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Parse & reject postfix operators after casts #68985

Merged
merged 12 commits into from
Mar 7, 2020
72 changes: 67 additions & 5 deletions src/librustc_parse/parser/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -551,8 +551,8 @@ impl<'a> Parser<'a> {
// Save the state of the parser before parsing type normally, in case there is a
// LessThan comparison after this cast.
let parser_snapshot_before_type = self.clone();
match self.parse_ty_no_plus() {
Ok(rhs) => Ok(mk_expr(self, rhs)),
let cast_expr = match self.parse_ty_no_plus() {
Ok(rhs) => mk_expr(self, rhs),
Err(mut type_err) => {
// Rewind to before attempting to parse the type with generics, to recover
// from situations like `x as usize < y` in which we first tried to parse
Expand Down Expand Up @@ -606,17 +606,79 @@ impl<'a> Parser<'a> {
)
.emit();

Ok(expr)
expr
}
Err(mut path_err) => {
// Couldn't parse as a path, return original error and parser state.
path_err.cancel();
mem::replace(self, parser_snapshot_after_type);
Err(type_err)
return Err(type_err);
}
}
}
}
};

self.parse_and_disallow_postfix_after_cast(cast_expr)
}

/// Parses a postfix operators such as `.`, `?`, or index (`[]`) after a cast,
/// then emits an error and returns the newly parsed tree.
/// The resulting parse tree for `&x as T[0]` has a precedence of `((&x) as T)[0]`.
fn parse_and_disallow_postfix_after_cast(
&mut self,
cast_expr: P<Expr>,
) -> PResult<'a, P<Expr>> {
use std::collections::hash_map::DefaultHasher;
use std::hash::Hasher;
// Hash the memory location of expr before parsing any following postfix operators.
// This will be compared with the hash of the output expression.
// If they different we can assume we parsed another expression because the existing expression is not reallocated.
let mut before_hasher = DefaultHasher::new();
std::ptr::hash(&*cast_expr, &mut before_hasher);
let before_hash = before_hasher.finish();
let span = cast_expr.span;
let with_postfix = self.parse_dot_or_call_expr_with_(cast_expr, span)?;

let mut after_hasher = DefaultHasher::new();
std::ptr::hash(&*with_postfix, &mut after_hasher);
let after_hash = after_hasher.finish();
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// Check if an illegal postfix operator has been added after the cast.
// If the resulting expression is not a cast, or has a different memory location, it is an illegal postfix operator.
if !matches!(with_postfix.kind, ExprKind::Cast(_, _) | ExprKind::Type(_, _))
|| after_hash != before_hash
{
let msg = format!(
"casts cannot be followed by {}",
match with_postfix.kind {
ExprKind::Index(_, _) => "indexing",
ExprKind::Try(_) => "?",
ExprKind::Field(_, _) => "a field access",
ExprKind::MethodCall(_, _) => "a method call",
ExprKind::Call(_, _) => "a function call",
ExprKind::Await(_) => "`.await`",
_ => unreachable!("parse_dot_or_call_expr_with_ shouldn't produce this"),
}
);
let mut err = self.struct_span_err(span, &msg);
// if type ascription is "likely an error", the user will already be getting a useful
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// help message, and doesn't need a second.
if self.last_type_ascription.map_or(false, |last_ascription| last_ascription.1) {
self.maybe_annotate_with_ascription(&mut err, false);
} else {
let suggestions = vec![
(span.shrink_to_lo(), "(".to_string()),
(span.shrink_to_hi(), ")".to_string()),
];
err.multipart_suggestion(
"try surrounding the expression in parentheses",
suggestions,
Applicability::MachineApplicable,
);
}
err.emit();
};
Ok(with_postfix)
}

fn parse_assoc_op_ascribe(&mut self, lhs: P<Expr>, lhs_span: Span) -> PResult<'a, P<Expr>> {
Expand Down
171 changes: 171 additions & 0 deletions src/test/ui/parser/issue-35813-postfix-after-cast.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,171 @@
// edition:2018
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#![crate_type = "lib"]
#![feature(type_ascription)]
use std::future::Future;
use std::pin::Pin;

// This tests the parser for "x as Y[z]". It errors, but we want to give useful
// errors and parse such that further code gives useful errors.
pub fn index_after_as_cast() {
vec![1, 2, 3] as Vec<i32>[0];
//~^ ERROR: casts cannot be followed by indexing
vec![1, 2, 3]: Vec<i32>[0];
//~^ ERROR: casts cannot be followed by indexing
}

pub fn index_after_cast_to_index() {
(&[0]) as &[i32][0];
//~^ ERROR: casts cannot be followed by indexing
(&[0i32]): &[i32; 1][0];
//~^ ERROR: casts cannot be followed by indexing
}

pub fn cast_after_cast() {
if 5u64 as i32 as u16 == 0u16 {

}
if 5u64: u64: u64 == 0u64 {

}
let _ = 5u64: u64: u64 as u8 as i8 == 9i8;
let _ = 0i32: i32: i32;
let _ = 0 as i32: i32;
let _ = 0i32: i32 as i32;
let _ = 0 as i32 as i32;
let _ = 0i32: i32: i32 as u32 as i32;
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}

pub fn cast_cast_method_call() {
let _ = 0i32: i32: i32.count_ones();
//~^ ERROR: casts cannot be followed by a method call
let _ = 0 as i32: i32.count_ones();
//~^ ERROR: casts cannot be followed by a method call
let _ = 0i32: i32 as i32.count_ones();
//~^ ERROR: casts cannot be followed by a method call
let _ = 0 as i32 as i32.count_ones();
//~^ ERROR: casts cannot be followed by a method call
let _ = 0i32: i32: i32 as u32 as i32.count_ones();
//~^ ERROR: casts cannot be followed by a method call
let _ = 0i32: i32.count_ones(): u32;
//~^ ERROR: casts cannot be followed by a method call
let _ = 0 as i32.count_ones(): u32;
//~^ ERROR: casts cannot be followed by a method call
let _ = 0i32: i32.count_ones() as u32;
//~^ ERROR: casts cannot be followed by a method call
let _ = 0 as i32.count_ones() as u32;
//~^ ERROR: casts cannot be followed by a method call
let _ = 0i32: i32: i32.count_ones() as u32 as i32;
//~^ ERROR: casts cannot be followed by a method call
}

pub fn multiline_error() {
let _ = 0
as i32
.count_ones();
//~^^^ ERROR: casts cannot be followed by a method call
}

// this tests that the precedence for `!x as Y.Z` is still what we expect
pub fn precedence() {
let x: i32 = &vec![1, 2, 3] as &Vec<i32>[0];
//~^ ERROR: casts cannot be followed by indexing
}

pub fn method_calls() {
0 as i32.max(0);
//~^ ERROR: casts cannot be followed by a method call
0: i32.max(0);
//~^ ERROR: casts cannot be followed by a method call
}

pub fn complex() {
let _ = format!(
"{} and {}",
if true { 33 } else { 44 } as i32.max(0),
//~^ ERROR: casts cannot be followed by a method call
if true { 33 } else { 44 }: i32.max(0)
//~^ ERROR: casts cannot be followed by a method call
);
}

pub fn in_condition() {
if 5u64 as i32.max(0) == 0 {
//~^ ERROR: casts cannot be followed by a method call
}
if 5u64: u64.max(0) == 0 {
//~^ ERROR: casts cannot be followed by a method call
}
}

pub fn inside_block() {
let _ = if true {
5u64 as u32.max(0) == 0
//~^ ERROR: casts cannot be followed by a method call
} else { false };
let _ = if true {
5u64: u64.max(0) == 0
//~^ ERROR: casts cannot be followed by a method call
} else { false };
}

static bar: &[i32] = &(&[1,2,3] as &[i32][0..1]);
//~^ ERROR: casts cannot be followed by indexing

static bar2: &[i32] = &(&[1i32,2,3]: &[i32; 3][0..1]);
//~^ ERROR: casts cannot be followed by indexing


pub fn cast_then_try() -> Result<u64,u64> {
Err(0u64) as Result<u64,u64>?;
//~^ ERROR: casts cannot be followed by ?
Err(0u64): Result<u64,u64>?;
//~^ ERROR: casts cannot be followed by ?
Ok(1)
}


pub fn cast_then_call() {
type F = fn(u8);
// type ascription won't actually do [unique drop fn type] -> fn(u8) casts.
let drop_ptr = drop as fn(u8);
drop as F();
//~^ ERROR: parenthesized type parameters may only be used with a `Fn` trait [E0214]
drop_ptr: F();
//~^ ERROR: parenthesized type parameters may only be used with a `Fn` trait [E0214]
}

pub fn cast_to_fn_should_work() {
let drop_ptr = drop as fn(u8);
drop as fn(u8);
drop_ptr: fn(u8);
}

pub fn parens_after_cast_error() {
let drop_ptr = drop as fn(u8);
drop as fn(u8)(0);
//~^ ERROR: casts cannot be followed by a function call
drop_ptr: fn(u8)(0);
//~^ ERROR: casts cannot be followed by a function call
}

pub async fn cast_then_await() {
Box::pin(noop()) as Pin<Box<dyn Future<Output = ()>>>.await;
//~^ ERROR: casts cannot be followed by `.await`

Box::pin(noop()): Pin<Box<_>>.await;
//~^ ERROR: casts cannot be followed by `.await`
}

pub async fn noop() {}

#[derive(Default)]
pub struct Foo {
pub bar: u32,
}

pub fn struct_field() {
Foo::default() as Foo.bar;
//~^ ERROR: cannot be followed by a field access
Foo::default(): Foo.bar;
//~^ ERROR: cannot be followed by a field access
}
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