[dev.typeparams] cmd/compile/internal/types2: move instantiation code to instantiate.go (cleanup)

No code changes besides moving the two functions and updating a
couple of file comments.

Change-Id: I13a6a78b6e8c132c20c7f81a329f31d5edab0453
Reviewed-on: https://go-review.googlesource.com/c/go/+/333589
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 1 insertions, 183 deletions

diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 32cf527372..63b234a60e 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -2,9 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file implements instantiation of generic types
-// through substitution of type parameters by actual
-// types.
+// This file implements type parameter substitution.
 
 package types2
 
@@ -53,186 +51,6 @@ func (m *substMap) lookup(tpar *TypeParam) Type {
 	return tpar
 }
 
-// Instantiate instantiates the type typ with the given type arguments
-// targs. To check type constraint satisfaction, verify must be set.
-// pos and posList correspond to the instantiation and type argument
-// positions respectively; posList may be nil or shorter than the number
-// of type arguments provided.
-// typ must be a *Named or a *Signature type, and its number of type
-// parameters must match the number of provided type arguments.
-// The receiver (check) may be nil if and only if verify is not set.
-// The result is a new, instantiated (not generic) type of the same kind
-// (either a *Named or a *Signature).
-// Any methods attached to a *Named are simply copied; they are not
-// instantiated.
-func (check *Checker) Instantiate(pos syntax.Pos, typ Type, targs []Type, posList []syntax.Pos, verify bool) (res Type) {
-	if verify && check == nil {
-		panic("cannot have nil receiver if verify is set")
-	}
-
-	if check != nil && check.conf.Trace {
-		check.trace(pos, "-- instantiating %s with %s", typ, typeListString(targs))
-		check.indent++
-		defer func() {
-			check.indent--
-			var under Type
-			if res != nil {
-				// Calling under() here may lead to endless instantiations.
-				// Test case: type T[P any] T[P]
-				// TODO(gri) investigate if that's a bug or to be expected.
-				under = res.Underlying()
-			}
-			check.trace(pos, "=> %s (under = %s)", res, under)
-		}()
-	}
-
-	assert(len(posList) <= len(targs))
-
-	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
-	var tparams []*TypeName
-	switch t := typ.(type) {
-	case *Named:
-		tparams = t.TParams()
-	case *Signature:
-		tparams = t.tparams
-		defer func() {
-			// If we had an unexpected failure somewhere don't panic below when
-			// asserting res.(*Signature). Check for *Signature in case Typ[Invalid]
-			// is returned.
-			if _, ok := res.(*Signature); !ok {
-				return
-			}
-			// If the signature doesn't use its type parameters, subst
-			// will not make a copy. In that case, make a copy now (so
-			// we can set tparams to nil w/o causing side-effects).
-			if t == res {
-				copy := *t
-				res = &copy
-			}
-			// After instantiating a generic signature, it is not generic
-			// anymore; we need to set tparams to nil.
-			res.(*Signature).tparams = nil
-		}()
-	default:
-		// only types and functions can be generic
-		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
-	}
-
-	// the number of supplied types must match the number of type parameters
-	if len(targs) != len(tparams) {
-		// TODO(gri) provide better error message
-		if check != nil {
-			check.errorf(pos, "got %d arguments but %d type parameters", len(targs), len(tparams))
-			return Typ[Invalid]
-		}
-		panic(fmt.Sprintf("%v: got %d arguments but %d type parameters", pos, len(targs), len(tparams)))
-	}
-
-	if len(tparams) == 0 {
-		return typ // nothing to do (minor optimization)
-	}
-
-	smap := makeSubstMap(tparams, targs)
-
-	// check bounds
-	if verify {
-		for i, tname := range tparams {
-			// best position for error reporting
-			pos := pos
-			if i < len(posList) {
-				pos = posList[i]
-			}
-			// stop checking bounds after the first failure
-			if !check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap) {
-				break
-			}
-		}
-	}
-
-	return check.subst(pos, typ, smap)
-}
-
-// satisfies reports whether the type argument targ satisfies the constraint of type parameter
-// parameter tpar (after any of its type parameters have been substituted through smap).
-// A suitable error is reported if the result is false.
-// TODO(gri) This should be a method of interfaces or type sets.
-func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap *substMap) bool {
-	iface := tpar.Bound()
-	if iface.Empty() {
-		return true // no type bound
-	}
-
-	// The type parameter bound is parameterized with the same type parameters
-	// as the instantiated type; before we can use it for bounds checking we
-	// need to instantiate it with the type arguments with which we instantiate
-	// the parameterized type.
-	iface = check.subst(pos, iface, smap).(*Interface)
-
-	// targ must implement iface (methods)
-	// - check only if we have methods
-	if iface.NumMethods() > 0 {
-		// If the type argument is a pointer to a type parameter, the type argument's
-		// method set is empty.
-		// TODO(gri) is this what we want? (spec question)
-		if base, isPtr := deref(targ); isPtr && asTypeParam(base) != nil {
-			check.errorf(pos, "%s has no methods", targ)
-			return false
-		}
-		if m, wrong := check.missingMethod(targ, iface, true); m != nil {
-			// TODO(gri) needs to print updated name to avoid major confusion in error message!
-			//           (print warning for now)
-			// Old warning:
-			// check.softErrorf(pos, "%s does not satisfy %s (warning: name not updated) = %s (missing method %s)", targ, tpar.bound, iface, m)
-			if m.name == "==" {
-				// We don't want to report "missing method ==".
-				check.softErrorf(pos, "%s does not satisfy comparable", targ)
-			} else if wrong != nil {
-				// TODO(gri) This can still report uninstantiated types which makes the error message
-				//           more difficult to read then necessary.
-				check.softErrorf(pos,
-					"%s does not satisfy %s: wrong method signature\n\tgot  %s\n\twant %s",
-					targ, tpar.bound, wrong, m,
-				)
-			} else {
-				check.softErrorf(pos, "%s does not satisfy %s (missing method %s)", targ, tpar.bound, m.name)
-			}
-			return false
-		}
-	}
-
-	// targ's underlying type must also be one of the interface types listed, if any
-	if iface.typeSet().types == nil {
-		return true // nothing to do
-	}
-
-	// If targ is itself a type parameter, each of its possible types, but at least one, must be in the
-	// list of iface types (i.e., the targ type list must be a non-empty subset of the iface types).
-	if targ := asTypeParam(targ); targ != nil {
-		targBound := targ.Bound()
-		if targBound.typeSet().types == nil {
-			check.softErrorf(pos, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
-			return false
-		}
-		return iface.is(func(typ Type, tilde bool) bool {
-			// TODO(gri) incorporate tilde information!
-			if !iface.isSatisfiedBy(typ) {
-				// TODO(gri) match this error message with the one below (or vice versa)
-				check.softErrorf(pos, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, typ, iface.typeSet().types)
-				return false
-			}
-			return true
-		})
-	}
-
-	// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
-	if !iface.isSatisfiedBy(targ) {
-		check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, targ, iface.typeSet().types)
-		return false
-	}
-
-	return true
-}
-
 // subst returns the type typ with its type parameters tpars replaced by
 // the corresponding type arguments targs, recursively.
 // subst is functional in the sense that it doesn't modify the incoming