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

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                                  S E M                                   --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1992-2009, 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.      --

--                                                                          --

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

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

-- Semantic Analysis: General Model --

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

--  Semantic processing involves 3 phases which are highly intertwined

--  (i.e. mutually recursive):

--    Analysis     implements the bulk of semantic analysis such as

--                 name analysis and type resolution for declarations,

--                 instructions and expressions.  The main routine

--                 driving this process is procedure Analyze given below.

--                 This analysis phase is really a bottom up pass that is

--                 achieved during the recursive traversal performed by the

--                 Analyze_... procedures implemented in the sem_* packages.

--                 For expressions this phase determines unambiguous types

--                 and collects sets of possible types where the

--                 interpretation is potentially ambiguous.

--    Resolution   is carried out only for expressions to finish type

--                 resolution that was initiated but not necessarily

--                 completed during analysis (because of overloading

--                 ambiguities). Specifically, after completing the bottom

--                 up pass carried out during analysis for expressions, the

--                 Resolve routine (see the spec of sem_res for more info)

--                 is called to perform a top down resolution with

--                 recursive calls to itself to resolve operands.

--    Expansion    if we are not generating code this phase is a no-op.

--                 otherwise this phase expands, i.e. transforms, original

--                 declaration, expressions or instructions into simpler

--                 structures that can be handled by the back-end. This

--                 phase is also in charge of generating code which is

--                 implicit in the original source (for instance for

--                 default initializations, controlled types, etc.)

--                 There are two separate instances where expansion is

--                 invoked. For declarations and instructions, expansion is

--                 invoked just after analysis since no resolution needs

--                 to be performed. For expressions, expansion is done just

--                 after resolution. In both cases expansion is done from the

--                 bottom up just before the end of Analyze for instructions

--                 and declarations or the call to Resolve for expressions.

--                 The main routine driving expansion is Expand.

--                 See the spec of Expander for more details.

--  To summarize, in normal code generation mode we recursively traverse the

--  abstract syntax tree top-down performing semantic analysis bottom

--  up. For instructions and declarations, before the call to the Analyze

--  routine completes we perform expansion since at that point we have all

--  semantic information needed. For expression nodes, after the call to

--  Analysis terminates we invoke the Resolve routine to transmit top-down

--  the type that was gathered by Analyze which will resolve possible

--  ambiguities in the expression. Just before the call to Resolve

--  terminates, the expression can be expanded since all the semantic

--  information is available at that point.

--  If we are not generating code then the expansion phase is a no-op

--  When generating code there are a number of exceptions to the basic

--  Analysis-Resolution-Expansion model for expressions. The most prominent

--  examples are the handling of default expressions and aggregates.

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

-- Handling of Default and Per-Object Expressions (Spec-Expressions) --

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

--  The default expressions in component declarations and in procedure

--  specifications (but not the ones in object declarations) are quite tricky

--  to handle. The problem is that some processing is required at the point

--  where the expression appears:

--    visibility analysis (including user defined operators)

--    freezing of static expressions

--  but other processing must be deferred until the enclosing entity (record or

--  procedure specification) is frozen:

--    freezing of any other types in the expression expansion

--    generation of code

--  A similar situation occurs with the argument of priority and interrupt

--  priority pragmas that appear in task and protected definition specs and

--  other cases of per-object expressions (see RM 3.8(18)).

--  Another similar case is the conditions in precondition and postcondition

--  pragmas that appear with subprogram specifications rather than in the body.

--  Collectively we call these Spec_Expressions. The routine that performs the

--  special analysis is called Analyze_Spec_Expression.

--  Expansion has to be deferred since you can't generate code for expressions

--  that reference types that have not been frozen yet. As an example, consider

--  the following:

--      type x is delta 0.5 range -10.0 .. +10.0;

--      ...

--      type q is record

--        xx : x := y * z;

--      end record;

--      for x'small use 0.25

--  The expander is in charge of dealing with fixed-point, and of course the

--  small declaration, which is not too late, since the declaration of type q

--  does *not* freeze type x, definitely affects the expanded code.

--  Another reason that we cannot expand early is that expansion can generate

--  range checks. These range checks need to be inserted not at the point of

--  definition but at the point of use. The whole point here is that the value

--  of the expression cannot be obtained at the point of declaration, only at

--  the point of use.

--  Generally our model is to combine analysis resolution and expansion, but

--  this is the one case where this model falls down. Here is how we patch

--  it up without causing too much distortion to our basic model.

--  A switch (In_Spec_Expression) is set to show that we are in the initial

--  occurrence of a default expression. The analyzer is then called on this

--  expression with the switch set true. Analysis and resolution proceed almost

--  as usual, except that Freeze_Expression will not freeze non-static

--  expressions if this switch is set, and the call to Expand at the end of

--  resolution is skipped. This also skips the code that normally sets the

--  Analyzed flag to True. The result is that when we are done the tree is

--  still marked as unanalyzed, but all types for static expressions are frozen

--  as required, and all entities of variables have been recorded. We then turn

--  off the switch, and later on reanalyze the expression with the switch off.

--  The effect is that this second analysis freezes the rest of the types as

--  required, and generates code but visibility analysis is not repeated since

--  all the entities are marked.

--  The second analysis (the one that generates code) is in the context

--  where the code is required. For a record field default, this is in the

--  initialization procedure for the record and for a subprogram default

--  parameter, it is at the point the subprogram is frozen. For a priority or

--  storage size pragma it is in the context of the Init_Proc for the task or

--  protected object. For a pre/postcondition pragma it is in the body when

--  code for the pragma is generated.

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

-- Pre-Analysis --

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

--  For certain kind of expressions, such as aggregates, we need to defer

--  expansion of the aggregate and its inner expressions after the whole

--  set of expressions appearing inside the aggregate have been analyzed.

--  Consider, for instance the following example:

--

--     (1 .. 100 => new Thing (Function_Call))

--

--  The normal Analysis-Resolution-Expansion mechanism where expansion of the

--  children is performed before expansion of the parent does not work if the

--  code generated for the children by the expander needs to be evaluated

--  repeatedly (for instance in the above aggregate "new Thing (Function_Call)"

--  needs to be called 100 times.)

--  The reason why this mechanism does not work is that, the expanded code for

--  the children is typically inserted above the parent and thus when the

--  father gets expanded no re-evaluation takes place. For instance in the case

--  of aggregates if "new Thing (Function_Call)" is expanded before of the

--  aggregate the expanded code will be placed outside of the aggregate and

--  when expanding the aggregate the loop from 1 to 100 will not surround the

--  expanded code for "new Thing (Function_Call)".

--  To remedy this situation we introduce a new flag which signals whether we

--  want a full analysis (i.e. expansion is enabled) or a pre-analysis which

--  performs Analysis and Resolution but no expansion.

--  After the complete pre-analysis of an expression has been carried out we

--  can transform the expression and then carry out the full three stage

--  (Analyze-Resolve-Expand) cycle on the transformed expression top-down so

--  that the expansion of inner expressions happens inside the newly generated

--  node for the parent expression.

--  Note that the difference between processing of default expressions and

--  pre-analysis of other expressions is that we do carry out freezing in

--  the latter but not in the former (except for static scalar expressions).

--  The routine that performs preanalysis and corresponding resolution is

--  called Preanalyze_And_Resolve and is in Sem_Res.

with Alloc;

with Einfo;  use Einfo;

with Opt;    use Opt;

with Table;

with Types;  use Types;

package Sem is

   New_Nodes_OK : Int := 1;

   --  Temporary flag for use in checking out HLO. Set non-zero if it is

   --  OK to generate new nodes.

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

   -- Semantic Analysis Flags --

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

   Full_Analysis : Boolean := True;

   --  Switch to indicate if we are doing a full analysis or a pre-analysis.

   --  In normal analysis mode (Analysis-Expansion for instructions or

   --  declarations) or (Analysis-Resolution-Expansion for expressions) this

   --  flag is set. Note that if we are not generating code the expansion phase

   --  merely sets the Analyzed flag to True in this case. If we are in

   --  Pre-Analysis mode (see above) this flag is set to False then the

   --  expansion phase is skipped.

   --

   --  When this flag is False the flag Expander_Active is also False (the

   --  Expander_Active flag defined in the spec of package Expander tells you

   --  whether expansion is currently enabled). You should really regard this

   --  as a read only flag.

   In_Spec_Expression : Boolean := False;

   --  Switch to indicate that we are in a spec-expression, as described

   --  above. Note that this must be recursively saved on a Semantics call

   --  since it is possible for the analysis of an expression to result in a

   --  recursive call (e.g. to get the entity for System.Address as part of the

   --  processing of an Address attribute reference). When this switch is True

   --  then Full_Analysis above must be False. You should really regard this as

   --  a read only flag.

   In_Deleted_Code : Boolean := False;

   --  If the condition in an if-statement is statically known, the branch

   --  that is not taken is analyzed with expansion disabled, and the tree

   --  is deleted after analysis. Itypes generated in deleted code must be

   --  frozen from start, because the tree on which they depend will not

   --  be available at the freeze point.

   In_Inlined_Body : Boolean := False;

   --  Switch to indicate that we are analyzing and resolving an inlined body.

   --  Type checking is disabled in this context, because types are known to be

   --  compatible. This avoids problems with private types whose full view is

   --  derived from private types.

   Inside_A_Generic : Boolean := False;

   --  This flag is set if we are processing a generic specification, generic

   --  definition, or generic body. When this flag is True the Expander_Active

   --  flag is False to disable any code expansion (see package Expander). Only

   --  the generic processing can modify the status of this flag, any other

   --  client should regard it as read-only.

   --  Probably should be called Inside_A_Generic_Template ???

   Inside_Freezing_Actions : Nat := 0;

   --  Flag indicating whether we are within a call to Expand_N_Freeze_Actions.

   --  Non-zero means we are inside (it is actually a level counter to deal

   --  with nested calls). Used to avoid traversing the tree each time a

   --  subprogram call is processed to know if we must not clear all constant

   --  indications from entities in the current scope. Only the expansion of

   --  freezing nodes can modify the status of this flag, any other client

   --  should regard it as read-only.

   Unloaded_Subunits : Boolean := False;

   --  This flag is set True if we have subunits that are not loaded. This

   --  occurs when the main unit is a subunit, and contains lower level

   --  subunits that are not loaded. We use this flag to suppress warnings

   --  about unused variables, since these warnings are unreliable in this

   --  case. We could perhaps do a more accurate job and retain some of the

   --  warnings, but it is quite a tricky job.

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

   -- Handling of Check Suppression --

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

   --  There are two kinds of suppress checks: scope based suppress checks,

   --  and entity based suppress checks.

   --  Scope based suppress checks for the predefined checks (from initial

   --  command line arguments, or from Suppress pragmas not including an entity

   --  entity name) are recorded in the Sem.Suppress variable, and all that is

   --  necessary is to save the state of this variable on scope entry, and

   --  restore it on scope exit. This mechanism allows for fast checking of

   --  the scope suppress state without needing complex data structures.

   --  Entity based checks, from Suppress/Unsuppress pragmas giving an

   --  Entity_Id and scope based checks for non-predefined checks (introduced

   --  using pragma Check_Name), are handled as follows. If a suppress or

   --  unsuppress pragma is encountered for a given entity, then the flag

   --  Checks_May_Be_Suppressed is set in the entity and an entry is made in

   --  either the Local_Entity_Suppress stack (case of pragma that appears in

   --  other than a package spec), or in the Global_Entity_Suppress stack (case

   --  of pragma that appears in a package spec, which is by the rule of RM

   --  11.5(7) applicable throughout the life of the entity). Similarly, a

   --  Suppress/Unsuppress pragma for a non-predefined check which does not

   --  specify an entity is also stored in one of these stacks.

   --  If the Checks_May_Be_Suppressed flag is set in an entity then the

   --  procedure is to search first the local and then the global suppress

   --  stacks (we search these in reverse order, top element first). The only

   --  other point is that we have to make sure that we have proper nested

   --  interaction between such specific pragmas and locally applied general

   --  pragmas applying to all entities. This is achieved by including in the

   --  Local_Entity_Suppress table dummy entries with an empty Entity field

   --  that are applicable to all entities. A similar search is needed for any

   --  non-predefined check even if no specific entity is involved.

   Scope_Suppress : Suppress_Array := Suppress_Options;

   --  This array contains the current scope based settings of the suppress

   --  switches. It is initialized from the options as shown, and then modified

   --  by pragma Suppress. On entry to each scope, the current setting is saved

   --  the scope stack, and then restored on exit from the scope. This record

   --  may be rapidly checked to determine the current status of a check if

   --  no specific entity is involved or if the specific entity involved is

   --  one for which no specific Suppress/Unsuppress pragma has been set (as

   --  indicated by the Checks_May_Be_Suppressed flag being set).

   --  This scheme is a little complex, but serves the purpose of enabling

   --  a very rapid check in the common case where no entity specific pragma

   --  applies, and gives the right result when such pragmas are used even

   --  in complex cases of nested Suppress and Unsuppress pragmas.

   --  The Local_Entity_Suppress and Global_Entity_Suppress stacks are handled

   --  using dynamic allocation and linked lists. We do not often use this

   --  approach in the compiler (preferring to use extensible tables instead).

   --  The reason we do it here is that scope stack entries save a pointer to

   --  the current local stack top, which is also saved and restored on scope

   --  exit. Furthermore for processing of generics we save pointers to the

   --  top of the stack, so that the local stack is actually a tree of stacks

   --  rather than a single stack, a structure that is easy to represent using

   --  linked lists, but impossible to represent using a single table. Note

   --  that because of the generic issue, we never release entries in these

   --  stacks, but that's no big deal, since we are unlikely to have a huge

   --  number of Suppress/Unsuppress entries in a single compilation.

   type Suppress_Stack_Entry;

   type Suppress_Stack_Entry_Ptr is access all Suppress_Stack_Entry;

   type Suppress_Stack_Entry is record

      Entity : Entity_Id;

      --  Entity to which the check applies, or Empty for a check that has

      --  no entity name (and thus applies to all entities).

      Check : Check_Id;

      --  Check which is set (can be All_Checks for the All_Checks case)

      Suppress : Boolean;

      --  Set True for Suppress, and False for Unsuppress

      Prev : Suppress_Stack_Entry_Ptr;

      --  Pointer to previous entry on stack

      Next : Suppress_Stack_Entry_Ptr;

      --  All allocated Suppress_Stack_Entry records are chained together in

      --  a linked list whose head is Suppress_Stack_Entries, and the Next

      --  field is used as a forward pointer (null ends the list). This is

      --  used to free all entries in Sem.Init (which will be important if

      --  we ever setup the compiler to be reused).

   end record;

   Suppress_Stack_Entries : Suppress_Stack_Entry_Ptr := null;

   --  Pointer to linked list of records (see comments for Next above)

   Local_Suppress_Stack_Top : Suppress_Stack_Entry_Ptr;

   --  Pointer to top element of local suppress stack. This is the entry that

   --  is saved and restored in the scope stack, and also saved for generic

   --  body expansion.

   Global_Suppress_Stack_Top : Suppress_Stack_Entry_Ptr;

   --  Pointer to top element of global suppress stack

   procedure Push_Local_Suppress_Stack_Entry

     (Entity   : Entity_Id;

      Check    : Check_Id;

      Suppress : Boolean);

   --  Push a new entry on to the top of the local suppress stack, updating

   --  the value in Local_Suppress_Stack_Top;

   procedure Push_Global_Suppress_Stack_Entry

     (Entity   : Entity_Id;

      Check    : Check_Id;

      Suppress : Boolean);

   --  Push a new entry on to the top of the global suppress stack, updating

   --  the value in Global_Suppress_Stack_Top;

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

   -- Scope Stack --

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

   --  The scope stack indicates the declarative regions that are currently

   --  being processed (analyzed and/or expanded). The scope stack is one of

   --  the basic visibility structures in the compiler: entities that are

   --  declared in a scope that is currently on the scope stack are immediately

   --  visible (leaving aside issues of hiding and overloading).

   --  Initially, the scope stack only contains an entry for package Standard.

   --  When a compilation unit, subprogram unit, block or declarative region

   --  is being processed, the corresponding entity is pushed on the scope

   --  stack. It is removed after the processing step is completed. A given

   --  entity can be placed several times on the scope stack, for example

   --  when processing derived type declarations, freeze nodes, etc. The top

   --  of the scope stack is the innermost scope currently being processed.

   --  It is obtained through function Current_Scope. After a compilation unit

   --  has been processed, the scope stack must contain only Standard.

   --  The predicate In_Open_Scopes specifies whether a scope is currently

   --  on the scope stack.

   --  This model is complicated by the need to compile units on the fly, in

   --  the middle of the compilation of other units. This arises when compiling

   --  instantiations, and when compiling run-time packages obtained through

   --  rtsfind. Given that the scope stack is a single static and global

   --  structure (not originally designed for the recursive processing required

   --  by rtsfind for example) additional machinery is needed to indicate what

   --  is currently being compiled. As a result, the scope stack holds several

   --  contiguous sections that correspond to the compilation of a given

   --  compilation unit. These sections are separated by distinct occurrences

   --  of package Standard. The currently active section of the scope stack

   --  goes from the current scope to the first (innermost) occurrence of

   --  Standard, which is additionally marked with the flag

   --  Is_Active_Stack_Base. The basic visibility routine (Find_Direct_Name, in

   --  Sem_Ch8) uses this contiguous section of the scope stack to determine

   --  whether a given entity is or is not visible at a point. In_Open_Scopes

   --  only examines the currently active section of the scope stack.

   --  Similar complications arise when processing child instances. These

   --  must be compiled in the context of parent instances, and therefore the

   --  parents must be pushed on the stack before compiling the child, and

   --  removed afterwards. Routines Save_Scope_Stack and Restore_Scope_Stack

   --  are used to set/reset the visibility of entities declared in scopes

   --  that are currently on the scope stack, and are used when compiling

   --  instance bodies on the fly.

   --  It is clear in retrospect that all semantic processing and visibility

   --  structures should have been fully recursive. The rtsfind mechanism,

   --  and the complexities brought about by subunits and by generic child

   --  units and their instantiations, have led to a hybrid model that carries

   --  more state than one would wish.

   type Scope_Stack_Entry is record

      Entity : Entity_Id;

      --  Entity representing the scope

      Last_Subprogram_Name : String_Ptr;

      --  Pointer to name of last subprogram body in this scope. Used for

      --  testing proper alpha ordering of subprogram bodies in scope.

      Save_Scope_Suppress  : Suppress_Array;

      --  Save contents of Scope_Suppress on entry

      Save_Local_Suppress_Stack_Top : Suppress_Stack_Entry_Ptr;

      --  Save contents of Local_Suppress_Stack on entry to restore on exit

      Save_Check_Policy_List : Node_Id;

      --  Save contents of Check_Policy_List on entry to restore on exit

      Is_Transient : Boolean;

      --  Marks transient scopes (see Exp_Ch7 body for details)

      Previous_Visibility : Boolean;

      --  Used when installing the parent(s) of the current compilation unit.

      --  The parent may already be visible because of an ongoing compilation,

      --  and the proper visibility must be restored on exit. The flag is

      --  typically needed when the context of a child unit requires

      --  compilation of a sibling. In other cases the flag is set to False.

      --  See Sem_Ch10 (Install_Parents, Remove_Parents).

      Node_To_Be_Wrapped : Node_Id;

      --  Only used in transient scopes. Records the node which will

      --  be wrapped by the transient block.

      Actions_To_Be_Wrapped_Before : List_Id;

      Actions_To_Be_Wrapped_After  : List_Id;

      --  Actions that have to be inserted at the start or at the end of a

      --  transient block. Used to temporarily hold these actions until the

      --  block is created, at which time the actions are moved to the block.

      Pending_Freeze_Actions : List_Id;

      --  Used to collect freeze entity nodes and associated actions that are

      --  generated in an inner context but need to be analyzed outside, such

      --  as records and initialization procedures. On exit from the scope,

      --  this list of actions is inserted before the scope construct and

      --  analyzed to generate the corresponding freeze processing and

      --  elaboration of other associated actions.

      First_Use_Clause : Node_Id;

      --  Head of list of Use_Clauses in current scope. The list is built when

      --  the declarations in the scope are processed. The list is traversed

      --  on scope exit to undo the effect of the use clauses.

      Component_Alignment_Default : Component_Alignment_Kind;

      --  Component alignment to be applied to any record or array types that

      --  are declared for which a specific component alignment pragma does not

      --  set the alignment.

      Is_Active_Stack_Base : Boolean;

      --  Set to true only when entering the scope for Standard_Standard from

      --  from within procedure Semantics. Indicates the base of the current

      --  active set of scopes. Needed by In_Open_Scopes to handle cases where

      --  Standard_Standard can be pushed anew on the scope stack to start a

      --  new active section (see comment above).

   end record;

   package Scope_Stack is new Table.Table (

     Table_Component_Type => Scope_Stack_Entry,

     Table_Index_Type     => Int,

     Table_Low_Bound      => 0,

     Table_Initial        => Alloc.Scope_Stack_Initial,

     Table_Increment      => Alloc.Scope_Stack_Increment,

     Table_Name           => "Sem.Scope_Stack");

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

   -- Subprograms --

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

   procedure Initialize;

   --  Initialize internal tables

   procedure Lock;

   --  Lock internal tables before calling back end

   procedure Semantics (Comp_Unit : Node_Id);

   --  This procedure is called to perform semantic analysis on the specified

   --  node which is the N_Compilation_Unit node for the unit.

   procedure Analyze (N : Node_Id);

   procedure Analyze (N : Node_Id; Suppress : Check_Id);

   --  This is the recursive procedure that is applied to individual nodes of

   --  the tree, starting at the top level node (compilation unit node) and

   --  then moving down the tree in a top down traversal. It calls individual

   --  routines with names Analyze_xxx to analyze node xxx. Each of these

   --  routines is responsible for calling Analyze on the components of the

   --  subtree.

   --

   --  Note: In the case of expression components (nodes whose Nkind is in

   --  N_Subexpr), the call to Analyze does not complete the semantic analysis

   --  of the node, since the type resolution cannot be completed until the

   --  complete context is analyzed. The completion of the type analysis occurs

   --  in the corresponding Resolve routine (see Sem_Res).

   --

   --  Note: for integer and real literals, the analyzer sets the flag to

   --  indicate that the result is a static expression. If the expander

   --  generates a literal that does NOT correspond to a static expression,

   --  e.g. by folding an expression whose value is known at compile-time,

   --  but is not technically static, then the caller should reset the

   --  Is_Static_Expression flag after analyzing but before resolving.

   --

   --  If the Suppress argument is present, then the analysis is done

   --  with the specified check suppressed (can be All_Checks to suppress

   --  all checks).

   procedure Analyze_List (L : List_Id);

   procedure Analyze_List (L : List_Id; Suppress : Check_Id);

   --  Analyzes each element of a list. If the Suppress argument is present,

   --  then the analysis is done with the specified check suppressed (can

   --  be All_Checks to suppress all checks).

   procedure Copy_Suppress_Status

     (C    : Check_Id;

      From : Entity_Id;

      To   : Entity_Id);

   --  If From is an entity for which check C is explicitly suppressed

   --  then also explicitly suppress the corresponding check in To.

   procedure Insert_List_After_And_Analyze

     (N : Node_Id; L : List_Id);

   procedure Insert_List_After_And_Analyze

     (N : Node_Id; L : List_Id; Suppress : Check_Id);

   --  Inserts list L after node N using Nlists.Insert_List_After, and then,

   --  after this insertion is complete, analyzes all the nodes in the list,

   --  including any additional nodes generated by this analysis. If the list

   --  is empty or No_List, the call has no effect. If the Suppress argument is

   --  present, then the analysis is done with the specified check suppressed

   --  (can be All_Checks to suppress all checks).

   procedure Insert_List_Before_And_Analyze

     (N : Node_Id; L : List_Id);

   procedure Insert_List_Before_And_Analyze

     (N : Node_Id; L : List_Id; Suppress : Check_Id);

   --  Inserts list L before node N using Nlists.Insert_List_Before, and then,

   --  after this insertion is complete, analyzes all the nodes in the list,

   --  including any additional nodes generated by this analysis. If the list

   --  is empty or No_List, the call has no effect. If the Suppress argument is

   --  present, then the analysis is done with the specified check suppressed

   --  (can be All_Checks to suppress all checks).

   procedure Insert_After_And_Analyze

     (N : Node_Id; M : Node_Id);

   procedure Insert_After_And_Analyze

     (N : Node_Id; M : Node_Id; Suppress : Check_Id);

   --  Inserts node M after node N and then after the insertion is complete,

   --  analyzes the inserted node and all nodes that are generated by

   --  this analysis. If the node is empty, the call has no effect. If the

   --  Suppress argument is present, then the analysis is done with the

   --  specified check suppressed (can be All_Checks to suppress all checks).

   procedure Insert_Before_And_Analyze

     (N : Node_Id; M : Node_Id);

   procedure Insert_Before_And_Analyze

     (N : Node_Id; M : Node_Id; Suppress : Check_Id);

   --  Inserts node M before node N and then after the insertion is complete,

   --  analyzes the inserted node and all nodes that could be generated by

   --  this analysis. If the node is empty, the call has no effect. If the

   --  Suppress argument is present, then the analysis is done with the

   --  specified check suppressed (can be All_Checks to suppress all checks).

   function External_Ref_In_Generic (E : Entity_Id) return Boolean;

   --  Return True if we are in the context of a generic and E is

   --  external (more global) to it.

   procedure Enter_Generic_Scope (S : Entity_Id);

   --  Shall be called each time a Generic subprogram or package scope is

   --  entered. S is the entity of the scope.

   --  ??? At the moment, only called for package specs because this mechanism

   --  is only used for avoiding freezing of external references in generics

   --  and this can only be an issue if the outer generic scope is a package

   --  spec (otherwise all external entities are already frozen)

   procedure Exit_Generic_Scope  (S : Entity_Id);

   --  Shall be called each time a Generic subprogram or package scope is

   --  exited. S is the entity of the scope.

   --  ??? At the moment, only called for package specs exit.

   function Explicit_Suppress (E : Entity_Id; C : Check_Id) return Boolean;

   --  This function returns True if an explicit pragma Suppress for check C

   --  is present in the package defining E.

   function Is_Check_Suppressed (E : Entity_Id; C : Check_Id) return Boolean;

   --  This function is called if Checks_May_Be_Suppressed (E) is True to

   --  determine whether check C is suppressed either on the entity E or

   --  as the result of a scope suppress pragma. If Checks_May_Be_Suppressed

   --  is False, then the status of the check can be determined simply by

   --  examining Scope_Checks (C), so this routine is not called in that case.

   generic

      with procedure Action (Item : Node_Id);

   procedure Walk_Library_Items;

   --  Primarily for use by SofCheck Inspector. Must be called after semantic

   --  analysis (and expansion) are complete. Walks each relevant library item,

   --  calling Action for each, in an order such that one will not run across

   --  forward references. Each Item passed to Action is the declaration or

   --  body of a library unit, including generics and renamings. The first item

   --  is the N_Package_Declaration node for package Standard. Bodies are not

   --  included, except for the main unit itself, which always comes last.

   --

   --  Item is never a subunit

   --

   --  Item is never an instantiation. Instead, the instance declaration is

   --  passed, and (if the instantiation is the main unit), the instance body.

end Sem;