lib/Parse/ParseGeneric.cpp - third_party/swift - Git at Google

 //===--- ParseGeneric.cpp - Swift Language Parser for Generics ------------===//
 //
 // This source file is part of the Swift.org open source project
 //
 // Copyright (c) 2014 - 2017 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
 //
 //===----------------------------------------------------------------------===//
 //
 // Generic Parsing and AST Building
 //
 //===----------------------------------------------------------------------===//

 #include "swift/Parse/Parser.h"
 #include "swift/AST/DiagnosticsParse.h"
 #include "swift/Parse/CodeCompletionCallbacks.h"
 #include "swift/Parse/Lexer.h"
 #include "swift/Syntax/SyntaxBuilders.h"
 #include "swift/Syntax/SyntaxNodes.h"
 #include "swift/Syntax/SyntaxParsingContext.h"
 using namespace swift;
 using namespace swift::syntax;

 /// parseGenericParameters - Parse a sequence of generic parameters, e.g.,
 /// < T : Comparable, U : Container> along with an optional requires clause.
 ///
 ///   generic-params:
 ///     '<' generic-param (',' generic-param)* where-clause? '>'
 ///
 ///   generic-param:
 ///     identifier
 ///     identifier ':' type-identifier
 ///     identifier ':' type-composition
 ///
 /// When parsing the generic parameters, this routine establishes a new scope
 /// and adds those parameters to the scope.
 ParserResult<GenericParamList> Parser::parseGenericParameters() {
   SyntaxParsingContext GPSContext(SyntaxContext, SyntaxKind::GenericParameterClause);
   // Parse the opening '<'.
   assert(startsWithLess(Tok) && "Generic parameter list must start with '<'");
   return parseGenericParameters(consumeStartingLess());
 }

 ParserStatus
 Parser::parseGenericParametersBeforeWhere(SourceLoc LAngleLoc,
                         SmallVectorImpl<GenericTypeParamDecl *> &GenericParams) {
   ParserStatus Result;
   SyntaxParsingContext GPSContext(SyntaxContext, SyntaxKind::GenericParameterList);
   bool HasNextParam;
   do {
     SyntaxParsingContext GParamContext(SyntaxContext, SyntaxKind::GenericParameter);
     // Note that we're parsing a declaration.
     StructureMarkerRAII ParsingDecl(*this, Tok.getLoc(),
                                     StructureMarkerKind::Declaration);

     // Parse attributes.
     DeclAttributes attributes;
     if (Tok.hasComment())
       attributes.add(new (Context) RawDocCommentAttr(Tok.getCommentRange()));
     bool foundCCTokenInAttr;
     parseDeclAttributeList(attributes, foundCCTokenInAttr);

     // Parse the name of the parameter.
     Identifier Name;
     SourceLoc NameLoc;
     if (parseIdentifier(Name, NameLoc,
                         diag::expected_generics_parameter_name)) {
       Result.setIsParseError();
       break;
     }

     // Parse the ':' followed by a type.
     SmallVector<TypeLoc, 1> Inherited;
     if (Tok.is(tok::colon)) {
       (void)consumeToken();
       ParserResult<TypeRepr> Ty;

       if (Tok.isAny(tok::identifier, tok::code_complete, tok::kw_protocol,
                     tok::kw_Any)) {
         Ty = parseType();
       } else if (Tok.is(tok::kw_class)) {
         diagnose(Tok, diag::unexpected_class_constraint);
         diagnose(Tok, diag::suggest_anyobject)
         .fixItReplace(Tok.getLoc(), "AnyObject");
         consumeToken();
         Result.setIsParseError();
       } else {
         diagnose(Tok, diag::expected_generics_type_restriction, Name);
         Result.setIsParseError();
       }

       if (Ty.hasCodeCompletion())
         return makeParserCodeCompletionStatus();

       if (Ty.isNonNull())
         Inherited.push_back(Ty.get());
     }

     // We always create generic type parameters with an invalid depth.
     // Semantic analysis fills in the depth when it processes the generic
     // parameter list.
     auto Param = new (Context) GenericTypeParamDecl(CurDeclContext, Name, NameLoc,
                                             GenericTypeParamDecl::InvalidDepth,
                                                     GenericParams.size());
     if (!Inherited.empty())
       Param->setInherited(Context.AllocateCopy(Inherited));
     GenericParams.push_back(Param);

     // Attach attributes.
     Param->getAttrs() = attributes;

     // Add this parameter to the scope.
     addToScope(Param);

     // Parse the comma, if the list continues.
     HasNextParam = consumeIf(tok::comma);
   } while (HasNextParam);

   return Result;
 }

 ParserResult<GenericParamList>
 Parser::parseGenericParameters(SourceLoc LAngleLoc) {
   // Parse the generic parameter list.
   SmallVector<GenericTypeParamDecl *, 4> GenericParams;
   auto Result = parseGenericParametersBeforeWhere(LAngleLoc, GenericParams);

   // Return early if there was code completion token.
   if (Result.hasCodeCompletion())
     return Result;
   auto Invalid = Result.isError();

   // Parse the optional where-clause.
   SourceLoc WhereLoc;
   SmallVector<RequirementRepr, 4> Requirements;
   bool FirstTypeInComplete;
   if (Tok.is(tok::kw_where) &&
       parseGenericWhereClause(WhereLoc, Requirements,
                               FirstTypeInComplete).isError()) {
     Invalid = true;
   }

   // Parse the closing '>'.
   SourceLoc RAngleLoc;
   if (startsWithGreater(Tok)) {
     RAngleLoc = consumeStartingGreater();
   } else {
     if (!Invalid) {
       diagnose(Tok, diag::expected_rangle_generics_param);
       diagnose(LAngleLoc, diag::opening_angle);
       Invalid = true;
     }

     // Skip until we hit the '>'.
     RAngleLoc = skipUntilGreaterInTypeList();
   }

   if (GenericParams.empty())
     return nullptr;

   return makeParserResult(GenericParamList::create(Context, LAngleLoc,
                                                    GenericParams, WhereLoc,
                                                    Requirements, RAngleLoc));
 }

 ParserResult<GenericParamList> Parser::maybeParseGenericParams() {
   if (!startsWithLess(Tok))
     return nullptr;

   if (!isInSILMode())
     return parseGenericParameters();

   // In SIL mode, we can have multiple generic parameter lists, with the
   // first one being the outmost generic parameter list.
   GenericParamList *gpl = nullptr, *outer_gpl = nullptr;
   do {
     gpl = parseGenericParameters().getPtrOrNull();
     if (!gpl)
       return nullptr;

     if (outer_gpl)
       gpl->setOuterParameters(outer_gpl);
     outer_gpl = gpl;
   } while (startsWithLess(Tok));
   return makeParserResult(gpl);
 }

 void
 Parser::diagnoseWhereClauseInGenericParamList(const GenericParamList *
                                               GenericParams) {
   if (GenericParams == nullptr || GenericParams->getWhereLoc().isInvalid())
     return;


   auto WhereRangeInsideBrackets = GenericParams->getWhereClauseSourceRange();

   // Move everything immediately following the last generic parameter
   // as written all the way to the right angle bracket (">")
   auto LastGenericParam = GenericParams->getParams().back();
   auto EndOfLastGenericParam =
       Lexer::getLocForEndOfToken(SourceMgr, LastGenericParam->getEndLoc());

   CharSourceRange RemoveWhereRange { SourceMgr,
     EndOfLastGenericParam,
     GenericParams->getRAngleLoc()
   };

   auto WhereCharRange =
     Lexer::getCharSourceRangeFromSourceRange(SourceMgr,
                                   GenericParams->getWhereClauseSourceRange());

   SmallString<64> Buffer;
   llvm::raw_svector_ostream WhereClauseText(Buffer);
   WhereClauseText << SourceMgr.extractText(Tok.is(tok::kw_where)
                                            ? WhereCharRange
                                            : RemoveWhereRange);

   // If, for some reason, there was a where clause in both locations, we're
   // adding to the list of requirements, so tack on a comma here before
   // inserting it at the head of the later where clause.
   if (Tok.is(tok::kw_where))
     WhereClauseText << ',';

   // For Swift 3, keep this warning.
   const auto Message = Context.isSwiftVersion3()
                              ? diag::swift3_where_inside_brackets
                              : diag::where_inside_brackets;

   auto Diag = diagnose(WhereRangeInsideBrackets.Start, Message);

   Diag.fixItRemoveChars(RemoveWhereRange.getStart(),
                         RemoveWhereRange.getEnd());

   if (Tok.is(tok::kw_where)) {
     Diag.fixItReplace(Tok.getLoc(), WhereClauseText.str());
   } else {
     Diag.fixItInsert(Lexer::getLocForEndOfToken(SourceMgr, PreviousLoc),
                      WhereClauseText.str());
   }
 }

 /// parseGenericWhereClause - Parse a 'where' clause, which places additional
 /// constraints on generic parameters or types based on them.
 ///
 ///   where-clause:
 ///     'where' requirement (',' requirement) *
 ///
 ///   requirement:
 ///     conformance-requirement
 ///     same-type-requirement
 ///
 ///   conformance-requirement:
 ///     type-identifier ':' type-identifier
 ///     type-identifier ':' type-composition
 ///
 ///   same-type-requirement:
 ///     type-identifier '==' type
 ParserStatus Parser::parseGenericWhereClause(
                SourceLoc &WhereLoc,
                SmallVectorImpl<RequirementRepr> &Requirements,
                bool &FirstTypeInComplete,
                bool AllowLayoutConstraints) {
   SyntaxParsingContext ClauseContext(SyntaxContext,
                                      SyntaxKind::GenericWhereClause);
   ParserStatus Status;
   // Parse the 'where'.
   WhereLoc = consumeToken(tok::kw_where);
   FirstTypeInComplete = false;
   SyntaxParsingContext ReqListContext(SyntaxContext,
                                       SyntaxKind::GenericRequirementList);
   bool HasNextReq;
   do {
     SyntaxParsingContext ReqContext(SyntaxContext, SyntaxContextKind::Syntax);
     // Parse the leading type-identifier.
     auto FirstTypeResult = parseTypeIdentifier();
     if (FirstTypeResult.hasSyntax())
       SyntaxContext->addSyntax(FirstTypeResult.getSyntax());
     ParserResult<TypeRepr> FirstType = FirstTypeResult.getASTResult();

     if (FirstType.hasCodeCompletion()) {
       Status.setHasCodeCompletion();
       FirstTypeInComplete = true;
     }

     if (FirstType.isNull()) {
       Status.setIsParseError();
       break;
     }

     if (Tok.is(tok::colon)) {
       // A conformance-requirement.
       SourceLoc ColonLoc = consumeToken();
       ReqContext.setCreateSyntax(SyntaxKind::ConformanceRequirement);
       if (Tok.is(tok::identifier) &&
           getLayoutConstraint(Context.getIdentifier(Tok.getText()), Context)
               ->isKnownLayout()) {
         // Parse a layout constraint.
         auto LayoutName = Context.getIdentifier(Tok.getText());
         auto LayoutLoc = consumeToken();
         auto LayoutInfo = parseLayoutConstraint(LayoutName);
         if (!LayoutInfo->isKnownLayout()) {
           // There was a bug in the layout constraint.
           Status.setIsParseError();
         }
         auto Layout = LayoutInfo;
         // Types in SIL mode may contain layout constraints.
         if (!AllowLayoutConstraints && !isInSILMode()) {
           diagnose(LayoutLoc,
                    diag::layout_constraints_only_inside_specialize_attr);
         } else {
           // Add the layout requirement.
           Requirements.push_back(RequirementRepr::getLayoutConstraint(
               FirstType.get(), ColonLoc,
               LayoutConstraintLoc(Layout, LayoutLoc)));
         }
       } else {
         // Parse the protocol or composition.
         ParserResult<TypeRepr> Protocol = parseType();

         if (Protocol.isNull()) {
           Status.setIsParseError();
           if (Protocol.hasCodeCompletion())
             Status.setHasCodeCompletion();
           break;
         }

         // Add the requirement.
         Requirements.push_back(RequirementRepr::getTypeConstraint(
             FirstType.get(), ColonLoc, Protocol.get()));
       }
     } else if ((Tok.isAnyOperator() && Tok.getText() == "==") ||
                Tok.is(tok::equal)) {
       ReqContext.setCreateSyntax(SyntaxKind::SameTypeRequirement);
       // A same-type-requirement
       if (Tok.is(tok::equal)) {
         diagnose(Tok, diag::requires_single_equal)
           .fixItReplace(SourceRange(Tok.getLoc()), "==");
       }
       SourceLoc EqualLoc = consumeToken();

       // Parse the second type.
       ParserResult<TypeRepr> SecondType = parseType();
       if (SecondType.isNull()) {
         Status.setIsParseError();
         if (SecondType.hasCodeCompletion())
           Status.setHasCodeCompletion();
         break;
       }

       // Add the requirement
       Requirements.push_back(RequirementRepr::getSameType(FirstType.get(),
                                                       EqualLoc,
                                                       SecondType.get()));
     } else {
       diagnose(Tok, diag::expected_requirement_delim);
       Status.setIsParseError();
       break;
     }
     HasNextReq = consumeIf(tok::comma);
     // If there's a comma, keep parsing the list.
   } while (HasNextReq);

   if (Requirements.empty())
     WhereLoc = SourceLoc();

   return Status;
 }


 /// Parse a free-standing where clause attached to a declaration, adding it to
 /// a generic parameter list that may (or may not) already exist.
 ParserStatus Parser::
 parseFreestandingGenericWhereClause(GenericParamList *&genericParams,
                                     WhereClauseKind kind) {
   assert(Tok.is(tok::kw_where) && "Shouldn't call this without a where");

   // Push the generic arguments back into a local scope so that references will
   // find them.
   Scope S(this, ScopeKind::Generics);

   if (genericParams)
     for (auto pd : genericParams->getParams())
       addToScope(pd);

   SmallVector<RequirementRepr, 4> Requirements;
   SourceLoc WhereLoc;
   bool FirstTypeInComplete;
   auto result = parseGenericWhereClause(WhereLoc, Requirements,
                                         FirstTypeInComplete);
   if (result.shouldStopParsing() || Requirements.empty())
     return result;

   if (!genericParams)
     diagnose(WhereLoc, diag::where_without_generic_params, unsigned(kind));
   else
     genericParams->addTrailingWhereClause(Context, WhereLoc, Requirements);
   return ParserStatus();
 }

 /// Parse a where clause after a protocol or associated type declaration.
 ParserStatus Parser::parseProtocolOrAssociatedTypeWhereClause(
     TrailingWhereClause *&trailingWhere, bool isProtocol) {
   assert(Tok.is(tok::kw_where) && "Shouldn't call this without a where");
   SourceLoc whereLoc;
   SmallVector<RequirementRepr, 4> requirements;
   bool firstTypeInComplete;
   auto whereStatus =
       parseGenericWhereClause(whereLoc, requirements, firstTypeInComplete);
   if (whereStatus.isSuccess()) {
     trailingWhere =
         TrailingWhereClause::create(Context, whereLoc, requirements);
   } else if (whereStatus.hasCodeCompletion()) {
     return whereStatus;
   }

   return ParserStatus();
 }
	//===--- ParseGeneric.cpp - Swift Language Parser for Generics ------------===//
	//
	// This source file is part of the Swift.org open source project
	//
	// Copyright (c) 2014 - 2017 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
	//
	//===----------------------------------------------------------------------===//
	//
	// Generic Parsing and AST Building
	//
	//===----------------------------------------------------------------------===//

	#include "swift/Parse/Parser.h"
	#include "swift/AST/DiagnosticsParse.h"
	#include "swift/Parse/CodeCompletionCallbacks.h"
	#include "swift/Parse/Lexer.h"
	#include "swift/Syntax/SyntaxBuilders.h"
	#include "swift/Syntax/SyntaxNodes.h"
	#include "swift/Syntax/SyntaxParsingContext.h"
	using namespace swift;
	using namespace swift::syntax;

	/// parseGenericParameters - Parse a sequence of generic parameters, e.g.,
	/// < T : Comparable, U : Container> along with an optional requires clause.
	///
	/// generic-params:
	/// '<' generic-param (',' generic-param)* where-clause? '>'
	///
	/// generic-param:
	/// identifier
	/// identifier ':' type-identifier
	/// identifier ':' type-composition
	///
	/// When parsing the generic parameters, this routine establishes a new scope
	/// and adds those parameters to the scope.
	ParserResult<GenericParamList> Parser::parseGenericParameters() {
	SyntaxParsingContext GPSContext(SyntaxContext, SyntaxKind::GenericParameterClause);
	// Parse the opening '<'.
	assert(startsWithLess(Tok) && "Generic parameter list must start with '<'");
	return parseGenericParameters(consumeStartingLess());
	}

	ParserStatus
	Parser::parseGenericParametersBeforeWhere(SourceLoc LAngleLoc,
	SmallVectorImpl<GenericTypeParamDecl *> &GenericParams) {
	ParserStatus Result;
	SyntaxParsingContext GPSContext(SyntaxContext, SyntaxKind::GenericParameterList);
	bool HasNextParam;
	do {
	SyntaxParsingContext GParamContext(SyntaxContext, SyntaxKind::GenericParameter);
	// Note that we're parsing a declaration.
	StructureMarkerRAII ParsingDecl(*this, Tok.getLoc(),
	StructureMarkerKind::Declaration);

	// Parse attributes.
	DeclAttributes attributes;
	if (Tok.hasComment())
	attributes.add(new (Context) RawDocCommentAttr(Tok.getCommentRange()));
	bool foundCCTokenInAttr;
	parseDeclAttributeList(attributes, foundCCTokenInAttr);

	// Parse the name of the parameter.
	Identifier Name;
	SourceLoc NameLoc;
	if (parseIdentifier(Name, NameLoc,
	diag::expected_generics_parameter_name)) {
	Result.setIsParseError();
	break;
	}

	// Parse the ':' followed by a type.
	SmallVector<TypeLoc, 1> Inherited;
	if (Tok.is(tok::colon)) {
	(void)consumeToken();
	ParserResult<TypeRepr> Ty;

	if (Tok.isAny(tok::identifier, tok::code_complete, tok::kw_protocol,
	tok::kw_Any)) {
	Ty = parseType();
	} else if (Tok.is(tok::kw_class)) {
	diagnose(Tok, diag::unexpected_class_constraint);
	diagnose(Tok, diag::suggest_anyobject)
	.fixItReplace(Tok.getLoc(), "AnyObject");
	consumeToken();
	Result.setIsParseError();
	} else {
	diagnose(Tok, diag::expected_generics_type_restriction, Name);
	Result.setIsParseError();
	}

	if (Ty.hasCodeCompletion())
	return makeParserCodeCompletionStatus();

	if (Ty.isNonNull())
	Inherited.push_back(Ty.get());
	}

	// We always create generic type parameters with an invalid depth.
	// Semantic analysis fills in the depth when it processes the generic
	// parameter list.
	auto Param = new (Context) GenericTypeParamDecl(CurDeclContext, Name, NameLoc,
	GenericTypeParamDecl::InvalidDepth,
	GenericParams.size());
	if (!Inherited.empty())
	Param->setInherited(Context.AllocateCopy(Inherited));
	GenericParams.push_back(Param);

	// Attach attributes.
	Param->getAttrs() = attributes;

	// Add this parameter to the scope.
	addToScope(Param);

	// Parse the comma, if the list continues.
	HasNextParam = consumeIf(tok::comma);
	} while (HasNextParam);

	return Result;
	}

	ParserResult<GenericParamList>
	Parser::parseGenericParameters(SourceLoc LAngleLoc) {
	// Parse the generic parameter list.
	SmallVector<GenericTypeParamDecl *, 4> GenericParams;
	auto Result = parseGenericParametersBeforeWhere(LAngleLoc, GenericParams);

	// Return early if there was code completion token.
	if (Result.hasCodeCompletion())
	return Result;
	auto Invalid = Result.isError();

	// Parse the optional where-clause.
	SourceLoc WhereLoc;
	SmallVector<RequirementRepr, 4> Requirements;
	bool FirstTypeInComplete;
	if (Tok.is(tok::kw_where) &&
	parseGenericWhereClause(WhereLoc, Requirements,
	FirstTypeInComplete).isError()) {
	Invalid = true;
	}

	// Parse the closing '>'.
	SourceLoc RAngleLoc;
	if (startsWithGreater(Tok)) {
	RAngleLoc = consumeStartingGreater();
	} else {
	if (!Invalid) {
	diagnose(Tok, diag::expected_rangle_generics_param);
	diagnose(LAngleLoc, diag::opening_angle);
	Invalid = true;
	}

	// Skip until we hit the '>'.
	RAngleLoc = skipUntilGreaterInTypeList();
	}

	if (GenericParams.empty())
	return nullptr;

	return makeParserResult(GenericParamList::create(Context, LAngleLoc,
	GenericParams, WhereLoc,
	Requirements, RAngleLoc));
	}

	ParserResult<GenericParamList> Parser::maybeParseGenericParams() {
	if (!startsWithLess(Tok))
	return nullptr;

	if (!isInSILMode())
	return parseGenericParameters();

	// In SIL mode, we can have multiple generic parameter lists, with the
	// first one being the outmost generic parameter list.
	GenericParamList gpl = nullptr, outer_gpl = nullptr;
	do {
	gpl = parseGenericParameters().getPtrOrNull();
	if (!gpl)
	return nullptr;

	if (outer_gpl)
	gpl->setOuterParameters(outer_gpl);
	outer_gpl = gpl;
	} while (startsWithLess(Tok));
	return makeParserResult(gpl);
	}

	void
	Parser::diagnoseWhereClauseInGenericParamList(const GenericParamList *
	GenericParams) {
	if (GenericParams == nullptr \|\| GenericParams->getWhereLoc().isInvalid())
	return;



	auto WhereRangeInsideBrackets = GenericParams->getWhereClauseSourceRange();

	// Move everything immediately following the last generic parameter
	// as written all the way to the right angle bracket (">")
	auto LastGenericParam = GenericParams->getParams().back();
	auto EndOfLastGenericParam =
	Lexer::getLocForEndOfToken(SourceMgr, LastGenericParam->getEndLoc());

	CharSourceRange RemoveWhereRange { SourceMgr,
	EndOfLastGenericParam,
	GenericParams->getRAngleLoc()
	};

	auto WhereCharRange =
	Lexer::getCharSourceRangeFromSourceRange(SourceMgr,
	GenericParams->getWhereClauseSourceRange());

	SmallString<64> Buffer;
	llvm::raw_svector_ostream WhereClauseText(Buffer);
	WhereClauseText << SourceMgr.extractText(Tok.is(tok::kw_where)
	? WhereCharRange
	: RemoveWhereRange);

	// If, for some reason, there was a where clause in both locations, we're
	// adding to the list of requirements, so tack on a comma here before
	// inserting it at the head of the later where clause.
	if (Tok.is(tok::kw_where))
	WhereClauseText << ',';

	// For Swift 3, keep this warning.
	const auto Message = Context.isSwiftVersion3()
	? diag::swift3_where_inside_brackets
	: diag::where_inside_brackets;

	auto Diag = diagnose(WhereRangeInsideBrackets.Start, Message);

	Diag.fixItRemoveChars(RemoveWhereRange.getStart(),
	RemoveWhereRange.getEnd());

	if (Tok.is(tok::kw_where)) {
	Diag.fixItReplace(Tok.getLoc(), WhereClauseText.str());
	} else {
	Diag.fixItInsert(Lexer::getLocForEndOfToken(SourceMgr, PreviousLoc),
	WhereClauseText.str());
	}
	}

	/// parseGenericWhereClause - Parse a 'where' clause, which places additional
	/// constraints on generic parameters or types based on them.
	///
	/// where-clause:
	/// 'where' requirement (',' requirement) *
	///
	/// requirement:
	/// conformance-requirement
	/// same-type-requirement
	///
	/// conformance-requirement:
	/// type-identifier ':' type-identifier
	/// type-identifier ':' type-composition
	///
	/// same-type-requirement:
	/// type-identifier '==' type
	ParserStatus Parser::parseGenericWhereClause(
	SourceLoc &WhereLoc,
	SmallVectorImpl<RequirementRepr> &Requirements,
	bool &FirstTypeInComplete,
	bool AllowLayoutConstraints) {
	SyntaxParsingContext ClauseContext(SyntaxContext,
	SyntaxKind::GenericWhereClause);
	ParserStatus Status;
	// Parse the 'where'.
	WhereLoc = consumeToken(tok::kw_where);
	FirstTypeInComplete = false;
	SyntaxParsingContext ReqListContext(SyntaxContext,
	SyntaxKind::GenericRequirementList);
	bool HasNextReq;
	do {
	SyntaxParsingContext ReqContext(SyntaxContext, SyntaxContextKind::Syntax);
	// Parse the leading type-identifier.
	auto FirstTypeResult = parseTypeIdentifier();
	if (FirstTypeResult.hasSyntax())
	SyntaxContext->addSyntax(FirstTypeResult.getSyntax());
	ParserResult<TypeRepr> FirstType = FirstTypeResult.getASTResult();

	if (FirstType.hasCodeCompletion()) {
	Status.setHasCodeCompletion();
	FirstTypeInComplete = true;
	}

	if (FirstType.isNull()) {
	Status.setIsParseError();
	break;
	}

	if (Tok.is(tok::colon)) {
	// A conformance-requirement.
	SourceLoc ColonLoc = consumeToken();
	ReqContext.setCreateSyntax(SyntaxKind::ConformanceRequirement);
	if (Tok.is(tok::identifier) &&
	getLayoutConstraint(Context.getIdentifier(Tok.getText()), Context)
	->isKnownLayout()) {
	// Parse a layout constraint.
	auto LayoutName = Context.getIdentifier(Tok.getText());
	auto LayoutLoc = consumeToken();
	auto LayoutInfo = parseLayoutConstraint(LayoutName);
	if (!LayoutInfo->isKnownLayout()) {
	// There was a bug in the layout constraint.
	Status.setIsParseError();
	}
	auto Layout = LayoutInfo;
	// Types in SIL mode may contain layout constraints.
	if (!AllowLayoutConstraints && !isInSILMode()) {
	diagnose(LayoutLoc,
	diag::layout_constraints_only_inside_specialize_attr);
	} else {
	// Add the layout requirement.
	Requirements.push_back(RequirementRepr::getLayoutConstraint(
	FirstType.get(), ColonLoc,
	LayoutConstraintLoc(Layout, LayoutLoc)));
	}
	} else {
	// Parse the protocol or composition.
	ParserResult<TypeRepr> Protocol = parseType();

	if (Protocol.isNull()) {
	Status.setIsParseError();
	if (Protocol.hasCodeCompletion())
	Status.setHasCodeCompletion();
	break;
	}

	// Add the requirement.
	Requirements.push_back(RequirementRepr::getTypeConstraint(
	FirstType.get(), ColonLoc, Protocol.get()));
	}
	} else if ((Tok.isAnyOperator() && Tok.getText() == "==") \|\|
	Tok.is(tok::equal)) {
	ReqContext.setCreateSyntax(SyntaxKind::SameTypeRequirement);
	// A same-type-requirement
	if (Tok.is(tok::equal)) {
	diagnose(Tok, diag::requires_single_equal)
	.fixItReplace(SourceRange(Tok.getLoc()), "==");
	}
	SourceLoc EqualLoc = consumeToken();

	// Parse the second type.
	ParserResult<TypeRepr> SecondType = parseType();
	if (SecondType.isNull()) {
	Status.setIsParseError();
	if (SecondType.hasCodeCompletion())
	Status.setHasCodeCompletion();
	break;
	}

	// Add the requirement
	Requirements.push_back(RequirementRepr::getSameType(FirstType.get(),
	EqualLoc,
	SecondType.get()));
	} else {
	diagnose(Tok, diag::expected_requirement_delim);
	Status.setIsParseError();
	break;
	}
	HasNextReq = consumeIf(tok::comma);
	// If there's a comma, keep parsing the list.
	} while (HasNextReq);

	if (Requirements.empty())
	WhereLoc = SourceLoc();

	return Status;
	}


	/// Parse a free-standing where clause attached to a declaration, adding it to
	/// a generic parameter list that may (or may not) already exist.
	ParserStatus Parser::
	parseFreestandingGenericWhereClause(GenericParamList *&genericParams,
	WhereClauseKind kind) {
	assert(Tok.is(tok::kw_where) && "Shouldn't call this without a where");

	// Push the generic arguments back into a local scope so that references will
	// find them.
	Scope S(this, ScopeKind::Generics);

	if (genericParams)
	for (auto pd : genericParams->getParams())
	addToScope(pd);

	SmallVector<RequirementRepr, 4> Requirements;
	SourceLoc WhereLoc;
	bool FirstTypeInComplete;
	auto result = parseGenericWhereClause(WhereLoc, Requirements,
	FirstTypeInComplete);
	if (result.shouldStopParsing() \|\| Requirements.empty())
	return result;

	if (!genericParams)
	diagnose(WhereLoc, diag::where_without_generic_params, unsigned(kind));
	else
	genericParams->addTrailingWhereClause(Context, WhereLoc, Requirements);
	return ParserStatus();
	}

	/// Parse a where clause after a protocol or associated type declaration.
	ParserStatus Parser::parseProtocolOrAssociatedTypeWhereClause(
	TrailingWhereClause *&trailingWhere, bool isProtocol) {
	assert(Tok.is(tok::kw_where) && "Shouldn't call this without a where");
	SourceLoc whereLoc;
	SmallVector<RequirementRepr, 4> requirements;
	bool firstTypeInComplete;
	auto whereStatus =
	parseGenericWhereClause(whereLoc, requirements, firstTypeInComplete);
	if (whereStatus.isSuccess()) {
	trailingWhere =
	TrailingWhereClause::create(Context, whereLoc, requirements);
	} else if (whereStatus.hasCodeCompletion()) {
	return whereStatus;
	}

	return ParserStatus();
	}