syntax: fix whitespace on nested subshells (#874)

we want white space on nested subshells if its in a single line since
its ambiguous, eg we want `( (` over `((`

this shouldn't be the case for multiple lines- fix the logic that adds
white space to only do so if the two subshells are in the same line

fixes #814

syntax/printer.go

@@ -1079,11 +1079,22 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 		p.ifClause(x, false)
 	case *Subshell:
 		p.WriteByte('(')
-		if len(x.Stmts) > 0 && startsWithLparen(x.Stmts[0]) {
+		stmts := x.Stmts
+		if len(stmts) > 0 && startsWithLparen(stmts[0]) {
 			p.wantSpace = spaceRequired
+			// Add a space between nested parentheses if we're printing them in a single line,
+			// to avoid the ambiguity between `((` and `( (`.
+			if (x.Lparen.Line() != stmts[0].Pos().Line() || len(stmts) > 1) && !p.singleLine {
+				p.wantSpace = spaceNotRequired
+
+				if p.minify {
+					p.mustNewline = true
+				}
+			}
 		} else {
 			p.wantSpace = spaceNotRequired
 		}
+
 		p.spacePad(stmtsPos(x.Stmts, x.Last))
 		p.nestedStmts(x.Stmts, x.Last, x.Rparen)
 		p.wantSpace = spaceNotRequired
@@ -1338,7 +1349,7 @@ func (p *Printer) stmtList(stmts []*Stmt, last []Comment) {
 			// statement.
 			p.comments(c)
 		}
-		if !p.minify || p.wantSpace == spaceRequired {
+		if p.mustNewline || !p.minify || p.wantSpace == spaceRequired {
 			p.newlines(pos)
 		}
 		p.line = pos.Line()

syntax/printer_test.go

@@ -616,6 +616,28 @@ var printTests = []printCase{
 		"`declare`",
 		"$(declare)",
 	},
+	{
+		"(\n(foo >redir))",
+		"(\n\t(foo >redir)\n)",
+	},
+	{
+		"( (foo) )",
+		"( (foo))",
+	},
+	{
+		"( (foo); bar )",
+		"(\n\t(foo)\n\tbar\n)",
+	},
+	{
+		"( ((foo++)) )",
+		"( ((foo++)))",
+	},
+	{
+		"( ((foo++)); bar )",
+		"(\n\t((foo++))\n\tbar\n)",
+	},
+	samePrint("(\n\t((foo++))\n)"),
+	samePrint("(foo && bar)"),
 }
 
 func TestPrintWeirdFormat(t *testing.T) {