gofmt: preserve syntactically relevant blanks between ints and tokens that start with a '.' (2nd attempt)

R=rsc
CC=golang-dev
https://golang.org/cl/2270042

src/pkg/go/printer/nodes.go

@@ -848,14 +848,6 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int, ctxt exprContext, multi
 		p.print(x.Lparen, token.LPAREN)
 		p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
 		if x.Ellipsis.IsValid() {
-			if p.lastTok == token.INT {
-				// w/o a blank, the previous int will become a float
-				// (this could be solved more generally in the print
-				// function but it appears that this is the only
-				// place in the grammar where a token starting with
-				// a do may legally extend the previous token)
-				p.print(blank)
-			}
 			p.print(x.Ellipsis, token.ELLIPSIS)
 		}
 		p.print(x.Rparen, token.RPAREN)

src/pkg/go/printer/printer.go

@@ -802,10 +802,19 @@ func (p *printer) print(args ...interface{}) {
 			data = []byte("\xff" + string(data) + "\xff")
 			tok = x.Kind
 		case token.Token:
+			s := x.String()
+			if p.lastTok == token.INT && s[0] == '.' {
+				// separate int with blank from '.' so it doesn't become a float
+				if len(p.buffer) != 0 {
+					p.internalError("whitespace buffer not empty")
+				}
+				p.buffer = p.buffer[0:1]
+				p.buffer[0] = ' '
+			}
 			if p.Styler != nil {
 				data, tag = p.Styler.Token(x)
 			} else {
-				data = []byte(x.String())
+				data = []byte(s)
 			}
 			tok = x
 		case token.Position:

src/pkg/go/printer/testdata/expressions.golden

@@ -184,6 +184,16 @@ func f(x int, args ...int) {
 	f(9, .42...)
 	f(10, 42e0...)
 	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
 }
 
 

src/pkg/go/printer/testdata/expressions.input

@@ -184,6 +184,16 @@ func f(x int, args ...int) {
 	f(9, .42...)
 	f(10, 42e0 ...)
 	f(11, 42e0...)
+
+	_ = 42 .x // a blank must remain between 42 and .x
+	_ = 42. .x
+	_ = 42..x
+	_ = 42.0 .x
+	_ = 42.0.x
+	_ = .42 .x
+	_ = .42.x
+	_ = 42e0 .x
+	_ = 42e0.x
 }
 
 

src/pkg/go/printer/testdata/expressions.raw

@@ -184,6 +184,16 @@ func f(x int, args ...int) {
 	f(9, .42...)
 	f(10, 42e0...)
 	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
 }