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pprust: Add parentheses to some Expr

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Some `Expr` needs parentheses when printed. For example, without
parentheses, `ExprUnary(UnNeg, ExprBinary(BiAdd, ..))` becomes
`-lhs + rhs` which is wrong.

Those cases don't appear in ordinary code (since parentheses are
explicitly added) but they can appear in manually crafted ast by
extensions.
This commit is contained in:
klutzy 2014-04-17 05:33:58 +09:00 committed by Alex Crichton
parent 6d535b5b8d
commit 7f203b6955
1 changed files with 45 additions and 3 deletions
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48
src/libsyntax/print/pprust.rs
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@ -247,6 +247,15 @@ pub fn visibility_qualified(vis: ast::Visibility, s: &str) -> StrBuf {
}
}
fn needs_parentheses(expr: &ast::Expr) -> bool {
match expr.node {
ast::ExprAssign(..) | ast::ExprBinary(..) |
ast::ExprFnBlock(..) | ast::ExprProc(..) |
ast::ExprAssignOp(..) | ast::ExprCast(..) => true,
_ => false,
}
}
impl<'a> State<'a> {
pub fn ibox(&mut self, u: uint) -> IoResult<()> {
self.boxes.push(pp::Inconsistent);
@ -1136,6 +1145,18 @@ impl<'a> State<'a> {
self.pclose()
}
pub fn print_expr_maybe_paren(&mut self, expr: &ast::Expr) -> IoResult<()> {
let needs_par = needs_parentheses(expr);
if needs_par {
try!(self.popen());
}
try!(self.print_expr(expr));
if needs_par {
try!(self.pclose());
}
Ok(())
}
pub fn print_expr(&mut self, expr: &ast::Expr) -> IoResult<()> {
try!(self.maybe_print_comment(expr.span.lo));
try!(self.ibox(indent_unit));
@ -1209,7 +1230,7 @@ impl<'a> State<'a> {
try!(self.pclose());
}
ast::ExprCall(func, ref args) => {
try!(self.print_expr(func));
try!(self.print_expr_maybe_paren(func));
try!(self.print_call_post(args.as_slice()));
}
ast::ExprMethodCall(ident, ref tys, ref args) => {
@ -1233,17 +1254,38 @@ impl<'a> State<'a> {
}
ast::ExprUnary(op, expr) => {
try!(word(&mut self.s, ast_util::unop_to_str(op)));
try!(self.print_expr(expr));
try!(self.print_expr_maybe_paren(expr));
}
ast::ExprAddrOf(m, expr) => {
try!(word(&mut self.s, "&"));
// `ExprAddrOf(ExprLit("str"))` should be `&&"str"` instead of `&"str"`
// since `&"str"` is `ExprVstore(ExprLit("str"))` which has same meaning to
// `"str"`.
// In many cases adding parentheses (`&("str")`) would help, but it become invalid
// if expr is in `PatLit()`.
let needs_extra_amp = match expr.node {
ast::ExprLit(lit) => {
match lit.node {
ast::LitStr(..) => true,
_ => false,
}
}
ast::ExprVec(..) => true,
_ => false,
};
if needs_extra_amp {
try!(word(&mut self.s, "&"));
}
try!(self.print_mutability(m));
// Avoid `& &e` => `&&e`.
match (m, &expr.node) {
(ast::MutImmutable, &ast::ExprAddrOf(..)) => try!(space(&mut self.s)),
_ => { }
}
try!(self.print_expr(expr));
try!(self.print_expr_maybe_paren(expr));
}
ast::ExprLit(lit) => try!(self.print_literal(lit)),
ast::ExprCast(expr, ty) => {