- blank before opening { for multi-line composite literals (as preferred by r)

- blank padding around composite literal contents for a less dense look
  (most if not all composite literals were written in that style before gofmt
  ran through them)
- corresponding (internal) flag: compositeLitBlank

- don't print a semi after a one-statement statement list (as preferred by r)
- corresponding (internal flag): fewerSemis

- the number of changes in nodes.go is huge because of the removed semis;
  hg mail requires that I gofmt the file before

With both flags set to false, this CL causes no gofmt formatting change. We
can turn them on if we like it (and then remove the flags). Will submit with
flags disabled.

R=rsc, r
http://go/go-review/1025015

src/pkg/go/printer/nodes.go

@@ -19,6 +19,7 @@ import (
 // Disabled formatting - enable eventually and remove the flag.
 const (
 	compositeLitBlank	= false;
+	fewerSemis		= false;
 	stringListMode		= exprListMode(0);	// previously: noIndent
 )
 
@@ -133,7 +134,8 @@ func (p *printer) stringList(list []*ast.BasicLit, multiLine *bool) {
 type exprListMode uint
 
 const (
-	blankStart	exprListMode	= 1<<iota;	// print a blank before the list
+	blankStart	exprListMode	= 1<<iota;	// print a blank before a non-empty list
+	blankEnd;			// print a blank after a non-empty list
 	commaSep;			// elements are separated by commas
 	commaTerm;			// elements are terminated by comma
 	noIndent;			// no extra indentation in multi-line lists
@@ -170,6 +172,9 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, mode exprListMo
 			}
 			p.expr(x, multiLine);
 		}
+		if mode&blankEnd != 0 {
+			p.print(blank);
+		}
 		return;
 	}
 
@@ -206,15 +211,23 @@ func (p *printer) exprList(prev token.Position, list []ast.Expr, mode exprListMo
 		}
 		p.expr(x, multiLine);
 	}
+
 	if mode & commaTerm != 0 {
 		p.print(token.COMMA);
 		if ws == ignore && mode&noIndent == 0 {
-			// should always be indented here since we have a multi-line
-			// expression list - be conservative and check anyway
+			// unindent if we indented
 			p.print(unindent);
 		}
 		p.print(formfeed);	// terminating comma needs a line break to look good
-	} else if ws == ignore && mode&noIndent == 0 {
+		return;
+	}
+
+	if mode&blankEnd != 0 {
+		p.print(blank);
+	}
+
+	if ws == ignore && mode&noIndent == 0 {
+		// unindent if we indented
 		p.print(unindent);
 	}
 }
@@ -264,7 +277,9 @@ func (p *printer) signature(params, result []*ast.Field, multiLine *bool) (optSe
 func identListSize(list []*ast.Ident, maxSize int) (size int) {
 	for i, x := range list {
 		if i > 0 {
-			size += 2;	// ", "
+			size += 2 // ", "
+			;
+
 		}
 		size += len(x.Value);
 		if size >= maxSize {
@@ -287,7 +302,9 @@ func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
 	const maxSize = 30;	// adjust as appropriate, this is an approximate value
 	namesSize := identListSize(f.Names, maxSize);
 	if namesSize > 0 {
-		namesSize = 1;	// blank between names and types
+		namesSize = 1 // blank between names and types
+		;
+
 	}
 	typeSize := p.nodeSize(f.Type, maxSize);
 	return namesSize + typeSize <= maxSize;
@@ -609,15 +626,21 @@ func (p *printer) expr1(expr ast.Expr, prec1 int, ctxt Context, multiLine *bool)
 
 	case *ast.CompositeLit:
 		p.expr1(x.Type, token.HighestPrec, compositeLit, multiLine);
-		if compositeLitBlank && x.Lbrace.Line < x.Rbrace.Line {
-			// add a blank before the opening { for multi-line composites
-			// TODO(gri): for now this decision is made by looking at the
-			//            source code - it may not be correct if the source
-			//            code was badly misformatted in the first place
-			p.print(blank);
+		mode := commaSep | commaTerm;
+		if compositeLitBlank {
+			// add blank padding around composite literal
+			// contents for a less dense look
+			mode |= blankStart | blankEnd;
+			if x.Lbrace.Line < x.Rbrace.Line {
+				// add a blank before the opening { for multi-line composites
+				// TODO(gri): for now this decision is made by looking at the
+				//            source code - it may not be correct if the source
+				//            code was badly misformatted in the first place
+				p.print(blank);
+			}
 		}
 		p.print(x.Lbrace, token.LBRACE);
-		p.exprList(x.Lbrace, x.Elts, commaSep | commaTerm, multiLine);
+		p.exprList(x.Lbrace, x.Elts, mode, multiLine);
 		p.print(x.Rbrace, token.RBRACE);
 
 	case *ast.Ellipsis:
@@ -697,7 +720,7 @@ func (p *printer) stmtList(list []ast.Stmt, _indent int) {
 		// in those cases each clause is a new section
 		p.linebreak(s.Pos().Line, 1, maxStmtNewlines, ignore, i == 0 || _indent == 0 || multiLine);
 		multiLine = false;
-		if !p.stmt(s, &multiLine) {
+		if !p.stmt(s, &multiLine) && (!fewerSemis || len(list) > 1) {
 			p.print(token.SEMICOLON);
 		}
 	}