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BuilderTransform.cpp
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//===--- BuilderTransform.cpp - Result-builder transformation -----------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file implements routines associated with the result-builder
// transformation.
//
//===----------------------------------------------------------------------===//
#include "MiscDiagnostics.h"
#include "TypeCheckAvailability.h"
#include "TypeChecker.h"
#include "swift/AST/ASTPrinter.h"
#include "swift/AST/ASTVisitor.h"
#include "swift/AST/ASTWalker.h"
#include "swift/AST/NameLookup.h"
#include "swift/AST/NameLookupRequests.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/TypeCheckRequests.h"
#include "swift/Basic/Assertions.h"
#include "swift/Sema/ConstraintSystem.h"
#include "swift/Sema/IDETypeChecking.h"
#include "swift/Sema/SolutionResult.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include <iterator>
#include <map>
#include <memory>
#include <tuple>
#include <utility>
using namespace swift;
using namespace constraints;
namespace {
/// Find the first #available condition within the statement condition,
/// or return NULL if there isn't one.
const StmtConditionElement *findAvailabilityCondition(StmtCondition stmtCond) {
for (const auto &cond : stmtCond) {
switch (cond.getKind()) {
case StmtConditionElement::CK_Boolean:
case StmtConditionElement::CK_PatternBinding:
case StmtConditionElement::CK_HasSymbol:
continue;
case StmtConditionElement::CK_Availability:
return &cond;
break;
}
}
return nullptr;
}
class ResultBuilderTransform
: private StmtVisitor<ResultBuilderTransform, NullablePtr<Stmt>,
NullablePtr<VarDecl>> {
friend StmtVisitor<ResultBuilderTransform, NullablePtr<Stmt>,
NullablePtr<VarDecl>>;
using UnsupportedElt = SkipUnhandledConstructInResultBuilder::UnhandledNode;
ASTContext &ctx;
DeclContext *dc;
ResultBuilder builder;
/// The source range of the body.
SourceRange bodyRange;
/// The result type of this result builder body.
Type ResultType;
/// The first recorded unsupported element discovered by the transformation.
UnsupportedElt FirstUnsupported;
public:
ResultBuilderTransform(ConstraintSystem &cs, DeclContext *dc,
SourceRange bodyRange, Type builderType, Type resultTy)
: ctx(cs.getASTContext()), dc(dc), builder(cs, dc, builderType),
bodyRange(bodyRange), ResultType(resultTy) {}
UnsupportedElt getUnsupportedElement() const { return FirstUnsupported; }
BraceStmt *apply(BraceStmt *braceStmt) {
auto newBody = visitBraceStmt(braceStmt, /*bodyVar=*/nullptr);
if (!newBody)
return nullptr;
return castToStmt<BraceStmt>(newBody.get());
}
VarDecl *getBuilderSelf() const { return builder.getBuilderSelf(); }
protected:
NullablePtr<Stmt> failTransform(UnsupportedElt unsupported) {
recordUnsupported(unsupported);
return nullptr;
}
VarDecl *recordVar(PatternBindingDecl *PB,
SmallVectorImpl<ASTNode> &container) {
container.push_back(PB);
container.push_back(PB->getSingleVar());
return PB->getSingleVar();
}
VarDecl *captureExpr(Expr *expr, SmallVectorImpl<ASTNode> &container) {
auto *var = builder.buildVar(expr->getStartLoc());
Pattern *pattern = NamedPattern::createImplicit(ctx, var);
auto *PB = PatternBindingDecl::createImplicit(
ctx, StaticSpellingKind::None, pattern, expr, dc, var->getStartLoc());
return recordVar(PB, container);
}
VarDecl *buildPlaceholderVar(SourceLoc loc,
SmallVectorImpl<ASTNode> &container,
Type type = Type(), Expr *initExpr = nullptr) {
auto *var = builder.buildVar(loc);
Pattern *placeholder = TypedPattern::createImplicit(
ctx, NamedPattern::createImplicit(ctx, var),
type ? type : PlaceholderType::get(ctx, var));
auto *PB = PatternBindingDecl::createImplicit(
ctx, StaticSpellingKind::None, placeholder, /*init=*/initExpr, dc,
var->getStartLoc());
return recordVar(PB, container);
}
AssignExpr *buildAssignment(VarDecl *dst, VarDecl *src) {
auto *dstRef = builder.buildVarRef(dst, /*Loc=*/SourceLoc());
auto *srcRef = builder.buildVarRef(src, /*Loc=*/SourceLoc());
return new (ctx) AssignExpr(dstRef, /*EqualLoc=*/SourceLoc(), srcRef,
/*Implicit=*/true);
}
AssignExpr *buildAssignment(VarDecl *dst, Expr *srcExpr) {
auto *dstRef = builder.buildVarRef(dst, /*Loc=*/SourceLoc());
return new (ctx) AssignExpr(dstRef, /*EqualLoc=*/SourceLoc(), srcExpr,
/*implicit=*/true);
}
void recordUnsupported(UnsupportedElt node) {
if (!FirstUnsupported)
FirstUnsupported = node;
}
#define UNSUPPORTED_STMT(StmtClass) \
NullablePtr<Stmt> visit##StmtClass##Stmt(StmtClass##Stmt *stmt, \
NullablePtr<VarDecl> var) { \
return failTransform(stmt); \
}
/// Visit the element of a brace statement, returning \c None if the element
/// was transformed successfully, or an unsupported element if the element
/// cannot be handled.
std::optional<UnsupportedElt>
transformBraceElement(ASTNode element, SmallVectorImpl<ASTNode> &newBody,
SmallVectorImpl<Expr *> &buildBlockArguments) {
if (auto *returnStmt = getAsStmt<ReturnStmt>(element)) {
assert(returnStmt->isImplicit());
element = returnStmt->getResult();
}
// Unwrap an implicit ThenStmt.
if (auto *thenStmt = getAsStmt<ThenStmt>(element)) {
if (thenStmt->isImplicit())
element = thenStmt->getResult();
}
if (auto *decl = element.dyn_cast<Decl *>()) {
switch (decl->getKind()) {
// Skip #warning/#error; we'll handle them when applying
// the builder.
case DeclKind::PoundDiagnostic:
case DeclKind::PatternBinding:
case DeclKind::Var:
case DeclKind::Param:
newBody.push_back(element);
return std::nullopt;
default:
return UnsupportedElt(decl);
}
llvm_unreachable("Unhandled case in switch!");
}
if (auto *stmt = element.dyn_cast<Stmt *>()) {
// Throw is allowed as is.
if (auto *throwStmt = dyn_cast<ThrowStmt>(stmt)) {
newBody.push_back(throwStmt);
return std::nullopt;
}
if (ctx.CompletionCallback && stmt->getSourceRange().isValid() &&
!containsIDEInspectionTarget(stmt->getSourceRange(), ctx.SourceMgr) &&
!isa<GuardStmt>(stmt)) {
// A statement that doesn't contain the code completion expression can't
// influence the type of the code completion expression, so we can skip
// it to improve performance.
return std::nullopt;
}
// Allocate variable with a placeholder type
auto *resultVar = buildPlaceholderVar(stmt->getStartLoc(), newBody);
auto result = visit(stmt, resultVar);
if (!result)
return UnsupportedElt(stmt);
newBody.push_back(result.get());
buildBlockArguments.push_back(
builder.buildVarRef(resultVar, stmt->getStartLoc()));
return std::nullopt;
}
auto *expr = element.get<Expr *>();
if (auto *SVE = dyn_cast<SingleValueStmtExpr>(expr)) {
// This should never be treated as an expression in a result builder, it
// should have statement semantics.
return transformBraceElement(SVE->getStmt(), newBody,
buildBlockArguments);
}
if (builder.supports(ctx.Id_buildExpression)) {
expr = builder.buildCall(expr->getStartLoc(), ctx.Id_buildExpression,
{expr}, {Identifier()});
}
if (isa<CodeCompletionExpr>(expr)) {
// Insert the CodeCompletionExpr directly into the buildBlock call. That
// way, we can extract the contextual type of the code completion token
// to rank code completion items that match the type expected by
// buildBlock higher.
buildBlockArguments.push_back(expr);
} else if (ctx.CompletionCallback && expr->getSourceRange().isValid() &&
containsIDEInspectionTarget(bodyRange, ctx.SourceMgr) &&
!containsIDEInspectionTarget(expr->getSourceRange(),
ctx.SourceMgr)) {
// A top-level expression that doesn't contain the code completion
// expression can't influence the type of the code completion expression
// if they're in the same result builder. Add a variable for it that we
// can put into the buildBlock call but don't add the expression itself
// into the transformed body to improve performance.
auto *resultVar = buildPlaceholderVar(expr->getStartLoc(), newBody);
buildBlockArguments.push_back(
builder.buildVarRef(resultVar, expr->getStartLoc()));
} else {
auto *capture = captureExpr(expr, newBody);
// A reference to the synthesized variable is passed as an argument
// to buildBlock.
buildBlockArguments.push_back(
builder.buildVarRef(capture, element.getStartLoc()));
}
return std::nullopt;
}
std::pair<NullablePtr<Expr>, std::optional<UnsupportedElt>>
transform(BraceStmt *braceStmt, SmallVectorImpl<ASTNode> &newBody) {
SmallVector<Expr *, 4> buildBlockArguments;
auto failTransform = [&](UnsupportedElt unsupported) {
return std::make_pair(nullptr, unsupported);
};
for (auto element : braceStmt->getElements()) {
if (auto unsupported =
transformBraceElement(element, newBody, buildBlockArguments)) {
// When in code completion mode, simply ignore unsported constructs to
// get results for anything that's unrelated to the unsupported
// constructs.
if (!ctx.CompletionCallback) {
return failTransform(*unsupported);
}
}
}
// Synthesize `buildBlock` or `buildPartial` based on captured arguments.
{
// If the builder supports `buildPartialBlock(first:)` and
// `buildPartialBlock(accumulated:next:)`, use this to combine
// sub-expressions pairwise.
if (!buildBlockArguments.empty() && builder.canUseBuildPartialBlock()) {
// let v0 = Builder.buildPartialBlock(first: arg_0)
// let v1 = Builder.buildPartialBlock(accumulated: v0, next: arg_1)
// ...
// let vN = Builder.buildPartialBlock(accumulated: vN-1, next: argN)
auto *buildPartialFirst = builder.buildCall(
braceStmt->getStartLoc(), ctx.Id_buildPartialBlock,
{buildBlockArguments.front()},
/*argLabels=*/{ctx.Id_first});
auto *buildBlockVar = captureExpr(buildPartialFirst, newBody);
for (auto *argExpr : llvm::drop_begin(buildBlockArguments)) {
auto *accumPartialBlock = builder.buildCall(
braceStmt->getStartLoc(), ctx.Id_buildPartialBlock,
{builder.buildVarRef(buildBlockVar, argExpr->getStartLoc()),
argExpr},
{ctx.Id_accumulated, ctx.Id_next});
buildBlockVar = captureExpr(accumPartialBlock, newBody);
}
return std::make_pair(
builder.buildVarRef(buildBlockVar, braceStmt->getStartLoc()),
std::nullopt);
}
// If `buildBlock` does not exist at this point, it could be the case that
// `buildPartialBlock` did not have the sufficient availability for this
// call site. Diagnose it.
else if (!builder.supports(ctx.Id_buildBlock)) {
ctx.Diags.diagnose(
braceStmt->getStartLoc(),
diag::result_builder_missing_available_buildpartialblock,
builder.getType());
return failTransform(braceStmt);
}
// Otherwise, call `buildBlock` on all subexpressions.
// Call Builder.buildBlock(... args ...)
auto *buildBlock = builder.buildCall(
braceStmt->getStartLoc(), ctx.Id_buildBlock, buildBlockArguments,
/*argLabels=*/{});
return std::make_pair(buildBlock, std::nullopt);
}
}
std::pair<bool, UnsupportedElt>
transform(BraceStmt *braceStmt, NullablePtr<VarDecl> bodyVar,
SmallVectorImpl<ASTNode> &elements) {
// Arguments passed to a synthesized `build{Partial}Block`.
SmallVector<Expr *, 4> buildBlockArguments;
auto failure = [&](UnsupportedElt element) {
return std::make_pair(true, element);
};
NullablePtr<Expr> buildBlockVarRef;
std::optional<UnsupportedElt> unsupported;
std::tie(buildBlockVarRef, unsupported) = transform(braceStmt, elements);
if (unsupported)
return failure(*unsupported);
// If this is not a top-level brace statement, we need to form an
// assignment from the `build{Partial}Block` call result variable
// to the provided one.
//
// Use start loc for the return statement so any contextual issues
// are attached to the beginning of the brace instead of its end.
auto resultLoc = braceStmt->getStartLoc();
if (bodyVar) {
elements.push_back(
new (ctx) AssignExpr(builder.buildVarRef(bodyVar.get(), resultLoc),
/*EqualLoc=*/SourceLoc(), buildBlockVarRef.get(),
/*Implicit=*/true));
} else {
Expr *buildBlockResult = buildBlockVarRef.get();
// Otherwise, it's a top-level brace and we need to synthesize
// a call to `buildFialBlock` if supported.
if (builder.supports(ctx.Id_buildFinalResult, {Identifier()})) {
buildBlockResult =
builder.buildCall(resultLoc, ctx.Id_buildFinalResult,
{buildBlockResult}, {Identifier()});
}
elements.push_back(
ReturnStmt::createImplicit(ctx, resultLoc, buildBlockResult));
}
return std::make_pair(false, UnsupportedElt());
}
BraceStmt *cloneBraceWith(BraceStmt *braceStmt,
SmallVectorImpl<ASTNode> &elements) {
auto lBrace = braceStmt ? braceStmt->getLBraceLoc() : SourceLoc();
auto rBrace = braceStmt ? braceStmt->getRBraceLoc() : SourceLoc();
bool implicit = braceStmt ? braceStmt->isImplicit() : true;
return BraceStmt::create(ctx, lBrace, elements, rBrace, implicit);
}
NullablePtr<Stmt> visitBraceStmt(BraceStmt *braceStmt,
NullablePtr<VarDecl> bodyVar) {
SmallVector<ASTNode, 4> elements;
bool failed;
UnsupportedElt unsupported;
std::tie(failed, unsupported) = transform(braceStmt, bodyVar, elements);
if (failed)
return failTransform(unsupported);
return cloneBraceWith(braceStmt, elements);
}
NullablePtr<Stmt> visitDoStmt(DoStmt *doStmt, NullablePtr<VarDecl> doVar) {
auto body = visitBraceStmt(doStmt->getBody(), doVar);
if (!body)
return nullptr;
return new (ctx) DoStmt(doStmt->getLabelInfo(), doStmt->getDoLoc(),
cast<BraceStmt>(body.get()), doStmt->isImplicit());
}
NullablePtr<Stmt> visitIfStmt(IfStmt *ifStmt, NullablePtr<VarDecl> ifVar) {
// Check whether the chain is buildable and whether it terminates
// without an `else`.
bool isOptional = false;
unsigned numPayloads = 0;
if (!isBuildableIfChain(ifStmt, numPayloads, isOptional))
return failTransform(ifStmt);
SmallVector<std::pair<Expr *, Stmt *>, 4> branchVarRefs;
auto transformed = transformIf(ifStmt, branchVarRefs);
if (!transformed)
return failTransform(ifStmt);
// Let's wrap `if` statement into a `do` and inject `type-join`
// operation with appropriate combination of `buildEither` that
// would get re-distributed after inference.
SmallVector<ASTNode, 4> doBody;
{
ifStmt = transformed.get();
// `if` goes first.
doBody.push_back(ifStmt);
assert(numPayloads == branchVarRefs.size());
SmallVector<Expr *, 4> buildEitherCalls;
for (unsigned i = 0; i != numPayloads; i++) {
Expr *branchVarRef;
Stmt *anchor;
std::tie(branchVarRef, anchor) = branchVarRefs[i];
auto *builderCall =
buildWrappedChainPayload(branchVarRef, i, numPayloads, isOptional);
// The operand should have optional type if we had optional results,
// so we just need to call `buildIf` now, since we're at the top level.
if (isOptional) {
builderCall = builder.buildCall(ifStmt->getThenStmt()->getStartLoc(),
builder.getBuildOptionalId(),
builderCall, /*argLabels=*/{});
}
buildEitherCalls.push_back(builderCall);
}
// If there is no `else` branch we need to build one.
// It consists a `buildOptional` call that uses `nil` as an argument.
//
// ```
// {
// $__builderResult = buildOptional(nil)
// }
// ```
//
// Type of `nil` is going to be inferred from `$__builderResult`.
if (!hasUnconditionalElse(ifStmt)) {
assert(isOptional);
auto *nil =
new (ctx) NilLiteralExpr(ifStmt->getEndLoc(), /*implicit=*/true);
buildEitherCalls.push_back(builder.buildCall(
/*loc=*/ifStmt->getEndLoc(), builder.getBuildOptionalId(), nil,
/*argLabels=*/{}));
}
auto *ifVarRef = builder.buildVarRef(ifVar.get(), ifStmt->getStartLoc());
doBody.push_back(TypeJoinExpr::create(ctx, ifVarRef, buildEitherCalls));
}
return DoStmt::createImplicit(ctx, LabeledStmtInfo(), doBody);
}
NullablePtr<IfStmt>
transformIf(IfStmt *ifStmt,
SmallVectorImpl<std::pair<Expr *, Stmt *>> &branchVarRefs) {
std::optional<UnsupportedElt> unsupported;
// If there is a #available in the condition, wrap the 'then' or 'else'
// in a call to buildLimitedAvailability(_:).
auto availabilityCond = findAvailabilityCondition(ifStmt->getCond());
bool supportsAvailability =
availabilityCond && builder.supports(ctx.Id_buildLimitedAvailability);
NullablePtr<Expr> thenVarRef;
NullablePtr<BraceStmt> thenBranch;
{
SmallVector<ASTNode, 4> thenBody;
auto *ifBraceStmt = cast<BraceStmt>(ifStmt->getThenStmt());
std::tie(thenVarRef, unsupported) = transform(ifBraceStmt, thenBody);
if (unsupported) {
recordUnsupported(*unsupported);
return nullptr;
}
if (supportsAvailability &&
!availabilityCond->getAvailability()->isUnavailability()) {
auto *builderCall = builder.buildCall(
ifBraceStmt->getStartLoc(), ctx.Id_buildLimitedAvailability,
{thenVarRef.get()}, {Identifier()});
thenVarRef = builder.buildVarRef(captureExpr(builderCall, thenBody),
ifBraceStmt->getStartLoc());
}
thenBranch = cloneBraceWith(ifBraceStmt, thenBody);
branchVarRefs.push_back({thenVarRef.get(), thenBranch.get()});
}
NullablePtr<Stmt> elseBranch;
if (auto *elseStmt = ifStmt->getElseStmt()) {
NullablePtr<Expr> elseVarRef;
if (auto *innerIfStmt = getAsStmt<IfStmt>(elseStmt)) {
elseBranch = transformIf(innerIfStmt, branchVarRefs);
if (!elseBranch) {
recordUnsupported(innerIfStmt);
return nullptr;
}
} else {
auto *elseBraceStmt = cast<BraceStmt>(elseStmt);
SmallVector<ASTNode> elseBody;
std::tie(elseVarRef, unsupported) = transform(elseBraceStmt, elseBody);
if (unsupported) {
recordUnsupported(*unsupported);
return nullptr;
}
// If there is a #unavailable in the condition, wrap the 'else' in a
// call to buildLimitedAvailability(_:).
if (supportsAvailability &&
availabilityCond->getAvailability()->isUnavailability()) {
auto *builderCall = builder.buildCall(
elseBraceStmt->getStartLoc(), ctx.Id_buildLimitedAvailability,
{elseVarRef.get()}, {Identifier()});
elseVarRef = builder.buildVarRef(captureExpr(builderCall, elseBody),
elseBraceStmt->getStartLoc());
}
elseBranch = cloneBraceWith(elseBraceStmt, elseBody);
branchVarRefs.push_back({elseVarRef.get(), elseBranch.get()});
}
}
return new (ctx)
IfStmt(ifStmt->getLabelInfo(), ifStmt->getIfLoc(), ifStmt->getCond(),
thenBranch.get(), ifStmt->getElseLoc(),
elseBranch.getPtrOrNull(), ifStmt->isImplicit());
}
NullablePtr<Stmt> visitSwitchStmt(SwitchStmt *switchStmt,
NullablePtr<VarDecl> switchVar) {
// For a do statement wrapping this switch that contains all of the
// `buildEither` calls that would get injected back into `case` bodies
// after solving is done.
//
// This is necessary because `buildEither requires type information from
// both sides to be available, so all case statements have to be
// type-checked first.
SmallVector<ASTNode, 4> doBody;
SmallVector<ASTNode, 4> cases;
SmallVector<Expr *, 4> caseVarRefs;
for (auto *caseStmt : switchStmt->getCases()) {
auto transformed = transformCase(caseStmt);
if (!transformed)
return failTransform(caseStmt);
cases.push_back(transformed->second);
caseVarRefs.push_back(transformed->first);
}
// If there are no 'case' statements in the body let's try
// to diagnose this situation via limited exhaustiveness check
// before failing a builder transform, otherwise type-checker
// might end up without any diagnostics which leads to crashes
// in SILGen.
if (caseVarRefs.empty()) {
TypeChecker::checkSwitchExhaustiveness(switchStmt, dc,
/*limitChecking=*/true);
return failTransform(switchStmt);
}
auto *transformedSwitch = SwitchStmt::create(
switchStmt->getLabelInfo(), switchStmt->getSwitchLoc(),
switchStmt->getSubjectExpr(), switchStmt->getLBraceLoc(), cases,
switchStmt->getRBraceLoc(), switchStmt->getEndLoc(), ctx);
doBody.push_back(transformedSwitch);
SmallVector<Expr *, 4> injectedExprs;
for (auto idx : indices(caseVarRefs)) {
auto *caseVarRef = caseVarRefs[idx];
// Build the expression that injects the case variable into appropriate
// buildEither(first:)/buildEither(second:) chain.
Expr *injectedCaseExpr = buildWrappedChainPayload(
caseVarRef, idx, caseVarRefs.size(), /*isOptional=*/false);
injectedExprs.push_back(injectedCaseExpr);
}
auto *switchVarRef =
builder.buildVarRef(switchVar.get(), switchStmt->getEndLoc());
doBody.push_back(TypeJoinExpr::create(ctx, switchVarRef, injectedExprs));
return DoStmt::createImplicit(ctx, LabeledStmtInfo(), doBody);
}
std::optional<std::pair<Expr *, CaseStmt *>>
transformCase(CaseStmt *caseStmt) {
auto *body = caseStmt->getBody();
// Explicitly disallow `case` statements with empty bodies
// since that helps to diagnose other issues with switch
// statements by excluding invalid cases.
if (auto *BS = dyn_cast<BraceStmt>(body)) {
if (BS->getNumElements() == 0) {
// HACK: still allow empty bodies if typechecking for code
// completion. Code completion ignores diagnostics
// and won't get any types if we fail.
if (!ctx.SourceMgr.hasIDEInspectionTargetBuffer())
return std::nullopt;
}
}
NullablePtr<Expr> caseVarRef;
std::optional<UnsupportedElt> unsupported;
SmallVector<ASTNode, 4> newBody;
std::tie(caseVarRef, unsupported) = transform(body, newBody);
if (unsupported) {
recordUnsupported(*unsupported);
return std::nullopt;
}
auto *newCase = CaseStmt::create(
ctx, caseStmt->getParentKind(), caseStmt->getLoc(),
caseStmt->getCaseLabelItems(),
caseStmt->hasUnknownAttr() ? caseStmt->getStartLoc() : SourceLoc(),
caseStmt->getItemTerminatorLoc(), cloneBraceWith(body, newBody),
caseStmt->getCaseBodyVariablesOrEmptyArray(), caseStmt->isImplicit(),
caseStmt->getFallthroughStmt());
return std::make_pair(caseVarRef.get(), newCase);
}
/// do {
/// var $__forEach = []
/// for ... in ... {
/// ...
/// $__builderVar = buildBlock(...)
/// $__forEach.append($__builderVar)
/// }
/// buildArray($__forEach)
/// }
NullablePtr<Stmt> visitForEachStmt(ForEachStmt *forEachStmt,
NullablePtr<VarDecl> forEachVar) {
// for...in statements are handled via buildArray(_:); bail out if the
// builder does not support it.
if (!builder.supports(ctx.Id_buildArray))
return failTransform(forEachStmt);
// For-each statements require the Sequence protocol. If we don't have
// it (which generally means the standard library isn't loaded), fall
// out of the result-builder path entirely to let normal type checking
// take care of this.
auto sequenceProto = TypeChecker::getProtocol(
dc->getASTContext(), forEachStmt->getForLoc(),
forEachStmt->getAwaitLoc().isValid() ? KnownProtocolKind::AsyncSequence
: KnownProtocolKind::Sequence);
if (!sequenceProto)
return failTransform(forEachStmt);
SmallVector<ASTNode, 4> doBody;
SourceLoc endLoc = forEachStmt->getEndLoc();
// Build a variable that is going to hold array of results produced
// by each iteration of the loop.
//
// Not that it's not going to be initialized here, that would happen
// only when a solution is found.
VarDecl *arrayVar = buildPlaceholderVar(
forEachStmt->getEndLoc(), doBody,
ArraySliceType::get(PlaceholderType::get(ctx, forEachVar.get())),
ArrayExpr::create(ctx, /*LBrace=*/endLoc, /*Elements=*/{},
/*Commas=*/{}, /*RBrace=*/endLoc));
NullablePtr<Expr> bodyVarRef;
std::optional<UnsupportedElt> unsupported;
SmallVector<ASTNode, 4> newBody;
{
std::tie(bodyVarRef, unsupported) =
transform(forEachStmt->getBody(), newBody);
if (unsupported)
return failTransform(*unsupported);
// Form a call to Array.append(_:) to add the result of executing each
// iteration of the loop body to the array formed above.
{
auto arrayVarRef = builder.buildVarRef(arrayVar, endLoc);
auto arrayAppendRef = new (ctx) UnresolvedDotExpr(
arrayVarRef, endLoc, DeclNameRef(ctx.getIdentifier("append")),
DeclNameLoc(endLoc), /*implicit=*/true);
arrayAppendRef->setFunctionRefKind(FunctionRefKind::SingleApply);
auto *argList = ArgumentList::createImplicit(
ctx, endLoc, {Argument::unlabeled(bodyVarRef.get())}, endLoc);
newBody.push_back(
CallExpr::createImplicit(ctx, arrayAppendRef, argList));
}
}
auto *newForEach = new (ctx)
ForEachStmt(forEachStmt->getLabelInfo(), forEachStmt->getForLoc(),
forEachStmt->getTryLoc(), forEachStmt->getAwaitLoc(),
forEachStmt->getPattern(), forEachStmt->getInLoc(),
forEachStmt->getParsedSequence(),
forEachStmt->getWhereLoc(), forEachStmt->getWhere(),
cloneBraceWith(forEachStmt->getBody(), newBody),
forEachStmt->isImplicit());
// For a body of new `do` statement that holds updated `for-in` loop
// and epilog that consists of a call to `buildArray` that forms the
// final result.
{
// Modified `for { ... }`
doBody.push_back(newForEach);
// $__forEach = buildArray($__arrayVar)
doBody.push_back(buildAssignment(
forEachVar.get(),
builder.buildCall(forEachStmt->getEndLoc(), ctx.Id_buildArray,
{builder.buildVarRef(arrayVar, endLoc)},
{Identifier()})));
}
return DoStmt::createImplicit(ctx, LabeledStmtInfo(), doBody);
}
UNSUPPORTED_STMT(Throw)
UNSUPPORTED_STMT(Return)
UNSUPPORTED_STMT(Yield)
UNSUPPORTED_STMT(Then)
UNSUPPORTED_STMT(Discard)
UNSUPPORTED_STMT(Defer)
UNSUPPORTED_STMT(Guard)
UNSUPPORTED_STMT(While)
UNSUPPORTED_STMT(DoCatch)
UNSUPPORTED_STMT(RepeatWhile)
UNSUPPORTED_STMT(Break)
UNSUPPORTED_STMT(Continue)
UNSUPPORTED_STMT(Fallthrough)
UNSUPPORTED_STMT(Fail)
UNSUPPORTED_STMT(PoundAssert)
UNSUPPORTED_STMT(Case)
#undef UNSUPPORTED_STMT
private:
static bool isBuildableIfChainRecursive(IfStmt *ifStmt, unsigned &numPayloads,
bool &isOptional) {
// The 'then' clause contributes a payload.
++numPayloads;
// If there's an 'else' clause, it contributes payloads:
if (auto elseStmt = ifStmt->getElseStmt()) {
// If it's 'else if', it contributes payloads recursively.
if (auto elseIfStmt = dyn_cast<IfStmt>(elseStmt)) {
return isBuildableIfChainRecursive(elseIfStmt, numPayloads, isOptional);
// Otherwise it's just the one.
} else {
++numPayloads;
}
// If not, the chain result is at least optional.
} else {
isOptional = true;
}
return true;
}
static bool hasUnconditionalElse(IfStmt *ifStmt) {
if (auto *elseStmt = ifStmt->getElseStmt()) {
if (auto *ifStmt = dyn_cast<IfStmt>(elseStmt))
return hasUnconditionalElse(ifStmt);
return true;
}
return false;
}
bool isBuildableIfChain(IfStmt *ifStmt, unsigned &numPayloads,
bool &isOptional) {
if (!isBuildableIfChainRecursive(ifStmt, numPayloads, isOptional))
return false;
// If there's a missing 'else', we need 'buildOptional' to exist.
if (isOptional && !builder.supportsOptional())
return false;
// If there are multiple clauses, we need 'buildEither(first:)' and
// 'buildEither(second:)' to both exist.
if (numPayloads > 1) {
if (!builder.supports(ctx.Id_buildEither, {ctx.Id_first}) ||
!builder.supports(ctx.Id_buildEither, {ctx.Id_second}))
return false;
}
return true;
}
/// Wrap a payload value in an expression which will produce a chain
/// result (without `buildIf`).
Expr *buildWrappedChainPayload(Expr *operand, unsigned payloadIndex,
unsigned numPayloads, bool isOptional) {
assert(payloadIndex < numPayloads);
// Inject into the appropriate chain position.
//
// We produce a (left-biased) balanced binary tree of Eithers in order
// to prevent requiring a linear number of injections in the worst case.
// That is, if we have 13 clauses, we want to produce:
//
// /------------------Either------------\
// /-------Either-------\ /--Either--\
// /--Either--\ /--Either--\ /--Either--\ \
// /-E-\ /-E-\ /-E-\ /-E-\ /-E-\ /-E-\ \
// 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100
//
// Note that a prefix of length D of the payload index acts as a path
// through the tree to the node at depth D. On the rightmost path
// through the tree (when this prefix is equal to the corresponding
// prefix of the maximum payload index), the bits of the index mark
// where Eithers are required.
//
// Since we naturally want to build from the innermost Either out, and
// therefore work with progressively shorter prefixes, we can do it all
// with right-shifts.
for (auto path = payloadIndex, maxPath = numPayloads - 1; maxPath != 0;
path >>= 1, maxPath >>= 1) {
// Skip making Eithers on the rightmost path where they aren't required.
// This isn't just an optimization: adding spurious Eithers could
// leave us with unresolvable type variables if `buildEither` has
// a signature like:
// static func buildEither<T,U>(first value: T) -> Either<T,U>
// which relies on unification to work.
if (path == maxPath && !(maxPath & 1))
continue;
bool isSecond = (path & 1);
operand =
builder.buildCall(operand->getStartLoc(), ctx.Id_buildEither, operand,
{isSecond ? ctx.Id_second : ctx.Id_first});
}
// Inject into Optional if required. We'll be adding the call to
// `buildIf` after all the recursive calls are complete.
if (isOptional) {
operand = buildSomeExpr(operand);
}
return operand;
}
Expr *buildSomeExpr(Expr *arg) {
auto optionalDecl = ctx.getOptionalDecl();
auto optionalType = optionalDecl->getDeclaredType();
auto loc = arg->getStartLoc();
auto optionalTypeExpr =
TypeExpr::createImplicitHack(loc, optionalType, ctx);
auto someRef = new (ctx) UnresolvedDotExpr(
optionalTypeExpr, loc, DeclNameRef(ctx.getIdentifier("some")),
DeclNameLoc(loc), /*implicit=*/true);
auto *argList = ArgumentList::forImplicitUnlabeled(ctx, {arg});
return CallExpr::createImplicit(ctx, someRef, argList);
}
Expr *buildNoneExpr(SourceLoc endLoc) {
auto optionalDecl = ctx.getOptionalDecl();
auto optionalType = optionalDecl->getDeclaredType();
auto optionalTypeExpr =
TypeExpr::createImplicitHack(endLoc, optionalType, ctx);
return new (ctx) UnresolvedDotExpr(optionalTypeExpr, endLoc,
DeclNameRef(ctx.getIdentifier("none")),
DeclNameLoc(endLoc), /*implicit=*/true);
}
};
} // end anonymous namespace
std::optional<BraceStmt *>
TypeChecker::applyResultBuilderBodyTransform(FuncDecl *func, Type builderType) {
// First look for any return statements, and bail if we have any.
auto &ctx = func->getASTContext();
if (evaluateOrDefault(ctx.evaluator, BraceHasReturnRequest{func->getBody()},
false)) {
// One or more explicit 'return' statements were encountered, which
// disables the result builder transform. Warn when we do this.
auto returnStmts = findReturnStatements(func);
assert(!returnStmts.empty());
ctx.Diags.diagnose(
returnStmts.front()->getReturnLoc(),
diag::result_builder_disabled_by_return_warn, builderType);
// Note that one can remove the result builder attribute.
auto attr = func->getAttachedResultBuilder();
if (!attr) {
if (auto accessor = dyn_cast<AccessorDecl>(func)) {
attr = accessor->getStorage()->getAttachedResultBuilder();
}
}
if (attr) {
diagnoseAndRemoveAttr(func, attr, diag::result_builder_remove_attr);
}
// Note that one can remove all of the return statements.
{
auto diag = ctx.Diags.diagnose(
returnStmts.front()->getReturnLoc(),
diag::result_builder_remove_returns);
for (auto returnStmt : returnStmts) {
diag.fixItRemove(returnStmt->getReturnLoc());
}
}
return std::nullopt;
}
auto target = SyntacticElementTarget(func);
if (ConstraintSystem::preCheckTarget(target))
return nullptr;
ConstraintSystemOptions options = ConstraintSystemFlags::AllowFixes;
auto resultInterfaceTy = func->getResultInterfaceType();
auto resultContextType = func->mapTypeIntoContext(resultInterfaceTy);
// Determine whether we're inferring the underlying type for the opaque
// result type of this function.
ConstraintKind resultConstraintKind = ConstraintKind::Conversion;
if (auto opaque = resultContextType->getAs<OpaqueTypeArchetypeType>()) {
if (opaque->getDecl()->isOpaqueReturnTypeOfFunction(func)) {
resultConstraintKind = ConstraintKind::Equal;
}
}
// Build a constraint system in which we can check the body of the function.
ConstraintSystem cs(func, options);
if (cs.isDebugMode()) {
auto &log = llvm::errs();
log << "--- Applying result builder to function ---\n";
func->dump(log);
log << '\n';
}
// Map type parameters into context. We don't want type
// parameters to appear in the result builder type, because
// the result builder type will only be used inside the body
// of this decl; it's not part of the interface type.
builderType = func->mapTypeIntoContext(builderType);
if (auto result = cs.matchResultBuilder(
func, builderType, resultContextType, resultConstraintKind,
/*contextualType=*/Type(),
cs.getConstraintLocator(func->getBody()))) {
if (result->isFailure())
return nullptr;
}
// Solve the constraint system.
if (cs.getASTContext().CompletionCallback) {