[dev.typeparams] cmd/compile/internal/types2: move signature checking into separate file

This only moves functionality from one file into another.
Except for import adjustments there are no changes to the
code.

Change-Id: Id0d20a7537f20abe3a257ad3f550b0cb4499598c
Reviewed-on: https://go-review.googlesource.com/c/go/+/321590
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 314 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/signature.go b/src/cmd/compile/internal/types2/signature.go
new file mode 100644
index 0000000000..c8c4cca0a7
--- /dev/null
+++ b/src/cmd/compile/internal/types2/signature.go
@@ -0,0 +1,314 @@
+// 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 types2
+
+import (
+	"cmd/compile/internal/syntax"
+	"fmt"
+)
+
+// Disabled by default, but enabled when running tests (via types_test.go).
+var acceptMethodTypeParams bool
+
+// funcType type-checks a function or method type.
+func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
+	check.openScope(ftyp, "function")
+	check.scope.isFunc = true
+	check.recordScope(ftyp, check.scope)
+	sig.scope = check.scope
+	defer check.closeScope()
+
+	var recvTyp syntax.Expr // rewritten receiver type; valid if != nil
+	if recvPar != nil {
+		// 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
+		_, rname, rparams := check.unpackRecv(recvPar.Type, true)
+		if len(rparams) > 0 {
+			// Blank identifiers don't get declared and regular type-checking of the instantiated
+			// parameterized receiver type expression fails in Checker.collectParams of receiver.
+			// Identify blank type parameters and substitute each with a unique new identifier named
+			// "n_" (where n is the parameter index) and which cannot conflict with any user-defined
+			// name.
+			var smap map[*syntax.Name]*syntax.Name // substitution map from "_" to "!n" identifiers
+			for i, p := range rparams {
+				if p.Value == "_" {
+					new := *p
+					new.Value = fmt.Sprintf("%d_", i)
+					rparams[i] = &new // use n_ identifier instead of _ so it can be looked up
+					if smap == nil {
+						smap = make(map[*syntax.Name]*syntax.Name)
+					}
+					smap[p] = &new
+				}
+			}
+			if smap != nil {
+				// blank identifiers were found => use rewritten receiver type
+				recvTyp = isubst(recvPar.Type, smap)
+			}
+			// TODO(gri) rework declareTypeParams
+			sig.rparams = nil
+			for _, rparam := range rparams {
+				sig.rparams = check.declareTypeParam(sig.rparams, rparam)
+			}
+			// determine receiver type to get its type parameters
+			// and the respective type parameter bounds
+			var recvTParams []*TypeName
+			if rname != 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 recv := asNamed(check.genericType(rname, false)); recv != nil {
+					recvTParams = recv.tparams
+				}
+			}
+			// provide type parameter bounds
+			// - only do this if we have the right number (otherwise an error is reported elsewhere)
+			if len(sig.rparams) == len(recvTParams) {
+				// We have a list of *TypeNames but we need a list of Types.
+				list := make([]Type, len(sig.rparams))
+				for i, t := range sig.rparams {
+					list[i] = t.typ
+				}
+				smap := makeSubstMap(recvTParams, list)
+				for i, tname := range sig.rparams {
+					bound := recvTParams[i].typ.(*TypeParam).bound
+					// bound is (possibly) parameterized in the context of the
+					// receiver type declaration. Substitute parameters for the
+					// current context.
+					// TODO(gri) should we assume now that bounds always exist?
+					//           (no bound == empty interface)
+					if bound != nil {
+						bound = check.subst(tname.pos, bound, smap)
+						tname.typ.(*TypeParam).bound = bound
+					}
+				}
+			}
+		}
+	}
+
+	if tparams != nil {
+		sig.tparams = check.collectTypeParams(tparams)
+		// Always type-check method type parameters but complain if they are not enabled.
+		// (A separate check is needed when type-checking interface method signatures because
+		// they don't have a receiver specification.)
+		if recvPar != nil && !acceptMethodTypeParams {
+			check.error(ftyp, "methods cannot have type parameters")
+		}
+	}
+
+	// Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
+	// declarations and then squash that scope into the parent scope (and report any redeclarations at
+	// that time).
+	scope := NewScope(check.scope, nopos, nopos, "function body (temp. scope)")
+	var recvList []*Var // TODO(gri) remove the need for making a list here
+	if recvPar != nil {
+		recvList, _ = check.collectParams(scope, []*syntax.Field{recvPar}, recvTyp, false) // use rewritten receiver type, if any
+	}
+	params, variadic := check.collectParams(scope, ftyp.ParamList, nil, true)
+	results, _ := check.collectParams(scope, ftyp.ResultList, nil, false)
+	scope.Squash(func(obj, alt Object) {
+		var err error_
+		err.errorf(obj, "%s redeclared in this block", obj.Name())
+		err.recordAltDecl(alt)
+		check.report(&err)
+	})
+
+	if recvPar != 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 recv *Var
+		switch len(recvList) {
+		case 0:
+			// error reported by resolver
+			recv = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
+		default:
+			// more than one receiver
+			check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
+			fallthrough // continue with first receiver
+		case 1:
+			recv = recvList[0]
+		}
+
+		// TODO(gri) We should delay rtyp expansion to when we actually need the
+		//           receiver; thus all checks here should be delayed to later.
+		rtyp, _ := deref(recv.typ)
+		rtyp = expand(rtyp)
+
+		// spec: "The receiver type must be of the form T or *T where T is a type name."
+		// (ignore invalid types - error was reported before)
+		if t := rtyp; t != Typ[Invalid] {
+			var err string
+			if T := asNamed(t); T != nil {
+				// 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."
+				if T.obj.pkg != check.pkg {
+					err = "type not defined in this package"
+					if check.conf.CompilerErrorMessages {
+						check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
+						err = ""
+					}
+				} else {
+					switch u := optype(T).(type) {
+					case *Basic:
+						// unsafe.Pointer is treated like a regular pointer
+						if u.kind == UnsafePointer {
+							err = "unsafe.Pointer"
+						}
+					case *Pointer, *Interface:
+						err = "pointer or interface type"
+					}
+				}
+			} else if T := asBasic(t); T != nil {
+				err = "basic or unnamed type"
+				if check.conf.CompilerErrorMessages {
+					check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
+					err = ""
+				}
+			} else {
+				check.errorf(recv.pos, "invalid receiver type %s", recv.typ)
+			}
+			if err != "" {
+				check.errorf(recv.pos, "invalid receiver type %s (%s)", recv.typ, err)
+				// ok to continue
+			}
+		}
+		sig.recv = recv
+	}
+
+	sig.params = NewTuple(params...)
+	sig.results = NewTuple(results...)
+	sig.variadic = variadic
+}
+
+// collectParams declares the parameters of list in scope and returns the corresponding
+// variable list. If type0 != nil, it is used instead of the first type in list.
+func (check *Checker) collectParams(scope *Scope, list []*syntax.Field, type0 syntax.Expr, variadicOk bool) (params []*Var, variadic bool) {
+	if list == nil {
+		return
+	}
+
+	var named, anonymous bool
+
+	var typ Type
+	var prev syntax.Expr
+	for i, field := range list {
+		ftype := field.Type
+		// type-check type of grouped fields only once
+		if ftype != prev {
+			prev = ftype
+			if i == 0 && type0 != nil {
+				ftype = type0
+			}
+			if t, _ := ftype.(*syntax.DotsType); t != nil {
+				ftype = t.Elem
+				if variadicOk && i == len(list)-1 {
+					variadic = true
+				} else {
+					check.softErrorf(t, "can only use ... with final parameter in list")
+					// ignore ... and continue
+				}
+			}
+			typ = check.varType(ftype)
+		}
+		// The parser ensures that f.Tag is nil and we don't
+		// care if a constructed AST contains a non-nil tag.
+		if field.Name != nil {
+			// named parameter
+			name := field.Name.Value
+			if name == "" {
+				check.error(field.Name, invalidAST+"anonymous parameter")
+				// ok to continue
+			}
+			par := NewParam(field.Name.Pos(), check.pkg, name, typ)
+			check.declare(scope, field.Name, par, scope.pos)
+			params = append(params, par)
+			named = true
+		} else {
+			// anonymous parameter
+			par := NewParam(field.Pos(), check.pkg, "", typ)
+			check.recordImplicit(field, par)
+			params = append(params, par)
+			anonymous = true
+		}
+	}
+
+	if named && anonymous {
+		check.error(list[0], invalidAST+"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 variadic {
+		last := params[len(params)-1]
+		last.typ = &Slice{elem: last.typ}
+		check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)
+	}
+
+	return
+}
+
+// isubst returns an x with identifiers substituted per the substitution map smap.
+// isubst only handles the case of (valid) method receiver type expressions correctly.
+func isubst(x syntax.Expr, smap map[*syntax.Name]*syntax.Name) syntax.Expr {
+	switch n := x.(type) {
+	case *syntax.Name:
+		if alt := smap[n]; alt != nil {
+			return alt
+		}
+	// case *syntax.StarExpr:
+	// 	X := isubst(n.X, smap)
+	// 	if X != n.X {
+	// 		new := *n
+	// 		new.X = X
+	// 		return &new
+	// 	}
+	case *syntax.Operation:
+		if n.Op == syntax.Mul && n.Y == nil {
+			X := isubst(n.X, smap)
+			if X != n.X {
+				new := *n
+				new.X = X
+				return &new
+			}
+		}
+	case *syntax.IndexExpr:
+		Index := isubst(n.Index, smap)
+		if Index != n.Index {
+			new := *n
+			new.Index = Index
+			return &new
+		}
+	case *syntax.ListExpr:
+		var elems []syntax.Expr
+		for i, elem := range n.ElemList {
+			new := isubst(elem, smap)
+			if new != elem {
+				if elems == nil {
+					elems = make([]syntax.Expr, len(n.ElemList))
+					copy(elems, n.ElemList)
+				}
+				elems[i] = new
+			}
+		}
+		if elems != nil {
+			new := *n
+			new.ElemList = elems
+			return &new
+		}
+	case *syntax.ParenExpr:
+		return isubst(n.X, smap) // no need to keep parentheses
+	default:
+		// Other receiver type expressions are invalid.
+		// It's fine to ignore those here as they will
+		// be checked elsewhere.
+	}
+	return x
+}