go/types, types2: adjust Check.funcInst signature

Per feedback from prior CL.

Change-Id: Icbf6149c3b61e26085caf6f368d22ad4f02c75fd
Reviewed-on: https://go-review.googlesource.com/c/go/+/480316
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/call.go

@@ -15,24 +15,18 @@ import (
 )
 
 // funcInst type-checks a function instantiation and returns the result in x.
-// The incoming x must be an uninstantiated generic function. If inst != 0,
+// The incoming x must be an uninstantiated generic function. If inst != nil,
 // it provides (some or all of) the type arguments (inst.Index) for the
-// instantiation. If the target type T != nil and is a (non-generic) function
-// signature, the signature's parameter types are used to infer additional
-// missing type arguments of x, if any.
-// At least one of inst or T must be provided.
-func (check *Checker) funcInst(T Type, pos syntax.Pos, x *operand, inst *syntax.IndexExpr) {
+// instantiation. If the target type tsig != nil, the signature's parameter
+// types are used to infer additional missing type arguments of x, if any.
+// At least one of tsig or inst must be provided.
+func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst *syntax.IndexExpr) {
+	assert(tsig != nil || inst != nil)
+
 	if !check.allowVersion(check.pkg, 1, 18) {
 		check.versionErrorf(inst.Pos(), "go1.18", "function instantiation")
 	}
 
-	// tsig is the (assignment) target function signature, or nil.
-	// TODO(gri) refactor and pass in tsig to funcInst instead
-	var tsig *Signature
-	if check.conf.EnableReverseTypeInference && T != nil {
-		tsig, _ = under(T).(*Signature)
-	}
-
 	// targs and xlist are the type arguments and corresponding type expressions, or nil.
 	var targs []Type
 	var xlist []syntax.Expr
@@ -47,8 +41,6 @@ func (check *Checker) funcInst(T Type, pos syntax.Pos, x *operand, inst *syntax.
 		assert(len(targs) == len(xlist))
 	}
 
-	assert(tsig != nil || targs != nil)
-
 	// Check the number of type arguments (got) vs number of type parameters (want).
 	// Note that x is a function value, not a type expression, so we don't need to
 	// call under below.

src/cmd/compile/internal/types2/expr.go

@@ -1293,8 +1293,8 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 	case *Signature:
 		if t.tparams != nil {
 			if check.conf.EnableReverseTypeInference && T != nil {
-				if _, ok := under(T).(*Signature); ok {
-					check.funcInst(T, x.Pos(), x, nil)
+				if tsig, _ := under(T).(*Signature); tsig != nil {
+					check.funcInst(tsig, x.Pos(), x, nil)
 					return
 				}
 			}
@@ -1617,7 +1617,11 @@ func (check *Checker) exprInternal(T Type, x *operand, e syntax.Expr, hint Type)
 
 	case *syntax.IndexExpr:
 		if check.indexExpr(x, e) {
-			check.funcInst(T, e.Pos(), x, e)
+			var tsig *Signature
+			if check.conf.EnableReverseTypeInference && T != nil {
+				tsig, _ = under(T).(*Signature)
+			}
+			check.funcInst(tsig, e.Pos(), x, e)
 		}
 		if x.mode == invalid {
 			goto Error

src/go/types/call.go

@@ -17,24 +17,18 @@ import (
 )
 
 // funcInst type-checks a function instantiation and returns the result in x.
-// The incoming x must be an uninstantiated generic function. If ix != 0,
+// The incoming x must be an uninstantiated generic function. If ix != nil,
 // it provides (some or all of) the type arguments (ix.Indices) for the
-// instantiation. If the target type T != nil and is a (non-generic) function
-// signature, the signature's parameter types are used to infer additional
-// missing type arguments of x, if any.
-// At least one of inst or T must be provided.
-func (check *Checker) funcInst(T Type, pos token.Pos, x *operand, ix *typeparams.IndexExpr) {
+// instantiation. If the target type tsig != nil, the signature's parameter
+// types are used to infer additional missing type arguments of x, if any.
+// At least one of tsig or ix must be provided.
+func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *typeparams.IndexExpr) {
+	assert(tsig != nil || ix != nil)
+
 	if !check.allowVersion(check.pkg, 1, 18) {
 		check.softErrorf(inNode(ix.Orig, ix.Lbrack), UnsupportedFeature, "function instantiation requires go1.18 or later")
 	}
 
-	// tsig is the (assignment) target function signature, or nil.
-	// TODO(gri) refactor and pass in tsig to funcInst instead
-	var tsig *Signature
-	if check.conf._EnableReverseTypeInference && T != nil {
-		tsig, _ = under(T).(*Signature)
-	}
-
 	// targs and xlist are the type arguments and corresponding type expressions, or nil.
 	var targs []Type
 	var xlist []ast.Expr
@@ -49,8 +43,6 @@ func (check *Checker) funcInst(T Type, pos token.Pos, x *operand, ix *typeparams
 		assert(len(targs) == len(xlist))
 	}
 
-	assert(tsig != nil || targs != nil)
-
 	// Check the number of type arguments (got) vs number of type parameters (want).
 	// Note that x is a function value, not a type expression, so we don't need to
 	// call under below.

src/go/types/expr.go

@@ -1278,8 +1278,8 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 	case *Signature:
 		if t.tparams != nil {
 			if check.conf._EnableReverseTypeInference && T != nil {
-				if _, ok := under(T).(*Signature); ok {
-					check.funcInst(T, x.Pos(), x, nil)
+				if tsig, _ := under(T).(*Signature); tsig != nil {
+					check.funcInst(tsig, x.Pos(), x, nil)
 					return
 				}
 			}
@@ -1600,7 +1600,11 @@ func (check *Checker) exprInternal(T Type, x *operand, e ast.Expr, hint Type) ex
 	case *ast.IndexExpr, *ast.IndexListExpr:
 		ix := typeparams.UnpackIndexExpr(e)
 		if check.indexExpr(x, ix) {
-			check.funcInst(T, e.Pos(), x, ix)
+			var tsig *Signature
+			if check.conf._EnableReverseTypeInference && T != nil {
+				tsig, _ = under(T).(*Signature)
+			}
+			check.funcInst(tsig, e.Pos(), x, ix)
 		}
 		if x.mode == invalid {
 			goto Error