gofmt, go/printer: update internal estimated position correctly

Fixes #1089.

R=rsc
CC=golang-dev
https://golang.org/cl/2172043

src/pkg/go/printer/printer.go

@@ -209,6 +209,11 @@ func (p *printer) write(data []byte) {
 
 		case tabwriter.Escape:
 			p.escape = !p.escape
+
+			// ignore escape chars introduced by printer - they are
+			// invisible and must not affect p.pos (was issue #1089)
+			p.pos.Offset--
+			p.pos.Column--
 		}
 	}
 

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

@@ -431,6 +431,38 @@ func _() {
 }
 
 
+// Comments immediately adjacent to punctuation (for which the go/printer
+// may obly have estimated position information) must remain after the punctuation.
+func _() {
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		/* comment before literal */ 1,
+		2,	/* comment before comma - ok to move after comma */
+		3,	/* comment before comma - ok to move after comma */
+	}
+
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment after semicolon */
+	i++ {		// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment before semicolon - ok to move after semicolon */
+	i++ /* comment before opening curly brace */ {
+	}
+}
+
+
 // Line comments with tabs
 func _() {
 	var finput *bufio.Reader	// input file

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

@@ -429,6 +429,40 @@ func _() {
 	/* closing curly brace should be on new line */ }
 
 
+// Comments immediately adjacent to punctuation (for which the go/printer
+// may obly have estimated position information) must remain after the punctuation.
+func _() {
+	_ = T{
+		1,    // comment after comma
+		2,    /* comment after comma */
+		3  ,  // comment after comma
+	}
+	_ = T{
+		1  ,// comment after comma
+		2  ,/* comment after comma */
+		3,// comment after comma
+	}
+	_ = T{
+		/* comment before literal */1,
+		2/* comment before comma - ok to move after comma */,
+		3  /* comment before comma - ok to move after comma */  ,
+	}
+
+	for
+		i=0;// comment after semicolon
+		i<9;/* comment after semicolon */
+		i++{// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for
+		i=0;// comment after semicolon
+		i<9/* comment before semicolon - ok to move after semicolon */;
+		i++ /* comment before opening curly brace */ {
+	}
+}
+
+
 // Line comments with tabs
 func _() {
 var	finput		*bufio.Reader			// input file

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

@@ -335,7 +335,6 @@ func _() {
 		2,
 		3,
 	)
-	// TODO(gri) the cases below are not correct yet
 	f(1,
 		2,
 		3)	// comment
@@ -348,8 +347,7 @@ func _() {
 		3)	// comment
 	f(1,
 		2,
-		3 // comment
-		,
+		3,	// comment
 	)
 }
 

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

@@ -328,7 +328,6 @@ func _() {
 		2,
 		3,
 	)
-	// TODO(gri) the cases below are not correct yet
 	f(1,
 		2,
 		3)  // comment

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

@@ -335,7 +335,6 @@ func _() {
 		2,
 		3,
 	)
-	// TODO(gri) the cases below are not correct yet
 	f(1,
 		2,
 		3)	// comment
@@ -348,8 +347,7 @@ func _() {
 		3)	// comment
 	f(1,
 		2,
-		3 // comment
-		,
+		3,	// comment
 	)
 }