interp: support parentheses in classic test commands

This mimics the logic in the bash test expression parser
in the syntax package, which supported them for years.

Fixes #1036.

interp/interp_test.go

@@ -1611,6 +1611,8 @@ var runTests = []runTest{
  {"set -o pipefail; [[ -o pipefail ]]", ""},
  // TODO: we don't implement precedence of && over ||.
  // {"[[ a == x && b == x || c == c ]]", ""},
+ {"[[ (a == x && b == x) || c == c ]]", ""},
+ {"[[ a == x && (b == x || c == c) ]]", "exit status 1"},
 
  // classic test
  {
@@ -1710,6 +1712,8 @@ var runTests = []runTest{
  {"[ abc != ab* ]", ""},
  // TODO: we don't implement precedence of -a over -o.
  // {"[ a = x -a b = x -o c = c ]", ""},
+ {`[ \( a = x -a b = x \) -o c = c ]`, ""},
+ {`[ a = x -a \( b = x -o c = c \) ]`, "exit status 1"},
 
  // arithm
  {

interp/test_classic.go

@@ -51,7 +51,7 @@ func (p *testParser) classicTest(fval string, pastAndOr bool) syntax.TestExpr {
  } else {
  left = p.classicTest(fval, true)
  }
- if left == nil || p.eof {
+ if left == nil || p.eof || p.val == ")" {
  return left
  }
  opStr := p.val
@@ -76,7 +76,7 @@ func (p *testParser) classicTest(fval string, pastAndOr bool) syntax.TestExpr {
 }
 
 func (p *testParser) testExprBase(fval string) syntax.TestExpr {
- if p.eof {
+ if p.eof || p.val == ")" {
  return nil
  }
  op := testUnaryOp(p.val)
@@ -86,6 +86,15 @@ func (p *testParser) testExprBase(fval string) syntax.TestExpr {
  p.next()
  u.X = p.classicTest(op.String(), false)
  return u
+ case syntax.TsParen:
+ pe := &syntax.ParenTest{}
+ p.next()
+ pe.X = p.classicTest(op.String(), false)
+ if p.val != ")" {
+ p.errf("reached %s without matching ( with )", p.val)
+ }
+ p.next()
+ return pe
  case illegalTok:
  return p.followWord(fval)
  default:
@@ -108,6 +117,8 @@ func testUnaryOp(val string) syntax.UnTestOperator {
  switch val {
  case "!":
  return syntax.TsNot
+ case "(":
+ return syntax.TsParen
  case "-e", "-a":
  return syntax.TsExists
  case "-f":

syntax/tokens.go

@@ -312,6 +312,7 @@ const (
  TsVarSet // -v
  TsRefVar // -R
  TsNot = UnTestOperator(exclMark) // !
+ TsParen = UnTestOperator(leftParen) // (
 )
 
 type BinTestOperator token