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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                             S E M _ W A R N                              --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1999-2010, Free Software Foundation, Inc.         --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT; see file COPYING3.  If not, go to --

-- http://www.gnu.org/licenses for a complete copy of the license.          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  This package contains the routines used to deal with issuing warnings

--  about uses of uninitialized variables and unused with's. It also has

--  some unrelated routines related to the generation of warnings.

with Alloc; use Alloc;

with Table;

with Types; use Types;

package Sem_Warn is

   ------------------------

   -- Warnings Off Table --

   ------------------------

   type Warnings_Off_Entry is record

      N : Node_Id;

      --  A pragma Warnings (Off, ent) node

      E : Entity_Id;

      --  The entity involved

   end record;

   --  An entry is made in the following table for any valid Pragma Warnings

   --  (Off, entity) encountered while Opt.Warn_On_Warnings_Off is True. It

   --  is used to generate warnings on any of these pragmas that turn out not

   --  to be needed, or that could be replaced by Unmodified/Unreferenced.

   package Warnings_Off_Pragmas is new Table.Table (

     Table_Component_Type => Warnings_Off_Entry,

     Table_Index_Type     => Int,

     Table_Low_Bound      => 0,

     Table_Initial        => Alloc.Warnings_Off_Pragmas_Initial,

     Table_Increment      => Alloc.Warnings_Off_Pragmas_Increment,

     Table_Name           => "Name_Warnings_Off_Pragmas");

   --------------------

   -- Initialization --

   --------------------

   procedure Initialize;

   --  Initialize this package for new compilation

   ------------------------------------------

   -- Routines to Handle Unused References --

   ------------------------------------------

   procedure Check_References (E : Entity_Id; Anod : Node_Id := Empty);

   --  Called at the end of processing a declarative region. The entity E

   --  is the entity for the scope. All entities declared in the region,

   --  as indicated by First_Entity and the entity chain, are checked to

   --  see if they are variables for which warnings need to be posted for

   --  either no assignments, or a use before an assignment or no references

   --  at all. The Anod node is present for the case of an accept statement,

   --  and references the accept statement. This is used to place the warning

   --  messages in the right place.

   procedure Check_Unset_Reference (N : Node_Id);

   --  N is the node for an expression which occurs in a reference position,

   --  e.g. as the right side of an assignment. This procedure checks to see

   --  if the node is a reference to a variable entity where the entity has

   --  Not_Assigned set. If so, the Unset_Reference field is set if it is not

   --  the first occurrence. No warning is posted, instead warnings will be

   --  posted later by Check_References. The reason we do things that

   --  way is that if there are no assignments anywhere, we prefer to flag

   --  the entity, rather than a reference to it. Note that for the purposes

   --  of this routine, a type conversion or qualified expression whose

   --  expression is an entity is also processed. The reason that we do not

   --  process these at the point of occurrence is that both these constructs

   --  can occur in non-reference positions (e.g. as out parameters).

   procedure Check_Unused_Withs (Spec_Unit : Unit_Number_Type := No_Unit);

   --  This routine performs two kinds of checks. It checks that all with'ed

   --  units are referenced, and that at least one entity of each with'ed

   --  unit is referenced (the latter check catches units that are only

   --  referenced in a use or package renaming statement). Appropriate

   --  warning messages are generated if either of these situations is

   --  detected.

   --

   --  A special case arises when a package body or a subprogram body with

   --  a separate spec is being compiled. In this case, a with may appear

   --  on the spec, but be needed only by the body. This still generates

   --  a warning, but the text is different (the with is not redundant,

   --  it is misplaced).

   --

   --  This special case is implemented by making an initial call to this

   --  procedure with Spec_Unit set to the unit number of the separate spec.

   --  This call does not generate any warning messages, but instead may

   --  result in flags being set in the N_With_Clause node that record that

   --  there was no use in the spec.

   --

   --  The main call (made after all units have been analyzed, with Spec_Unit

   --  set to the default value of No_Unit) generates the required warnings

   --  using the flags set by the initial call where appropriate to specialize

   --  the text of the warning messages.

   ---------------------

   -- Output Routines --

   ---------------------

   procedure Output_Non_Modified_In_Out_Warnings;

   --  Warnings about IN OUT parameters that could be IN are collected till

   --  the end of the compilation process (see body of this routine for a

   --  discussion of why this is done). This procedure outputs the warnings.

   --  Note: this should be called before Output_Unreferenced_Messages, since

   --  if we have an IN OUT warning, that's the one we want to see!

   procedure Output_Obsolescent_Entity_Warnings (N : Node_Id; E : Entity_Id);

   --  N is a reference to obsolescent entity E, for which appropriate warning

   --  messages are to be generated (caller has already checked that warnings

   --  are active and appropriate for this entity).

   procedure Output_Unreferenced_Messages;

   --  Warnings about unreferenced entities are collected till the end of

   --  the compilation process (see Check_Unset_Reference for further

   --  details). This procedure outputs waiting warnings, if any.

   procedure Output_Unused_Warnings_Off_Warnings;

   --  Warnings about pragma Warnings (Off, ent) statements that are unused,

   --  or could be replaced by Unmodified/Unreferenced pragmas, are collected

   --  till the end of the compilation process. This procedure outputs waiting

   --  warnings if any.

   ----------------------------

   -- Other Warning Routines --

   ----------------------------

   procedure Check_Code_Statement (N : Node_Id);

   --  Perform warning checks on a code statement node

   procedure Check_Infinite_Loop_Warning (Loop_Statement : Node_Id);

   --  N is the node for a loop statement. This procedure checks if a warning

   --  for a possible infinite loop should be given for a suspicious WHILE or

   --  EXIT WHEN condition.

   procedure Check_Low_Bound_Tested (Expr : Node_Id);

   --  Expr is the node for a comparison operation. This procedure checks if

   --  the comparison is a source comparison of P'First with some other value

   --  and if so, sets the Low_Bound_Tested flag on entity P to suppress

   --  warnings about improper low bound assumptions (we assume that if the

   --  code has a test that explicitly checks P'First, then it is not operating

   --  in blind assumption mode).

   procedure Warn_On_Known_Condition (C : Node_Id);

   --  C is a node for a boolean expression resulting from a relational

   --  or membership operation. If the expression has a compile time known

   --  value, then a warning is output if all the following conditions hold:

   --

   --    1. Original expression comes from source. We don't want to generate

   --       warnings for internally generated conditionals.

   --

   --    2. As noted above, the expression is a relational or membership

   --       test, we don't want to generate warnings for boolean variables

   --       since this is typical of conditional compilation in Ada.

   --

   --    3. The expression appears in a statement, rather than a declaration.

   --       In practice, most occurrences in declarations are legitimate

   --       conditionalizations, but occurrences in statements are often

   --       errors for which the warning is useful.

   --

   --    4. The expression does not occur within an instantiation. A non-

   --       static expression in a generic may become constant because of

   --       the attributes of the actuals, and we do not want to warn on

   --       these legitimate constant foldings.

   --

   --  If all these conditions are met, the warning is issued noting that

   --  the result of the test is always false or always true as appropriate.

   function Warn_On_Modified_As_Out_Parameter (E : Entity_Id) return Boolean;

   --  Returns True if we should activate warnings for entity E being modified

   --  as an out parameter. True if either Warn_On_Modified_Unread is set for

   --  an only OUT parameter, or if Warn_On_All_Unread_Out_Parameters is set.

   procedure Warn_On_Overlapping_Actuals (Subp : Entity_Id; N : Node_Id);

   --  Called on a subprogram call. Checks whether an IN OUT actual that is

   --  not by-copy may overlap with another actual, thus leading to aliasing

   --  in the body of the called subprogram.

   procedure Warn_On_Suspicious_Index (Name : Entity_Id; X : Node_Id);

   --  This is called after resolving an indexed component or a slice. Name

   --  is the entity for the name of the indexed array, and X is the subscript

   --  for the indexed component case, or one of the bounds in the slice case.

   --  If Name is an unconstrained parameter of a standard string type, and

   --  the index is of the form of a literal or Name'Length [- literal], then

   --  a warning is generated that the subscripting operation is possibly

   --  incorrectly assuming a lower bound of 1.

   procedure Warn_On_Unassigned_Out_Parameter

     (Return_Node : Node_Id;

      Scope_Id    : Entity_Id);

   --  Called when processing a return statement given by Return_Node. Scope_Id

   --  is the Entity_Id for the procedure in which the return statement lives.

   --  A check is made for the case of a procedure with out parameters that

   --  have not yet been assigned, and appropriate warnings are given.

   procedure Warn_On_Useless_Assignment

     (Ent : Entity_Id;

      N   : Node_Id := Empty);

   --  Called to check if we have a case of a useless assignment to the given

   --  entity Ent, as indicated by a non-empty Last_Assignment field. This call

   --  should only be made if at least one of the flags Warn_On_Modified_Unread

   --  or Warn_On_All_Unread_Out_Parameters is True, and if Ent is in the

   --  extended main source unit. N is Empty for the end of block call

   --  (warning message says value unreferenced), or the it is the node for

   --  an overwriting assignment (warning message points to this assignment).

   procedure Warn_On_Useless_Assignments (E : Entity_Id);

   pragma Inline (Warn_On_Useless_Assignments);

   --  Called at the end of a block or subprogram. Scans the entities of the

   --  block or subprogram to see if there are any variables for which useless

   --  assignments were made (assignments whose values were never read).

end Sem_Warn;