go/types: split out function instantiation from index expr

This is a port of CL 308371 to go/types. The only meaningful change from
that CL is to use explicit return values in Checker.indexExpr, which I
felt was more readable. I made the same change in types2 to keep them in
sync

Change-Id: I3380c03fe49d3bf4167cadad305abe942785af19
Reviewed-on: https://go-review.googlesource.com/c/go/+/314432
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -20,7 +20,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 	switch x.mode {
 	case invalid:
 		check.use(e.Index)
-		return
+		return false
 
 	case typexpr:
 		// type instantiation
@@ -29,7 +29,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 		if x.typ != Typ[Invalid] {
 			x.mode = typexpr
 		}
-		return
+		return false
 
 	case value:
 		if sig := asSignature(x.typ); sig != nil && len(sig.tparams) > 0 {
@@ -196,7 +196,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 	}
 
 	check.index(index, length)
-	return
+	return false
 }
 
 func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {

src/go/types/call.go

@@ -14,7 +14,7 @@ import (
 	"unicode"
 )
 
-// funcInst type-checks a function instantiaton inst and returns the result in x.
+// funcInst type-checks a function instantiation inst and returns the result in x.
 // The operand x must be the evaluation of inst.X and its type must be a signature.
 func (check *Checker) funcInst(x *operand, inst *ast.IndexExpr) {
 	xlist := typeparams.UnpackExpr(inst.Index)
@@ -71,8 +71,16 @@ func (check *Checker) funcInst(x *operand, inst *ast.IndexExpr) {
 	x.expr = inst
 }
 
-func (check *Checker) call(x *operand, call *ast.CallExpr) exprKind {
+func (check *Checker) callExpr(x *operand, call *ast.CallExpr) exprKind {
+	if iexpr, _ := call.Fun.(*ast.IndexExpr); iexpr != nil {
+		if check.indexExpr(x, iexpr) {
+			check.funcInst(x, iexpr)
+		}
+		x.expr = iexpr
+		check.record(x)
+	} else {
 		check.exprOrType(x, call.Fun)
+	}
 
 	switch x.mode {
 	case invalid:
@@ -121,9 +129,9 @@ func (check *Checker) call(x *operand, call *ast.CallExpr) exprKind {
 			check.hasCallOrRecv = true
 		}
 		return predeclaredFuncs[id].kind
+	}
 
-	default:
-		// function/method call
+	// ordinary function/method call
 	cgocall := x.mode == cgofunc
 
 	sig := asSignature(x.typ)
@@ -164,7 +172,6 @@ func (check *Checker) call(x *operand, call *ast.CallExpr) exprKind {
 
 	return statement
 }
-}
 
 func (check *Checker) exprList(elist []ast.Expr, allowCommaOk bool) (xlist []*operand, commaOk bool) {
 	switch len(elist) {

src/go/types/check.go

@@ -308,6 +308,33 @@ func (check *Checker) processDelayed(top int) {
 	check.delayed = check.delayed[:top]
 }
 
+func (check *Checker) record(x *operand) {
+	// convert x into a user-friendly set of values
+	// TODO(gri) this code can be simplified
+	var typ Type
+	var val constant.Value
+	switch x.mode {
+	case invalid:
+		typ = Typ[Invalid]
+	case novalue:
+		typ = (*Tuple)(nil)
+	case constant_:
+		typ = x.typ
+		val = x.val
+	default:
+		typ = x.typ
+	}
+	assert(x.expr != nil && typ != nil)
+
+	if isUntyped(typ) {
+		// delay type and value recording until we know the type
+		// or until the end of type checking
+		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
+	} else {
+		check.recordTypeAndValue(x.expr, x.mode, typ, val)
+	}
+}
+
 func (check *Checker) recordUntyped() {
 	if !debug && check.Types == nil {
 		return // nothing to do

src/go/types/expr.go

@@ -1027,31 +1027,7 @@ func (check *Checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
 	}
 
 	kind := check.exprInternal(x, e, hint)
-
-	// convert x into a user-friendly set of values
-	// TODO(gri) this code can be simplified
-	var typ Type
-	var val constant.Value
-	switch x.mode {
-	case invalid:
-		typ = Typ[Invalid]
-	case novalue:
-		typ = (*Tuple)(nil)
-	case constant_:
-		typ = x.typ
-		val = x.val
-	default:
-		typ = x.typ
-	}
-	assert(x.expr != nil && typ != nil)
-
-	if isUntyped(typ) {
-		// delay type and value recording until we know the type
-		// or until the end of type checking
-		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
-	} else {
-		check.recordTypeAndValue(e, x.mode, typ, val)
-	}
+	check.record(x)
 
 	return kind
 }
@@ -1340,7 +1316,9 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 		check.selector(x, e)
 
 	case *ast.IndexExpr:
-		check.indexExpr(x, e)
+		if check.indexExpr(x, e) {
+			check.funcInst(x, e)
+		}
 		if x.mode == invalid {
 			goto Error
 		}
@@ -1378,7 +1356,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 		x.typ = T
 
 	case *ast.CallExpr:
-		return check.call(x, e)
+		return check.callExpr(x, e)
 
 	case *ast.StarExpr:
 		check.exprOrType(x, e.X)

src/go/types/index.go

@@ -12,27 +12,30 @@ import (
 	"go/internal/typeparams"
 )
 
-func (check *Checker) indexExpr(x *operand, e *ast.IndexExpr) {
+// If e is a valid function instantiation, indexExpr returns true.
+// In that case x represents the uninstantiated function value and
+// it is the caller's responsibility to instantiate the function.
+func (check *Checker) indexExpr(x *operand, e *ast.IndexExpr) (isFuncInst bool) {
 	check.exprOrType(x, e.X)
-	if x.mode == invalid {
-		check.use(typeparams.UnpackExpr(e.Index)...)
-		return
-	}
 
-	if x.mode == typexpr {
+	switch x.mode {
+	case invalid:
+		check.use(typeparams.UnpackExpr(e.Index)...)
+		return false
+
+	case typexpr:
 		// type instantiation
 		x.mode = invalid
 		x.typ = check.varType(e)
 		if x.typ != Typ[Invalid] {
 			x.mode = typexpr
 		}
-		return
-	}
+		return false
 
-	if x.mode == value {
+	case value:
 		if sig := asSignature(x.typ); sig != nil && len(sig.tparams) > 0 {
-			check.funcInst(x, e)
-			return
+			// function instantiation
+			return true
 		}
 	}
 
@@ -181,6 +184,7 @@ func (check *Checker) indexExpr(x *operand, e *ast.IndexExpr) {
 	}
 
 	check.index(e.Index, length)
+	return false
 }
 
 func (check *Checker) sliceExpr(x *operand, e *ast.SliceExpr) {