// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package types

import (
	
	
	
	. 
)

// ----------------------------------------------------------------------------
// API

// A Signature represents a (non-builtin) function or method type.
// The receiver is ignored when comparing signatures for identity.
type Signature struct {
	// We need to keep the scope in Signature (rather than passing it around
	// and store it in the Func Object) because when type-checking a function
	// literal we call the general type checker which returns a general Type.
	// We then unpack the *Signature and use the scope for the literal body.
	rparams  *TypeParamList // receiver type parameters from left to right, or nil
	tparams  *TypeParamList // type parameters from left to right, or nil
	scope    *Scope         // function scope for package-local and non-instantiated signatures; nil otherwise
	recv     *Var           // nil if not a method
	params   *Tuple         // (incoming) parameters from left to right; or nil
	results  *Tuple         // (outgoing) results from left to right; or nil
	variadic bool           // true if the last parameter's type is of the form ...T (or string, for append built-in only)
}

// NewSignature returns a new function type for the given receiver, parameters,
// and results, either of which may be nil. If variadic is set, the function
// is variadic, it must have at least one parameter, and the last parameter
// must be of unnamed slice type.
//
// Deprecated: Use [NewSignatureType] instead which allows for type parameters.
func ( *Var, ,  *Tuple,  bool) *Signature {
	return NewSignatureType(, nil, nil, , , )
}

// NewSignatureType creates a new function type for the given receiver,
// receiver type parameters, type parameters, parameters, and results. If
// variadic is set, params must hold at least one parameter and the last
// parameter's core type must be of unnamed slice or bytestring type.
// If recv is non-nil, typeParams must be empty. If recvTypeParams is
// non-empty, recv must be non-nil.
func ( *Var, ,  []*TypeParam, ,  *Tuple,  bool) *Signature {
	if  {
		 := .Len()
		if  == 0 {
			panic("variadic function must have at least one parameter")
		}
		 := coreString(.At( - 1).typ)
		if ,  := .(*Slice); ! && !isString() {
			panic(fmt.Sprintf("got %s, want variadic parameter with unnamed slice type or string as core type", .String()))
		}
	}
	 := &Signature{recv: , params: , results: , variadic: }
	if len() != 0 {
		if  == nil {
			panic("function with receiver type parameters must have a receiver")
		}
		.rparams = bindTParams()
	}
	if len() != 0 {
		if  != nil {
			panic("function with type parameters cannot have a receiver")
		}
		.tparams = bindTParams()
	}
	return 
}

// Recv returns the receiver of signature s (if a method), or nil if a
// function. It is ignored when comparing signatures for identity.
//
// For an abstract method, Recv returns the enclosing interface either
// as a *[Named] or an *[Interface]. Due to embedding, an interface may
// contain methods whose receiver type is a different interface.
func ( *Signature) () *Var { return .recv }

// TypeParams returns the type parameters of signature s, or nil.
func ( *Signature) () *TypeParamList { return .tparams }

// RecvTypeParams returns the receiver type parameters of signature s, or nil.
func ( *Signature) () *TypeParamList { return .rparams }

// Params returns the parameters of signature s, or nil.
func ( *Signature) () *Tuple { return .params }

// Results returns the results of signature s, or nil.
func ( *Signature) () *Tuple { return .results }

// Variadic reports whether the signature s is variadic.
func ( *Signature) () bool { return .variadic }

func ( *Signature) () Type { return  }
func ( *Signature) () string   { return TypeString(, nil) }

// ----------------------------------------------------------------------------
// Implementation

// funcType type-checks a function or method type.
func ( *Checker) ( *Signature,  *ast.FieldList,  *ast.FuncType) {
	.openScope(, "function")
	.scope.isFunc = true
	.recordScope(, .scope)
	.scope = .scope
	defer .closeScope()

	if  != nil && len(.List) > 0 {
		// collect generic receiver type parameters, if any
		// - a receiver type parameter is like any other type parameter, except that it is declared implicitly
		// - the receiver specification acts as local declaration for its type parameters, which may be blank
		, ,  := .unpackRecv(.List[0].Type, true)
		if len() > 0 {
			// The scope of the type parameter T in "func (r T[T]) f()"
			// starts after f, not at "r"; see #52038.
			 := .Params.Pos()
			 := .declareTypeParams(nil, , )
			.rparams = bindTParams()
			// Blank identifiers don't get declared, so naive type-checking of the
			// receiver type expression would fail in Checker.collectParams below,
			// when Checker.ident cannot resolve the _ to a type.
			//
			// Checker.recvTParamMap maps these blank identifiers to their type parameter
			// types, so that they may be resolved in Checker.ident when they fail
			// lookup in the scope.
			for ,  := range  {
				if .Name == "_" {
					if .recvTParamMap == nil {
						.recvTParamMap = make(map[*ast.Ident]*TypeParam)
					}
					.recvTParamMap[] = []
				}
			}
			// determine receiver type to get its type parameters
			// and the respective type parameter bounds
			var  []*TypeParam
			if  != nil {
				// recv should be a Named type (otherwise an error is reported elsewhere)
				// Also: Don't report an error via genericType since it will be reported
				//       again when we type-check the signature.
				// TODO(gri) maybe the receiver should be marked as invalid instead?
				if  := asNamed(.genericType(, nil));  != nil {
					 = .TypeParams().list()
				}
			}
			// provide type parameter bounds
			if len() == len() {
				 := makeRenameMap(, )
				for ,  := range  {
					 := []
					.mono.recordCanon(, )
					// recvTPar.bound is (possibly) parameterized in the context of the
					// receiver type declaration. Substitute parameters for the current
					// context.
					.bound = .subst(.obj.pos, .bound, , nil, .context())
				}
			} else if len() < len() {
				// Reporting an error here is a stop-gap measure to avoid crashes in the
				// compiler when a type parameter/argument cannot be inferred later. It
				// may lead to follow-on errors (see issues go.dev/issue/51339, go.dev/issue/51343).
				// TODO(gri) find a better solution
				 := measure(len(), "type parameter")
				.errorf(, BadRecv, "got %s, but receiver base type declares %d", , len())
			}
		}
	}

	if .TypeParams != nil {
		.collectTypeParams(&.tparams, .TypeParams)
		// Always type-check method type parameters but complain that they are not allowed.
		// (A separate check is needed when type-checking interface method signatures because
		// they don't have a receiver specification.)
		if  != nil {
			.error(.TypeParams, InvalidMethodTypeParams, "methods cannot have type parameters")
		}
	}

	// Use a temporary scope for all parameter declarations and then
	// squash that scope into the parent scope (and report any
	// redeclarations at that time).
	//
	// TODO(adonovan): now that each declaration has the correct
	// scopePos, there should be no need for scope squashing.
	// Audit to ensure all lookups honor scopePos and simplify.
	 := NewScope(.scope, nopos, nopos, "function body (temp. scope)")
	 := .End() // all parameters' scopes start after the signature
	,  := .collectParams(, , false, )
	,  := .collectParams(, .Params, true, )
	,  := .collectParams(, .Results, false, )
	.squash(func(,  Object) {
		 := .newError(DuplicateDecl)
		.addf(, "%s redeclared in this block", .Name())
		.addAltDecl()
		.report()
	})

	if  != nil {
		// recv parameter list present (may be empty)
		// spec: "The receiver is specified via an extra parameter section preceding the
		// method name. That parameter section must declare a single parameter, the receiver."
		var  *Var
		switch len() {
		case 0:
			// error reported by resolver
			 = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
		default:
			// more than one receiver
			.error([len()-1], InvalidRecv, "method has multiple receivers")
			fallthrough // continue with first receiver
		case 1:
			 = [0]
		}
		.recv = 

		// Delay validation of receiver type as it may cause premature expansion
		// of types the receiver type is dependent on (see issues go.dev/issue/51232, go.dev/issue/51233).
		.later(func() {
			// spec: "The receiver type must be of the form T or *T where T is a type name."
			,  := deref(.typ)
			 := Unalias()
			if !isValid() {
				return // error was reported before
			}
			// spec: "The type denoted by T is called the receiver base type; it must not
			// be a pointer or interface type and it must be declared in the same package
			// as the method."
			switch T := .(type) {
			case *Named:
				// The receiver type may be an instantiated type referred to
				// by an alias (which cannot have receiver parameters for now).
				if .TypeArgs() != nil && .RecvTypeParams() == nil {
					.errorf(, InvalidRecv, "cannot define new methods on instantiated type %s", )
					break
				}
				if .obj.pkg != .pkg {
					.errorf(, InvalidRecv, "cannot define new methods on non-local type %s", )
					break
				}
				var  string
				switch u := .under().(type) {
				case *Basic:
					// unsafe.Pointer is treated like a regular pointer
					if .kind == UnsafePointer {
						 = "unsafe.Pointer"
					}
				case *Pointer, *Interface:
					 = "pointer or interface type"
				case *TypeParam:
					// The underlying type of a receiver base type cannot be a
					// type parameter: "type T[P any] P" is not a valid declaration.
					panic("unreachable")
				}
				if  != "" {
					.errorf(, InvalidRecv, "invalid receiver type %s (%s)", , )
				}
			case *Basic:
				.errorf(, InvalidRecv, "cannot define new methods on non-local type %s", )
			default:
				.errorf(, InvalidRecv, "invalid receiver type %s", .typ)
			}
		}).describef(, "validate receiver %s", )
	}

	.params = NewTuple(...)
	.results = NewTuple(...)
	.variadic = 
}

// collectParams declares the parameters of list in scope and returns the corresponding
// variable list.
func ( *Checker) ( *Scope,  *ast.FieldList,  bool,  token.Pos) ( []*Var,  bool) {
	if  == nil {
		return
	}

	var ,  bool
	for ,  := range .List {
		 := .Type
		if ,  := .(*ast.Ellipsis);  != nil {
			 = .Elt
			if  &&  == len(.List)-1 && len(.Names) <= 1 {
				 = true
			} else {
				.softErrorf(, MisplacedDotDotDot, "can only use ... with final parameter in list")
				// ignore ... and continue
			}
		}
		 := .varType()
		// The parser ensures that f.Tag is nil and we don't
		// care if a constructed AST contains a non-nil tag.
		if len(.Names) > 0 {
			// named parameter
			for ,  := range .Names {
				if .Name == "" {
					.error(, InvalidSyntaxTree, "anonymous parameter")
					// ok to continue
				}
				 := NewParam(.Pos(), .pkg, .Name, )
				.declare(, , , )
				 = append(, )
			}
			 = true
		} else {
			// anonymous parameter
			 := NewParam(.Pos(), .pkg, "", )
			.recordImplicit(, )
			 = append(, )
			 = true
		}
	}

	if  &&  {
		.error(, InvalidSyntaxTree, "list contains both named and anonymous parameters")
		// ok to continue
	}

	// For a variadic function, change the last parameter's type from T to []T.
	// Since we type-checked T rather than ...T, we also need to retro-actively
	// record the type for ...T.
	if  {
		 := [len()-1]
		.typ = &Slice{elem: .typ}
		.recordTypeAndValue(.List[len(.List)-1].Type, typexpr, .typ, nil)
	}

	return
}