go/printer, gofmt: handle raw string literals containing newlines better

A raw string containing newlines breaks whatever columns structure
has been established so far. Recognize the situation and force a
new section of alignment with the first line break seen after the
the raw string.

Applied gofmt to src and misc.

Fixes #9064.

Change-Id: I961e94b529b1fd421908311f366b113e2ec9b7f0
Reviewed-on: https://go-review.googlesource.com/105040
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/ssa/gen/386Ops.go

@@ -135,7 +135,7 @@ func init() {
 
 		fp01     = regInfo{inputs: nil, outputs: fponly}
 		fp21     = regInfo{inputs: []regMask{fp, fp}, outputs: fponly}
-		fp21load  = regInfo{inputs: []regMask{fp, gpspsb, 0}, outputs: fponly}
+		fp21load = regInfo{inputs: []regMask{fp, gpspsb, 0}, outputs: fponly}
 		fpgp     = regInfo{inputs: fponly, outputs: gponly}
 		gpfp     = regInfo{inputs: gponly, outputs: fponly}
 		fp11     = regInfo{inputs: fponly, outputs: fponly}
@@ -531,4 +531,4 @@ func init() {
 		framepointerreg: int8(num["BP"]),
 		linkreg:         -1, // not used
 	})
-}
+}

src/go/printer/printer.go

@@ -55,14 +55,15 @@ type printer struct {
 	fset *token.FileSet
 
 	// Current state
-	output      []byte       // raw printer result
-	indent      int          // current indentation
-	level       int          // level == 0: outside composite literal; level > 0: inside composite literal
-	mode        pmode        // current printer mode
-	impliedSemi bool         // if set, a linebreak implies a semicolon
-	lastTok     token.Token  // last token printed (token.ILLEGAL if it's whitespace)
-	prevOpen    token.Token  // previous non-brace "open" token (, [, or token.ILLEGAL
-	wsbuf       []whiteSpace // delayed white space
+	output       []byte       // raw printer result
+	indent       int          // current indentation
+	level        int          // level == 0: outside composite literal; level > 0: inside composite literal
+	mode         pmode        // current printer mode
+	endAlignment bool         // if set, terminate alignment immediately
+	impliedSemi  bool         // if set, a linebreak implies a semicolon
+	lastTok      token.Token  // last token printed (token.ILLEGAL if it's whitespace)
+	prevOpen     token.Token  // previous non-brace "open" token (, [, or token.ILLEGAL
+	wsbuf        []whiteSpace // delayed white space
 
 	// Positions
 	// The out position differs from the pos position when the result
@@ -232,6 +233,20 @@ func (p *printer) writeIndent() {
 // writeByte writes ch n times to p.output and updates p.pos.
 // Only used to write formatting (white space) characters.
 func (p *printer) writeByte(ch byte, n int) {
+	if p.endAlignment {
+		// Ignore any alignment control character;
+		// and at the end of the line, break with
+		// a formfeed to indicate termination of
+		// existing columns.
+		switch ch {
+		case '\t', '\v':
+			ch = ' '
+		case '\n', '\f':
+			ch = '\f'
+			p.endAlignment = false
+		}
+	}
+
 	if p.out.Column == 1 {
 		// no need to write line directives before white space
 		p.writeIndent()
@@ -298,10 +313,15 @@ func (p *printer) writeString(pos token.Position, s string, isLit bool) {
 	nlines := 0
 	var li int // index of last newline; valid if nlines > 0
 	for i := 0; i < len(s); i++ {
-		// Go tokens cannot contain '\f' - no need to look for it
-		if s[i] == '\n' {
+		// Raw string literals may contain any character except back quote (`).
+		if ch := s[i]; ch == '\n' || ch == '\f' {
+			// account for line break
 			nlines++
 			li = i
+			// A line break inside a literal will break whatever column
+			// formatting is in place; ignore any further alignment through
+			// the end of the line.
+			p.endAlignment = true
 		}
 	}
 	p.pos.Offset += len(s)

src/go/printer/testdata/linebreaks.golden

@@ -256,7 +256,7 @@ func _(
 ) {
 }
 
-// Example from issue 2597.
+// Example from issue #2597.
 func ManageStatus0(
 	in <-chan *Status,
 	req <-chan Request,
@@ -272,4 +272,24 @@ func ManageStatus1(
 ) {
 }
 
+// Example from issue #9064.
+func (y *y) xerrors() error {
+	_ = "xerror.test"	//TODO-
+	_ = []byte(`
+foo bar foo bar foo bar
+`) //TODO-
+}
+
+func _() {
+	_ = "abc"		// foo
+	_ = `abc_0123456789_`	// foo
+}
+
+func _() {
+	_ = "abc"	// foo
+	_ = `abc
+0123456789
+` // foo
+}
+
 // There should be exactly one linebreak after this comment.

src/go/printer/testdata/linebreaks.input

@@ -252,7 +252,7 @@ func _(
        y T,
 ) {}
 
-// Example from issue 2597.
+// Example from issue #2597.
 func ManageStatus0(
 	in <-chan *Status,
 	req <-chan Request,
@@ -267,5 +267,25 @@ func ManageStatus1(
 	TargetHistorySize int,
 ) {
 }
-    
+
+// Example from issue #9064.
+func (y *y) xerrors() error {
+	_ = "xerror.test" //TODO-
+	_ = []byte(`
+foo bar foo bar foo bar
+`) //TODO-
+}
+
+func _() {
+	_ = "abc" // foo
+	_ = `abc_0123456789_` // foo
+}
+
+func _() {
+	_ = "abc" // foo
+	_ = `abc
+0123456789
+` // foo
+}
+
 // There should be exactly one linebreak after this comment.