[dev.typeparams] cmd/compile/internal/types2: use syntax printer to print expressions

The syntax package has a full-fledged node printer. Use that printer
to create the expression strings needed in error messages, and remove
the local (essentially) duplicate code for creating expression strings.

Change-Id: I03673e5e79b3c1470f8073ebbe840a90fd9053ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/282553
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

8 files changed, 15 insertions, 307 deletions

diff --git a/src/cmd/compile/internal/types2/api.go b/src/cmd/compile/internal/types2/api.go
index c5c30babff..3348ccb900 100644
--- a/src/cmd/compile/internal/types2/api.go
+++ b/src/cmd/compile/internal/types2/api.go
@@ -379,7 +379,7 @@ func (init *Initializer) String() string {
 		buf.WriteString(lhs.Name())
 	}
 	buf.WriteString(" = ")
-	WriteExpr(&buf, init.Rhs)
+	syntax.Fprint(&buf, init.Rhs, syntax.ShortForm)
 	return buf.String()
 }
 
diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index 58d7df2f1d..c1327b179c 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -151,7 +151,7 @@ func TestValuesInfo(t *testing.T) {
 		// look for expression
 		var expr syntax.Expr
 		for e := range info.Types {
-			if ExprString(e) == test.expr {
+			if syntax.ShortString(e) == test.expr {
 				expr = e
 				break
 			}
@@ -306,7 +306,7 @@ func TestTypesInfo(t *testing.T) {
 		// look for expression type
 		var typ Type
 		for e, tv := range info.Types {
-			if ExprString(e) == test.expr {
+			if syntax.ShortString(e) == test.expr {
 				typ = tv.Type
 				break
 			}
@@ -454,7 +454,7 @@ func TestInferredInfo(t *testing.T) {
 			default:
 				panic(fmt.Sprintf("unexpected call expression type %T", call))
 			}
-			if ExprString(fun) == test.fun {
+			if syntax.ShortString(fun) == test.fun {
 				targs = inf.Targs
 				sig = inf.Sig
 				break
@@ -733,8 +733,8 @@ func TestPredicatesInfo(t *testing.T) {
 		// look for expression predicates
 		got := "<missing>"
 		for e, tv := range info.Types {
-			//println(name, ExprString(e))
-			if ExprString(e) == test.expr {
+			//println(name, syntax.ShortString(e))
+			if syntax.ShortString(e) == test.expr {
 				got = predString(tv)
 				break
 			}
diff --git a/src/cmd/compile/internal/types2/assignments.go b/src/cmd/compile/internal/types2/assignments.go
index b367aa76da..0fa9c6b8e6 100644
--- a/src/cmd/compile/internal/types2/assignments.go
+++ b/src/cmd/compile/internal/types2/assignments.go
@@ -197,7 +197,7 @@ func (check *Checker) assignVar(lhs syntax.Expr, x *operand) Type {
 			var op operand
 			check.expr(&op, sel.X)
 			if op.mode == mapindex {
-				check.errorf(&z, "cannot assign to struct field %s in map", ExprString(z.expr))
+				check.errorf(&z, "cannot assign to struct field %s in map", syntax.ShortString(z.expr))
 				return nil
 			}
 		}
diff --git a/src/cmd/compile/internal/types2/builtins_test.go b/src/cmd/compile/internal/types2/builtins_test.go
index 9f737bc9bb..0fc7c17d3e 100644
--- a/src/cmd/compile/internal/types2/builtins_test.go
+++ b/src/cmd/compile/internal/types2/builtins_test.go
@@ -176,7 +176,7 @@ func testBuiltinSignature(t *testing.T, name, src0, want string) {
 		// the recorded type for the built-in must match the wanted signature
 		typ := types[fun].Type
 		if typ == nil {
-			t.Errorf("%s: no type recorded for %s", src0, ExprString(fun))
+			t.Errorf("%s: no type recorded for %s", src0, syntax.ShortString(fun))
 			return
 		}
 		if got := typ.String(); got != want {
diff --git a/src/cmd/compile/internal/types2/errors.go b/src/cmd/compile/internal/types2/errors.go
index 941e7c6fd3..d74980253e 100644
--- a/src/cmd/compile/internal/types2/errors.go
+++ b/src/cmd/compile/internal/types2/errors.go
@@ -53,7 +53,7 @@ func (check *Checker) sprintf(format string, args ...interface{}) string {
 		case syntax.Pos:
 			arg = a.String()
 		case syntax.Expr:
-			arg = ExprString(a)
+			arg = syntax.ShortString(a)
 		case Object:
 			arg = ObjectString(a, check.qualifier)
 		case Type:
diff --git a/src/cmd/compile/internal/types2/exprstring.go b/src/cmd/compile/internal/types2/exprstring.go
deleted file mode 100644
index 0ec5d1338f..0000000000
--- a/src/cmd/compile/internal/types2/exprstring.go
+++ /dev/null
@@ -1,293 +0,0 @@
-// UNREVIEWED
-// Copyright 2013 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.
-
-// This file implements printing of expressions.
-
-package types2
-
-import (
-	"bytes"
-	"cmd/compile/internal/syntax"
-)
-
-// ExprString returns the (possibly shortened) string representation for x.
-// Shortened representations are suitable for user interfaces but may not
-// necessarily follow Go syntax.
-func ExprString(x syntax.Expr) string {
-	var buf bytes.Buffer
-	WriteExpr(&buf, x)
-	return buf.String()
-}
-
-// WriteExpr writes the (possibly shortened) string representation for x to buf.
-// Shortened representations are suitable for user interfaces but may not
-// necessarily follow Go syntax.
-func WriteExpr(buf *bytes.Buffer, x syntax.Expr) {
-	// The AST preserves source-level parentheses so there is
-	// no need to introduce them here to correct for different
-	// operator precedences. (This assumes that the AST was
-	// generated by a Go parser.)
-
-	// TODO(gri): This assumption is not correct - we need to recreate
-	//            parentheses in expressions.
-
-	switch x := x.(type) {
-	default:
-		buf.WriteString("(ast: bad expr)") // nil, syntax.BadExpr, syntax.KeyValueExpr
-
-	case *syntax.Name:
-		buf.WriteString(x.Value)
-
-	case *syntax.DotsType:
-		buf.WriteString("...")
-		if x.Elem != nil {
-			WriteExpr(buf, x.Elem)
-		}
-
-	case *syntax.BasicLit:
-		buf.WriteString(x.Value)
-
-	case *syntax.FuncLit:
-		WriteExpr(buf, x.Type)
-		if x.Body != nil && len(x.Body.List) > 0 {
-			buf.WriteString(" {…}") // shortened
-		} else {
-			buf.WriteString(" {}")
-		}
-
-	case *syntax.CompositeLit:
-		WriteExpr(buf, x.Type)
-		if len(x.ElemList) > 0 {
-			buf.WriteString("{…}") // shortened
-		} else {
-			buf.WriteString("{}")
-		}
-
-	case *syntax.ParenExpr:
-		buf.WriteByte('(')
-		WriteExpr(buf, x.X)
-		buf.WriteByte(')')
-
-	case *syntax.SelectorExpr:
-		WriteExpr(buf, x.X)
-		buf.WriteByte('.')
-		buf.WriteString(x.Sel.Value)
-
-	case *syntax.IndexExpr:
-		WriteExpr(buf, x.X)
-		buf.WriteByte('[')
-		WriteExpr(buf, x.Index) // x.Index may be a *ListExpr
-		buf.WriteByte(']')
-
-	case *syntax.SliceExpr:
-		WriteExpr(buf, x.X)
-		buf.WriteByte('[')
-		if x.Index[0] != nil {
-			WriteExpr(buf, x.Index[0])
-		}
-		buf.WriteByte(':')
-		if x.Index[1] != nil {
-			WriteExpr(buf, x.Index[1])
-		}
-		if x.Full {
-			buf.WriteByte(':')
-			if x.Index[2] != nil {
-				WriteExpr(buf, x.Index[2])
-			}
-		}
-		buf.WriteByte(']')
-
-	case *syntax.AssertExpr:
-		WriteExpr(buf, x.X)
-		buf.WriteString(".(")
-		WriteExpr(buf, x.Type)
-		buf.WriteByte(')')
-
-	case *syntax.CallExpr:
-		WriteExpr(buf, x.Fun)
-		buf.WriteByte('(')
-		writeExprList(buf, x.ArgList)
-		if x.HasDots {
-			buf.WriteString("...")
-		}
-		buf.WriteByte(')')
-
-	case *syntax.ListExpr:
-		writeExprList(buf, x.ElemList)
-
-	case *syntax.Operation:
-		// TODO(gri) This would be simpler if x.X == nil meant unary expression.
-		if x.Y == nil {
-			// unary expression
-			buf.WriteString(x.Op.String())
-			WriteExpr(buf, x.X)
-		} else {
-			// binary expression
-			WriteExpr(buf, x.X)
-			buf.WriteByte(' ')
-			buf.WriteString(x.Op.String())
-			buf.WriteByte(' ')
-			WriteExpr(buf, x.Y)
-		}
-
-		// case *ast.StarExpr:
-		// 	buf.WriteByte('*')
-		// 	WriteExpr(buf, x.X)
-
-		// case *ast.UnaryExpr:
-		// 	buf.WriteString(x.Op.String())
-		// 	WriteExpr(buf, x.X)
-
-		// case *ast.BinaryExpr:
-		// 	WriteExpr(buf, x.X)
-		// 	buf.WriteByte(' ')
-		// 	buf.WriteString(x.Op.String())
-		// 	buf.WriteByte(' ')
-		// 	WriteExpr(buf, x.Y)
-
-	case *syntax.ArrayType:
-		if x.Len == nil {
-			buf.WriteString("[...]")
-		} else {
-			buf.WriteByte('[')
-			WriteExpr(buf, x.Len)
-			buf.WriteByte(']')
-		}
-		WriteExpr(buf, x.Elem)
-
-	case *syntax.SliceType:
-		buf.WriteString("[]")
-		WriteExpr(buf, x.Elem)
-
-	case *syntax.StructType:
-		buf.WriteString("struct{")
-		writeFieldList(buf, x.FieldList, "; ", false)
-		buf.WriteByte('}')
-
-	case *syntax.FuncType:
-		buf.WriteString("func")
-		writeSigExpr(buf, x)
-
-	case *syntax.InterfaceType:
-		// separate type list types from method list
-		// TODO(gri) we can get rid of this extra code if writeExprList does the separation
-		var types []syntax.Expr
-		var methods []*syntax.Field
-		for _, f := range x.MethodList {
-			if f.Name != nil && f.Name.Value == "type" {
-				// type list type
-				types = append(types, f.Type)
-			} else {
-				// method or embedded interface
-				methods = append(methods, f)
-			}
-		}
-
-		buf.WriteString("interface{")
-		writeFieldList(buf, methods, "; ", true)
-		if len(types) > 0 {
-			if len(methods) > 0 {
-				buf.WriteString("; ")
-			}
-			buf.WriteString("type ")
-			writeExprList(buf, types)
-		}
-		buf.WriteByte('}')
-
-	case *syntax.MapType:
-		buf.WriteString("map[")
-		WriteExpr(buf, x.Key)
-		buf.WriteByte(']')
-		WriteExpr(buf, x.Value)
-
-	case *syntax.ChanType:
-		var s string
-		switch x.Dir {
-		case syntax.SendOnly:
-			s = "chan<- "
-		case syntax.RecvOnly:
-			s = "<-chan "
-		default:
-			s = "chan "
-		}
-		buf.WriteString(s)
-		if e, _ := x.Elem.(*syntax.ChanType); x.Dir != syntax.SendOnly && e != nil && e.Dir == syntax.RecvOnly {
-			// don't print chan (<-chan T) as chan <-chan T (but chan<- <-chan T is ok)
-			buf.WriteByte('(')
-			WriteExpr(buf, x.Elem)
-			buf.WriteByte(')')
-		} else {
-			WriteExpr(buf, x.Elem)
-		}
-	}
-}
-
-func writeSigExpr(buf *bytes.Buffer, sig *syntax.FuncType) {
-	buf.WriteByte('(')
-	writeFieldList(buf, sig.ParamList, ", ", false)
-	buf.WriteByte(')')
-
-	res := sig.ResultList
-	n := len(res)
-	if n == 0 {
-		// no result
-		return
-	}
-
-	buf.WriteByte(' ')
-	if n == 1 && res[0].Name == nil {
-		// single unnamed result
-		WriteExpr(buf, res[0].Type)
-		return
-	}
-
-	// multiple or named result(s)
-	buf.WriteByte('(')
-	writeFieldList(buf, res, ", ", false)
-	buf.WriteByte(')')
-}
-
-func writeFieldList(buf *bytes.Buffer, list []*syntax.Field, sep string, iface bool) {
-	for i := 0; i < len(list); {
-		f := list[i]
-		if i > 0 {
-			buf.WriteString(sep)
-		}
-
-		// if we don't have a name, we have an embedded type
-		if f.Name == nil {
-			WriteExpr(buf, f.Type)
-			i++
-			continue
-		}
-
-		// types of interface methods consist of signatures only
-		if sig, _ := f.Type.(*syntax.FuncType); sig != nil && iface {
-			buf.WriteString(f.Name.Value)
-			writeSigExpr(buf, sig)
-			i++
-			continue
-		}
-
-		// write the type only once for a sequence of fields with the same type
-		t := f.Type
-		buf.WriteString(f.Name.Value)
-		for i++; i < len(list) && list[i].Type == t; i++ {
-			buf.WriteString(", ")
-			buf.WriteString(list[i].Name.Value)
-		}
-		buf.WriteByte(' ')
-		WriteExpr(buf, t)
-	}
-}
-
-func writeExprList(buf *bytes.Buffer, list []syntax.Expr) {
-	for i, x := range list {
-		if i > 0 {
-			buf.WriteString(", ")
-		}
-		WriteExpr(buf, x)
-	}
-}
diff --git a/src/cmd/compile/internal/types2/exprstring_test.go b/src/cmd/compile/internal/types2/exprstring_test.go
index efb7c308b7..39e1354eac 100644
--- a/src/cmd/compile/internal/types2/exprstring_test.go
+++ b/src/cmd/compile/internal/types2/exprstring_test.go
@@ -9,9 +9,9 @@ import (
 	"testing"
 
 	"cmd/compile/internal/syntax"
-	. "cmd/compile/internal/types2"
 )
 
+// TODO(gri) move these tests into syntax package
 var testExprs = []testEntry{
 	// basic type literals
 	dup("x"),
@@ -24,8 +24,9 @@ var testExprs = []testEntry{
 	dup("`bar`"),
 
 	// func and composite literals
-	{"func(){}", "func() {}"},
-	{"func(x int) complex128 {}", "func(x int) complex128 {}"},
+	dup("func() {}"),
+	dup("[]int{}"),
+	{"func(x int) complex128 { return 0 }", "func(x int) complex128 {…}"},
 	{"[]int{1, 2, 3}", "[]int{…}"},
 
 	// non-type expressions
@@ -90,7 +91,7 @@ func TestExprString(t *testing.T) {
 			continue
 		}
 		x := f.DeclList[0].(*syntax.VarDecl).Values
-		if got := ExprString(x); got != test.str {
+		if got := syntax.ShortString(x); got != test.str {
 			t.Errorf("%s: got %s, want %s", test.src, got, test.str)
 		}
 	}
diff --git a/src/cmd/compile/internal/types2/operand.go b/src/cmd/compile/internal/types2/operand.go
index 0a19760423..ab4a7eb4f3 100644
--- a/src/cmd/compile/internal/types2/operand.go
+++ b/src/cmd/compile/internal/types2/operand.go
@@ -110,7 +110,7 @@ func operandString(x *operand, qf Qualifier) string {
 
 	var expr string
 	if x.expr != nil {
-		expr = ExprString(x.expr)
+		expr = syntax.ShortString(x.expr)
 	} else {
 		switch x.mode {
 		case builtin: