syntax: avoid extra newlines when printing case clauses

If we remove any newlines when printing, don't insert others later on in
the source.

While here, improve how we keep track of p.line throughout the printer.

Fixes #779.

CHANGELOG.md

@@ -12,6 +12,7 @@ This release drops support for Go 1.17 and includes many features and fixes.
   - Don't require peeking two bytes after `echo *` - [#835]
   - Simplify `${name:-}` to the equivalent `${name-}` - [#849]
   - Don't print trailing whitespaces on nested subshells - [#814]
+  - Don't print extra newlines in some case clauses - [#779]
   - Allow escaped newlines before unquoted words again - [#873]
   - Parse a redirections edge case without spaces - [#879]
   - Give a helpful error when `<<<` is used in POSIX mode - [#881]
@@ -654,6 +655,7 @@ module in v3.
 
 Initial release.
 
+[#779]: https://github.com/mvdan/sh/issues/779
 [#803]: https://github.com/mvdan/sh/issues/803
 [#814]: https://github.com/mvdan/sh/issues/814
 [#835]: https://github.com/mvdan/sh/issues/835

syntax/printer.go

@@ -359,7 +359,7 @@ func (p *Printer) semiOrNewl(s string, pos Pos) {
 		if !p.minify {
 			p.space()
 		}
-		p.line = pos.Line()
+		p.advanceLine(pos.Line())
 	}
 	p.WriteString(s)
 	p.wantSpace = spaceRequired
@@ -415,14 +415,19 @@ func (p *Printer) indent() {
 
 // TODO(mvdan): add an indent call at the end of newline?
 
+// newline prints one newline and advances p.line to pos.Line().
 func (p *Printer) newline(pos Pos) {
 	p.flushHeredocs()
 	p.flushComments()
 	p.WriteByte('\n')
 	p.wantSpace = spaceWritten
 	p.wantNewline, p.mustNewline = false, false
-	if p.line < pos.Line() {
-		p.line++
+	p.advanceLine(pos.Line())
+}
+
+func (p *Printer) advanceLine(line uint) {
+	if p.line < line {
+		p.line = line
 	}
 }
 
@@ -486,7 +491,7 @@ func (p *Printer) flushHeredocs() {
 		if r.Hdoc != nil {
 			// Overwrite p.line, since printing r.Word again can set
 			// p.line to the beginning of the heredoc again.
-			p.line = r.Hdoc.End().Line()
+			p.advanceLine(r.Hdoc.End().Line())
 		}
 		p.wantSpace = spaceNotRequired
 	}
@@ -495,6 +500,8 @@ func (p *Printer) flushHeredocs() {
 	p.mustNewline = true
 }
 
+// newline prints between zero and two newlines.
+// If any newlines are printed, it advances p.line to pos.Line().
 func (p *Printer) newlines(pos Pos) {
 	if p.firstLine && len(p.pendingComments) == 0 {
 		p.firstLine = false
@@ -503,14 +510,17 @@ func (p *Printer) newlines(pos Pos) {
 	if !p.wantsNewline(pos) {
 		return
 	}
-	p.newline(pos)
-	if pos.Line() > p.line {
-		if !p.minify {
-			// preserve single empty lines
-			p.WriteByte('\n')
-		}
-		p.line++
+	p.flushHeredocs()
+	p.flushComments()
+	p.WriteByte('\n')
+	p.wantSpace = spaceWritten
+	p.wantNewline, p.mustNewline = false, false
+
+	l := pos.Line()
+	if l > p.line+1 && !p.minify {
+		p.WriteByte('\n') // preserve single empty lines
 	}
+	p.advanceLine(l)
 	p.indent()
 }
 
@@ -567,9 +577,7 @@ func (p *Printer) flushComments() {
 			p.space()
 		}
 		// don't go back one line, which may happen in some edge cases
-		if p.line < cline {
-			p.line = cline
-		}
+		p.advanceLine(cline)
 		p.WriteByte('#')
 		p.writeLit(strings.TrimRightFunc(c.Text, unicode.IsSpace))
 		p.wantNewline = true
@@ -617,7 +625,7 @@ func (p *Printer) wordParts(wps []WordPart, quoted bool) {
 			p.line++
 		}
 		p.wordPart(wp, next)
-		p.line = wp.End().Line()
+		p.advanceLine(wp.End().Line())
 	}
 }
 
@@ -632,11 +640,11 @@ func (p *Printer) wordPart(wp, next WordPart) {
 		p.WriteByte('\'')
 		p.writeLit(x.Value)
 		p.WriteByte('\'')
-		p.line = x.End().Line()
+		p.advanceLine(x.End().Line())
 	case *DblQuoted:
 		p.dblQuoted(x)
 	case *CmdSubst:
-		p.line = x.Pos().Line()
+		p.advanceLine(x.Pos().Line())
 		switch {
 		case x.TempFile:
 			p.WriteString("${")
@@ -863,7 +871,7 @@ func (p *Printer) testExpr(expr TestExpr) {
 }
 
 func (p *Printer) testExprSameLine(expr TestExpr) {
-	p.line = expr.Pos().Line()
+	p.advanceLine(expr.Pos().Line())
 	switch x := expr.(type) {
 	case *Word:
 		p.word(x)
@@ -1046,7 +1054,7 @@ func (p *Printer) stmt(s *Stmt) {
 }
 
 func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
-	p.line = cmd.Pos().Line()
+	p.advanceLine(cmd.Pos().Line())
 	p.spacePad(cmd.Pos())
 	switch x := cmd.(type) {
 	case *CallExpr:
@@ -1133,7 +1141,7 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 		if p.minify || p.singleLine || x.Y.Pos().Line() <= p.line {
 			// leave p.nestedBinary untouched
 			p.spacedToken(x.Op.String(), x.OpPos)
-			p.line = x.Y.Pos().Line()
+			p.advanceLine(x.Y.Pos().Line())
 			p.stmt(x.Y)
 			break
 		}
@@ -1156,12 +1164,12 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 			}
 		} else {
 			p.spacedToken(x.Op.String(), x.OpPos)
-			p.line = x.OpPos.Line()
+			p.advanceLine(x.OpPos.Line())
 			p.comments(x.Y.Comments...)
 			p.newline(Pos{})
 			p.indent()
 		}
-		p.line = x.Y.Pos().Line()
+		p.advanceLine(x.Y.Pos().Line())
 		_, p.nestedBinary = x.Y.Cmd.(*BinaryCmd)
 		p.stmt(x.Y)
 		if indent {
@@ -1182,13 +1190,14 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 		} else if !x.Parens || !p.minify {
 			p.space()
 		}
-		p.line = x.Body.Pos().Line()
+		p.advanceLine(x.Body.Pos().Line())
 		p.comments(x.Body.Comments...)
 		p.stmt(x.Body)
 	case *CaseClause:
 		p.WriteString("case ")
 		p.word(x.Word)
 		p.WriteString(" in")
+		p.advanceLine(x.In.Line())
 		p.wantSpace = spaceRequired
 		if p.swtCaseIndent {
 			p.incLevel()
@@ -1228,6 +1237,7 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 					p.wantNewline = true
 				}
 				p.spacedToken(ci.Op.String(), ci.OpPos)
+				p.advanceLine(ci.OpPos.Line())
 				// avoid ; directly after tokens like ;;
 				p.wroteSemi = true
 			}
@@ -1360,7 +1370,7 @@ func (p *Printer) stmtList(stmts []*Stmt, last []Comment) {
 		if p.mustNewline || !p.minify || p.wantSpace == spaceRequired {
 			p.newlines(pos)
 		}
-		p.line = pos.Line()
+		p.advanceLine(pos.Line())
 		p.comments(midComs...)
 		p.stmt(s)
 		p.comments(endComs...)
@@ -1420,7 +1430,7 @@ func (p *Printer) assigns(assigns []*Assign) {
 			// Ensure we don't use an escaped newline after '=',
 			// because that can result in indentation, thus
 			// splitting "foo=bar" into "foo= bar".
-			p.line = a.Value.Pos().Line()
+			p.advanceLine(a.Value.Pos().Line())
 			p.word(a.Value)
 		} else if a.Array != nil {
 			p.wantSpace = spaceNotRequired

syntax/printer_test.go

@@ -391,6 +391,14 @@ var printTests = []printCase{
 		"case $i in\n1)\n#foo \t\n;;\nesac",
 		"case $i in\n1)\n\t#foo\n\t;;\nesac",
 	},
+	{
+		"case $i in\n1)\n\t;;\n\n2)\n\t;;\nesac",
+		"case $i in\n1) ;;\n\n2) ;;\nesac",
+	},
+	{
+		"case $i\nin\n1)\n\t;;\nesac",
+		"case $i in\n1) ;;\nesac",
+	},
 	samePrint("case $i in\n1)\n\ta\n\t#b\n\t;;\nesac"),
 	samePrint("case $i in\n1) foo() { bar; } ;;\nesac"),
 	samePrint("case $i in\n1) ;; #foo\nesac"),