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Implement unused pattern bindings, continued (#6518)

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Implementation of unused pattern bindings #2022, continued.

Whereas previous PR #6460 took care of parsing, and PR #6479 prepared
the stage by using _ in some test cases, this PR has the the actual
implementation, using a simple dataflow analysis.

---------

Co-authored-by: Burak Emir <bqe@google.com>
Co-authored-by: jonmeow <jperkins@google.com>
This commit is contained in:
Burak Emir
2026-02-19 23:33:36 +00:00
committed by GitHub
co-authored by Burak Emir jonmeow
parent bea24a8bee
commit fdb188ccfd
366 changed files with 8453 additions and 7996 deletions
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toolchain/check/handle_function.cpp
+69 -7
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@@ -10,22 +10,19 @@
#include "toolchain/check/control_flow.h"
#include "toolchain/check/convert.h"
#include "toolchain/check/decl_introducer_state.h"
#include "toolchain/check/decl_name_stack.h"
#include "toolchain/check/function.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/handle.h"
#include "toolchain/check/import.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/interface.h"
#include "toolchain/check/keyword_modifier_set.h"
#include "toolchain/check/literal.h"
#include "toolchain/check/merge.h"
#include "toolchain/check/modifiers.h"
#include "toolchain/check/name_component.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/return.h"
#include "toolchain/check/type.h"
#include "toolchain/check/type_completion.h"
#include "toolchain/check/unused.h"
#include "toolchain/lex/token_kind.h"
#include "toolchain/parse/node_ids.h"
#include "toolchain/sem_ir/builtin_function_kind.h"
@@ -607,8 +604,73 @@ static auto BuildFunctionDecl(Context& context,
return {function_decl.function_id, decl_id};
}
// Checks that "unused" marker is only used in definitions, and emits a
// diagnostic for every binding that is marked unused.
static auto CheckUnusedBindingsInPattern(Context& context,
SemIR::InstId pattern_id) -> void {
llvm::SmallVector<SemIR::InstId> work_list;
work_list.push_back(pattern_id);
while (!work_list.empty()) {
auto current_id = work_list.pop_back_val();
auto inst = context.insts().Get(current_id);
CARBON_KIND_SWITCH(inst) {
case SemIR::OutParamPattern::Kind:
case SemIR::RefParamPattern::Kind:
case SemIR::ValueParamPattern::Kind:
case SemIR::VarParamPattern::Kind: {
auto param = inst.As<SemIR::AnyParamPattern>();
work_list.push_back(param.subpattern_id);
break;
}
case SemIR::RefBindingPattern::Kind:
case SemIR::SymbolicBindingPattern::Kind:
case SemIR::ValueBindingPattern::Kind: {
auto bind = inst.As<SemIR::AnyBindingPattern>();
auto& entity_name = context.entity_names().Get(bind.entity_name_id);
// We need special treatment for the name "_" which is implicitly
// unused but actually permitted in declarations.
if (entity_name.is_unused &&
entity_name.name_id != SemIR::NameId::Underscore) {
CARBON_DIAGNOSTIC(UnusedModifierOnDeclaration, Error,
"`unused` modifier on declaration");
context.emitter().Emit(current_id, UnusedModifierOnDeclaration);
}
break;
}
case CARBON_KIND(SemIR::VarPattern var_pattern): {
work_list.push_back(var_pattern.subpattern_id);
break;
}
case CARBON_KIND(SemIR::TuplePattern tuple_pattern): {
auto elements = context.inst_blocks().Get(tuple_pattern.elements_id);
for (auto element_id : llvm::reverse(elements)) {
work_list.push_back(element_id);
}
break;
}
default:
break;
}
}
}
static auto DiagnoseUnusedMarkersInDeclaration(Context& context,
SemIR::FunctionId function_id)
-> void {
const auto& function = context.functions().Get(function_id);
if (function.param_patterns_id.has_value()) {
for (auto pattern_id :
context.inst_blocks().Get(function.param_patterns_id)) {
CheckUnusedBindingsInPattern(context, pattern_id);
}
}
}
auto HandleParseNode(Context& context, Parse::FunctionDeclId node_id) -> bool {
BuildFunctionDecl(context, node_id, /*is_definition=*/false);
auto [function_id, decl_id] =
BuildFunctionDecl(context, node_id, /*is_definition=*/false);
DiagnoseUnusedMarkersInDeclaration(context, function_id);
context.decl_name_stack().PopScope();
return true;
}
@@ -672,7 +734,7 @@ auto HandleParseNode(Context& context, Parse::FunctionDefinitionId node_id)
}
FinishFunctionDefinition(context, function_id);
context.decl_name_stack().PopScope();
context.decl_name_stack().PopScope(/*check_unused=*/true);
return true;
}