E M _ W A R N                              --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1999-2011, 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 the routines used to deal with issuing warnings
27--  about uses of uninitialized variables and unused with's. It also has
28--  some unrelated routines related to the generation of warnings.
29
30with Alloc; use Alloc;
31with Table;
32with Types; use Types;
33
34package Sem_Warn is
35
36   ------------------------
37   -- Warnings Off Table --
38   ------------------------
39
40   type Warnings_Off_Entry is record
41      N : Node_Id;
42      --  A pragma Warnings (Off, ent) node
43
44      E : Entity_Id;
45      --  The entity involved
46   end record;
47
48   --  An entry is made in the following table for any valid Pragma Warnings
49   --  (Off, entity) encountered while Opt.Warn_On_Warnings_Off is True. It
50   --  is used to generate warnings on any of these pragmas that turn out not
51   --  to be needed, or that could be replaced by Unmodified/Unreferenced.
52
53   package Warnings_Off_Pragmas is new Table.Table (
54     Table_Component_Type => Warnings_Off_Entry,
55     Table_Index_Type     => Int,
56     Table_Low_Bound      => 0,
57     Table_Initial        => Alloc.Warnings_Off_Pragmas_Initial,
58     Table_Increment      => Alloc.Warnings_Off_Pragmas_Increment,
59     Table_Name           => "Name_Warnings_Off_Pragmas");
60
61   --------------------
62   -- Initialization --
63   --------------------
64
65   procedure Initialize;
66   --  Initialize this package for new compilation
67
68   ------------------------------------------
69   -- Routines to Handle Unused References --
70   ------------------------------------------
71
72   procedure Check_References (E : Entity_Id; Anod : Node_Id := Empty);
73   --  Called at the end of processing a declarative region. The entity E
74   --  is the entity for the scope. All entities declared in the region,
75   --  as indicated by First_Entity and the entity chain, are checked to
76   --  see if they are variables for which warnings need to be posted for
77   --  either no assignments, or a use before an assignment or no references
78   --  at all. The Anod node is present for the case of an accept statement,
79   --  and references the accept statement. This is used to place the warning
80   --  messages in the right place.
81
82   procedure Check_Unset_Reference (N : Node_Id);
83   --  N is the node for an expression which occurs in a reference position,
84   --  e.g. as the right side of an assignment. This procedure checks to see
85   --  if the node is a reference to a variable entity where the entity has
86   --  Not_Assigned set. If so, the Unset_Reference field is set if it is not
87   --  the first occurrence. No warning is posted, instead warnings will be
88   --  posted later by Check_References. The reason we do things that
89   --  way is that if there are no assignments anywhere, we prefer to flag
90   --  the entity, rather than a reference to it. Note that for the purposes
91   --  of this routine, a type conversion or qualified expression whose
92   --  expression is an entity is also processed. The reason that we do not
93   --  process these at the point of occurrence is that both these constructs
94   --  can occur in non-reference positions (e.g. as out parameters).
95
96   procedure Check_Unused_Withs (Spec_Unit : Unit_Number_Type := No_Unit);
97   --  This routine performs two kinds of checks. It checks that all with'ed
98   --  units are referenced, and that at least one entity of each with'ed
99   --  unit is referenced (the latter check catches units that are only
100   --  referenced in a use or package renaming statement). Appropriate
101   --  warning messages are generated if either of these situations is
102   --  detected.
103   --
104   --  A special case arises when a package body or a subprogram body with
105   --  a separate spec is being compiled. In this case, a with may appear
106   --  on the spec, but be needed only by the body. This still generates
107   --  a warning, but the text is different (the with is not redundant,
108   --  it is misplaced).
109   --
110   --  This special case is implemented by making an initial call to this
111   --  procedure with Spec_Unit set to the unit number of the separate spec.
112   --  This call does not generate any warning messages, but instead may
113   --  result in flags being set in the N_With_Clause node that record that
114   --  there was no use in the spec.
115   --
116   --  The main call (made after all units have been analyzed, with Spec_Unit
117   --  set to the default value of No_Unit) generates the required warnings
118   --  using the flags set by the initial call where appropriate to specialize
119   --  the text of the warning messages.
120
121   ---------------------
122   -- Output Routines --
123   ---------------------
124
125   procedure Output_Non_Modified_In_Out_Warnings;
126   --  Warnings about IN OUT parameters that could be IN are collected till
127   --  the end of the compilation process (see body of this routine for a
128   --  discussion of why this is done). This procedure outputs the warnings.
129   --  Note: this should be called before Output_Unreferenced_Messages, since
130   --  if we have an IN OUT warning, that's the one we want to see!
131
132   procedure Output_Obsolescent_Entity_Warnings (N : Node_Id; E : Entity_Id);
133   --  N is a reference to obsolescent entity E, for which appropriate warning
134   --  messages are to be generated (caller has already checked that warnings
135   --  are active and appropriate for this entity).
136
137   procedure Output_Unreferenced_Messages;
138   --  Warnings about unreferenced entities are collected till the end of
139   --  the compilation process (see Check_Unset_Reference for further
140   --  details). This procedure outputs waiting warnings, if any.
141
142   procedure Output_Unused_Warnings_Off_Warnings;
143   --  Warnings about pragma Warnings (Off, ent) statements that are unused,
144   --  or could be replaced by Unmodified/Unreferenced pragmas, are collected
145   --  till the end of the compilation process. This procedure outputs waiting
146   --  warnings if any.
147
148   ----------------------------
149   -- Other Warning Routines --
150   ----------------------------
151
152   procedure Check_Code_Statement (N : Node_Id);
153   --  Perform warning checks on a code statement node
154
155   procedure Check_Infinite_Loop_Warning (Loop_Statement : Node_Id);
156   --  N is the node for a loop statement. This procedure checks if a warning
157   --  for a possible infinite loop should be given for a suspicious WHILE or
158   --  EXIT WHEN condition.
159
160   procedure Check_Low_Bound_Tested (Expr : Node_Id);
161   --  Expr is the node for a comparison operation. This procedure checks if
162   --  the comparison is a source comparison of P'First with some other value
163   --  and if so, sets the Low_Bound_Tested flag on entity P to suppress
164   --  warnings about improper low bound assumptions (we assume that if the
165   --  code has a test that explicitly checks P'First, then it is not operating
166   --  in blind assumption mode).
167
168   procedure Warn_On_Known_Condition (C : Node_Id);
169   --  C is a node for a boolean expression resulting from a relational
170   --  or membership operation. If the expression has a compile time known
171   --  value, then a warning is output if all the following conditions hold:
172   --
173   --    1. Original expression comes from source. We don't want to generate
174   --       warnings for internally generated conditionals.
175   --
176   --    2. As noted above, the expression is a relational or membership
177   --       test, we don't want to generate warnings for boolean variables
178   --       since this is typical of conditional compilation in Ada.
179   --
180   --    3. The expression appears in a statement, rather than a declaration.
181   --       In practice, most occurrences in declarations are legitimate
182   --       conditionalizations, but occurrences in statements are often
183   --       errors for which the warning is useful.
184   --
185   --    4. The expression does not occur within an instantiation. A non-
186   --       static expression in a generic may become constant because of
187   --       the attributes of the actuals, and we do not want to warn on
188   --       these legitimate constant foldings.
189   --
190   --  If all these conditions are met, the warning is issued noting that
191   --  the result of the test is always false or always true as appropriate.
192
193   function Warn_On_Modified_As_Out_Parameter (E : Entity_Id) return Boolean;
194   --  Returns True if we should activate warnings for entity E being modified
195   --  as an out parameter. True if either Warn_On_Modified_Unread is set for
196   --  an only OUT parameter, or if Warn_On_All_Unread_Out_Parameters is set.
197
198   procedure Warn_On_Overlapping_Actuals (Subp : Entity_Id; N : Node_Id);
199   --  Called on a subprogram call. Checks whether an IN OUT actual that is
200   --  not by-copy may overlap with another actual, thus leading to aliasing
201   --  in the body of the called subprogram.
202
203   procedure Warn_On_Suspicious_Index (Name : Entity_Id; X : Node_Id);
204   --  This is called after resolving an indexed component or a slice. Name
205   --  is the entity for the name of the indexed array, and X is the subscript
206   --  for the indexed component case, or one of the bounds in the slice case.
207   --  If Name is an unconstrained parameter of a standard string type, and
208   --  the index is of the form of a literal or Name'Length [- literal], then
209   --  a warning is generated that the subscripting operation is possibly
210   --  incorrectly assuming a lower bound of 1.
211
212   procedure Warn_On_Unassigned_Out_Parameter
213     (Return_Node : Node_Id;
214      Scope_Id    : Entity_Id);
215   --  Called when processing a return statement given by Return_Node. Scope_Id
216   --  is the Entity_Id for the procedure in which the return statement lives.
217   --  A check is made for the case of a procedure with out parameters that
218   --  have not yet been assigned, and appropriate warnings are given.
219
220   procedure Warn_On_Useless_Assignment
221     (Ent : Entity_Id;
222      N   : Node_Id := Empty);
223   --  Called to check if we have a case of a useless assignment to the given
224   --  entity Ent, as indicated by a non-empty Last_Assignment field. This call
225   --  should only be made if at least one of the flags Warn_On_Modified_Unread
226   --  or Warn_On_All_Unread_Out_Parameters is True, and if Ent is in the
227   --  extended main source unit. N is Empty for the end of block call
228   --  (warning message says value unreferenced), or the it is the node for
229   --  an overwriting assignment (warning message points to this assignment).
230
231   procedure Warn_On_Useless_Assignments (E : Entity_Id);
232   pragma Inline (Warn_On_Useless_Assignments);
233   --  Called at the end of a block or subprogram. Scans the entities of the
234   --  block or subprogram to see if there are any variables for which useless
235   --  assignments were made (assignments whose values were never read).
236
237end Sem_Warn;
238