Enforce case label uniqueness and constness

1 files changed, 155 insertions, 0 deletions

diff --git a/boot/validation.cc b/boot/validation.cc
new file mode 100644
index 0000000..ccc8865
--- /dev/null
+++ b/boot/validation.cc
@@ -0,0 +1,155 @@
+/* Final validation after constant folding.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT 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
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "elna/boot/validation.h"
+
+#include <algorithm>
+#include <numeric>
+#include <unordered_map>
+
+namespace elna::boot
+{
+    validation_error::validation_error(const source_position position, payload_type payload)
+        : error(position), payload(std::move(payload))
+    {
+    }
+
+    std::string validation_error::what() const
+    {
+        return std::visit([](const auto& payload) -> std::string {
+            using T = std::decay_t<decltype(payload)>;
+
+            if constexpr (std::is_same_v<T, non_constant_initializer>)
+            {
+                return "Variable initializers must be constant expressions";
+            }
+            else if constexpr (std::is_same_v<T, duplicate_case>)
+            {
+                return "Duplicate case label";
+            }
+            else if constexpr (std::is_same_v<T, non_constant_case_label>)
+            {
+                return "Case label must be a constant expression";
+            }
+        }, this->payload);
+    }
+
+    std::optional<std::pair<std::string, source_position>> validation_error::note() const
+    {
+        return std::visit([](const auto& payload) -> std::optional<std::pair<std::string, source_position>> {
+            using T = std::decay_t<decltype(payload)>;
+
+            if constexpr (std::is_same_v<T, non_constant_initializer>)
+            {
+                std::string identifier_list = std::accumulate(
+                        std::next(payload.identifiers.begin()), payload.identifiers.end(),
+                        payload.identifiers.front().name(),
+                        [](const std::string& accumulator, const identifier& next) -> std::string {
+                            return accumulator + ", " + next.name();
+                        });
+                auto position_span = source_position(payload.identifiers.front().position().start(),
+                        payload.identifiers.back().position().end());
+                return std::make_pair(std::move(identifier_list), position_span);
+            }
+            else if constexpr (std::is_same_v<T, duplicate_case>)
+            {
+                return std::make_pair("Previous label here", payload.first);
+            }
+            else if constexpr (std::is_same_v<T, non_constant_case_label>)
+            {
+                return std::nullopt;
+            }
+        }, this->payload);
+    }
+
+    validation_error validation_error::non_constant_initializer_error(const source_position position,
+            const std::vector<identifier_definition>& identifiers)
+    {
+        non_constant_initializer payload;
+        payload.identifiers.reserve(identifiers.size());
+
+        std::ranges::transform(identifiers, std::back_inserter(payload.identifiers),
+                [](const auto& identifier) { return identifier.id(); });
+
+        return validation_error(position, std::move(payload));
+    }
+
+    validation_visitor::validation_visitor(symbol_bag& bag, const target_info& target)
+        : bag(bag), target(target), constant_evaluator(this->bag, this->target)
+    {
+    }
+
+    void validation_visitor::visit(variable_declaration* declaration)
+    {
+        if (declaration->initializer == nullptr || has_errors())
+        {
+            return;
+        }
+        auto computed = this->constant_evaluator.evaluate(*declaration->initializer);
+        if (!computed)
+        {
+            auto non_constant_initializer_error = validation_error::non_constant_initializer_error(
+                    declaration->initializer->position(), declaration->identifiers);
+            add_error<validation_error>(non_constant_initializer_error);
+            return;
+        }
+        for (const auto& identifier : declaration->identifiers)
+        {
+            auto variable_symbol = this->bag.lookup(identifier.name())->is_variable();
+            variable_symbol->value = computed;
+        }
+    }
+
+    void validation_visitor::visit(procedure_declaration *declaration)
+    {
+        if (declaration->body.has_value())
+        {
+            auto procedure = this->bag.lookup(declaration->identifier.name())->is_procedure();
+            this->bag.enter(procedure->scope);
+        }
+        walking_visitor::visit(declaration);
+        if (declaration->body.has_value())
+        {
+            this->bag.leave();
+        }
+    }
+
+    void validation_visitor::visit(case_statement *statement)
+    {
+        walking_visitor::visit(statement);
+        std::unordered_map<constant_value, source_position, constant_value_hash, constant_value_hash> seen;
+        for (const auto& case_block : statement->cases)
+        {
+            for (auto *label : case_block.labels)
+            {
+                auto value = this->constant_evaluator.evaluate(*label);
+                if (!value.has_value())
+                {
+                    add_error<validation_error>(label->position(),
+                            validation_error::non_constant_case_label{});
+                    continue;
+                }
+                auto [case_position, inserted] = seen.try_emplace(value.value(), label->position());
+                if (!inserted)
+                {
+                    add_error<validation_error>(label->position(),
+                            validation_error::duplicate_case{ case_position->second });
+                }
+            }
+        }
+    }
+}