151 lines
7.9 KiB
Ada
151 lines
7.9 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- S E M _ C A S E --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1996-2020, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING3. If not, go to --
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-- http://www.gnu.org/licenses for a complete copy of the license. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- Package containing the routines to process a list of discrete choices.
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-- Such lists can occur in two different constructs: case statements and
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-- record variants. We have factorized what used to be two very similar
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-- sets of routines in one place. These are not currently used for the
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-- aggregate case, since issues with nested aggregates make that case
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-- substantially different.
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-- The following processing is required for such cases:
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-- 1. Analysis of names of subtypes, constants, expressions appearing within
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-- the choices. This must be done when the construct is encountered to get
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-- proper visibility of names.
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-- 2. Checking for semantic correctness of the choices. A lot of this could
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-- be done at the time when the construct is encountered, but not all, since
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-- in the case of variants, statically predicated subtypes won't be frozen
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-- (and the choice sets known) till the enclosing record type is frozen. So
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-- at least the check for no overlaps and covering the range must be delayed
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-- till the freeze point in this case.
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-- 3. Set the Others_Discrete_Choices list for an others choice. This is
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-- used in various ways, e.g. to construct the disriminant checking function
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-- for the case of a variant with an others choice.
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-- 4. In the case of static predicates, we need to expand out choices that
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-- correspond to the predicate for the back end. This expansion destroys
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-- the list of choices, so it should be delayed to expansion time.
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-- Step 1 is performed by the generic procedure Analyze_Choices, which is
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-- called when the variant record or case statement/expression is first
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-- encountered.
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-- Step 2 is performed by the generic procedure Check_Choices. We decide to
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-- do all semantic checking in that step, since as noted above some of this
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-- has to be deferred to the freeze point in any case for variants. For case
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-- statements and expressions, this procedure can be called at the time the
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-- case construct is encountered (after calling Analyze_Choices).
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-- Step 3 is also performed by Check_Choices, since we need the static ranges
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-- for predicated subtypes to accurately construct this.
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-- Step 4 is performed by the procedure Expand_Static_Predicates_In_Choices.
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-- For case statements, this call only happens during expansion. The reason
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-- we do the expansion unconditionally for variants is that other processing,
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-- for example for aggregates, relies on having a complete list of choices.
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-- Historical note: We used to perform all four of these functions at once in
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-- a single procedure called Analyze_Choices. This routine was called at the
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-- time the construct was first encountered. That seemed to work OK up to Ada
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-- 2005, but the introduction of statically predicated subtypes with delayed
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-- evaluation of the static ranges made this completely wrong, both because
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-- the ASIS tree got destroyed by step 4, and steps 2 and 3 were too early
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-- in the variant record case.
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with Types; use Types;
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package Sem_Case is
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procedure No_OP (C : Node_Id);
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-- The no-operation routine. Does mostly nothing. Can be used
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-- in the following generics for the parameters Process_Empty_Choice,
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-- or Process_Associated_Node. In the case of an empty range choice,
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-- routine emits a warning when Warn_On_Redundant_Constructs is enabled.
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generic
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with procedure Process_Associated_Node (A : Node_Id);
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-- Associated with each case alternative or record variant A there is
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-- a node or list of nodes that need additional processing. This routine
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-- implements that processing.
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package Generic_Analyze_Choices is
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procedure Analyze_Choices
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(Alternatives : List_Id;
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Subtyp : Entity_Id);
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-- From a case expression, case statement, or record variant, this
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-- routine analyzes the corresponding list of discrete choices which
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-- appear in each element of the list Alternatives (for the variant
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-- part case, this is the variants, for a case expression or statement,
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-- this is the Alternatives).
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--
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-- Subtyp is the subtype of the discrete choices. The type against which
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-- the discrete choices must be resolved is its base type.
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end Generic_Analyze_Choices;
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generic
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with procedure Process_Empty_Choice (Choice : Node_Id);
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-- Processing to carry out for an empty Choice. Set to No_Op (declared
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-- above) if no such processing is required.
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with procedure Process_Non_Static_Choice (Choice : Node_Id);
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-- Processing to carry out for a non static Choice (gives an error msg)
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with procedure Process_Associated_Node (A : Node_Id);
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-- Associated with each case alternative or record variant A there is
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-- a node or list of nodes that need semantic processing. This routine
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-- implements that processing.
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package Generic_Check_Choices is
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procedure Check_Choices
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(N : Node_Id;
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Alternatives : List_Id;
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Subtyp : Entity_Id;
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Others_Present : out Boolean);
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-- From a case expression, case statement, or record variant N, this
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-- routine analyzes the corresponding list of discrete choices which
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-- appear in each element of the list Alternatives (for the variant
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-- part case, this is the variants, for a case expression or statement,
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-- this is the Alternatives).
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--
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-- Subtyp is the subtype of the discrete choices. The type against which
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-- the discrete choices must be resolved is its base type.
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--
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-- Others_Present is set to True if an Others choice is present in the
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-- list of choices, and in this case Others_Discrete_Choices is set in
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-- the N_Others_Choice node.
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--
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-- If a Discrete_Choice list contains at least one instance of a subtype
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-- with a static predicate, then the Has_SP_Choice flag is set true in
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-- the parent node (N_Variant, N_Case_Expression/Statement_Alternative).
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end Generic_Check_Choices;
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end Sem_Case;
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