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Merge visitors in AST validation #57730

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merged 2 commits into from
Jan 24, 2019
Merged

Merge visitors in AST validation #57730

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13dc584
Merge visitors in AST validation
Zoxc Jan 18, 2019
a5d4aed
Address some comments
Zoxc Jan 19, 2019
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250 changes: 106 additions & 144 deletions src/librustc_passes/ast_validation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
// This pass is supposed to perform only simple checks not requiring name resolution
// or type checking or some other kind of complex analysis.

use std::mem;
use rustc::lint;
use rustc::session::Session;
use syntax::ast::*;
Expand All @@ -20,9 +21,73 @@ use errors::Applicability;

struct AstValidator<'a> {
session: &'a Session,

// Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
// Nested `impl Trait` _is_ allowed in associated type position,
// e.g `impl Iterator<Item=impl Debug>`
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Maybe also add a note about why we do this (cause we are not sure whether we want it to be higher rank: impl for<T: Debug> Into<T>, or rank-1).

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I don't know why we do this. I just copied this comment. Feel free to suggest the exact change you'd like.

outer_impl_trait: Option<Span>,

// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
// or `Foo::Bar<impl Trait>`
is_impl_trait_banned: bool,
}

impl<'a> AstValidator<'a> {
fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.is_impl_trait_banned, true);
f(self);
self.is_impl_trait_banned = old;
}

fn with_impl_trait(&mut self, outer_impl_trait: Option<Span>, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.outer_impl_trait, outer_impl_trait);
f(self);
self.outer_impl_trait = old;
}

// Mirrors visit::walk_ty, but tracks relevant state
fn walk_ty(&mut self, t: &'a Ty) {
match t.node {
TyKind::ImplTrait(..) => {
self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
}
TyKind::Path(ref qself, ref path) => {
// We allow these:
// - `Option<impl Trait>`
// - `option::Option<impl Trait>`
// - `option::Option<T>::Foo<impl Trait>
//
// But not these:
// - `<impl Trait>::Foo`
// - `option::Option<impl Trait>::Foo`.
//
// To implement this, we disallow `impl Trait` from `qself`
// (for cases like `<impl Trait>::Foo>`)
// but we allow `impl Trait` in `GenericArgs`
// iff there are no more PathSegments.
if let Some(ref qself) = *qself {
// `impl Trait` in `qself` is always illegal
self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
}

// Note that there should be a call to visit_path here,
// so if any logic is added to process `Path`s a call to it should be
// added both in visit_path and here. This code mirrors visit::walk_path.
for (i, segment) in path.segments.iter().enumerate() {
// Allow `impl Trait` iff we're on the final path segment
if i == path.segments.len() - 1 {
self.visit_path_segment(path.span, segment);
} else {
self.with_banned_impl_trait(|this| {
this.visit_path_segment(path.span, segment)
});
}
}
}
_ => visit::walk_ty(self, t),
}
}

fn err_handler(&self) -> &errors::Handler {
&self.session.diagnostic()
}
Expand Down Expand Up @@ -267,6 +332,19 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
self.no_questions_in_bounds(bounds, "trait object types", false);
}
TyKind::ImplTrait(_, ref bounds) => {
if self.is_impl_trait_banned {
struct_span_err!(self.session, ty.span, E0667,
"`impl Trait` is not allowed in path parameters").emit();
}

if let Some(outer_impl_trait) = self.outer_impl_trait {
struct_span_err!(self.session, ty.span, E0666,
"nested `impl Trait` is not allowed")
.span_label(outer_impl_trait, "outer `impl Trait`")
.span_label(ty.span, "nested `impl Trait` here")
.emit();

}
if !bounds.iter()
.any(|b| if let GenericBound::Trait(..) = *b { true } else { false }) {
self.err_handler().span_err(ty.span, "at least one trait must be specified");
Expand All @@ -275,7 +353,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
_ => {}
}

visit::walk_ty(self, ty)
self.walk_ty(ty)
}

fn visit_label(&mut self, label: &'a Label) {
Expand Down Expand Up @@ -414,6 +492,28 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
visit::walk_foreign_item(self, fi)
}

// Mirrors visit::walk_generic_args, but tracks relevant state
fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
match *generic_args {
GenericArgs::AngleBracketed(ref data) => {
walk_list!(self, visit_generic_arg, &data.args);
// Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
// are allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| {
walk_list!(this, visit_assoc_type_binding, &data.bindings);
});
}
GenericArgs::Parenthesized(ref data) => {
walk_list!(self, visit_ty, &data.inputs);
if let Some(ref type_) = data.output {
// `-> Foo` syntax is essentially an associated type binding,
// so it is also allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| visit::walk_ty(this, type_));
}
}
}
}

fn visit_generics(&mut self, generics: &'a Generics) {
let mut seen_non_lifetime_param = false;
let mut seen_default = None;
Expand Down Expand Up @@ -490,148 +590,10 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
}
}

// Bans nested `impl Trait`, e.g., `impl Into<impl Debug>`.
// Nested `impl Trait` _is_ allowed in associated type position,
// e.g `impl Iterator<Item=impl Debug>`
struct NestedImplTraitVisitor<'a> {
session: &'a Session,
outer_impl_trait: Option<Span>,
}

impl<'a> NestedImplTraitVisitor<'a> {
fn with_impl_trait<F>(&mut self, outer_impl_trait: Option<Span>, f: F)
where F: FnOnce(&mut NestedImplTraitVisitor<'a>)
{
let old_outer_impl_trait = self.outer_impl_trait;
self.outer_impl_trait = outer_impl_trait;
f(self);
self.outer_impl_trait = old_outer_impl_trait;
}
}


impl<'a> Visitor<'a> for NestedImplTraitVisitor<'a> {
fn visit_ty(&mut self, t: &'a Ty) {
if let TyKind::ImplTrait(..) = t.node {
if let Some(outer_impl_trait) = self.outer_impl_trait {
struct_span_err!(self.session, t.span, E0666,
"nested `impl Trait` is not allowed")
.span_label(outer_impl_trait, "outer `impl Trait`")
.span_label(t.span, "nested `impl Trait` here")
.emit();

}
self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t));
} else {
visit::walk_ty(self, t);
}
}
fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
match *generic_args {
GenericArgs::AngleBracketed(ref data) => {
for arg in &data.args {
self.visit_generic_arg(arg)
}
for type_binding in &data.bindings {
// Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
// are allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| visit::walk_ty(this, &type_binding.ty));
}
}
GenericArgs::Parenthesized(ref data) => {
for type_ in &data.inputs {
self.visit_ty(type_);
}
if let Some(ref type_) = data.output {
// `-> Foo` syntax is essentially an associated type binding,
// so it is also allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| visit::walk_ty(this, type_));
}
}
}
}

fn visit_mac(&mut self, _mac: &Spanned<Mac_>) {
// covered in AstValidator
}
}

// Bans `impl Trait` in path projections like `<impl Iterator>::Item` or `Foo::Bar<impl Trait>`.
struct ImplTraitProjectionVisitor<'a> {
session: &'a Session,
is_banned: bool,
}

impl<'a> ImplTraitProjectionVisitor<'a> {
fn with_ban<F>(&mut self, f: F)
where F: FnOnce(&mut ImplTraitProjectionVisitor<'a>)
{
let old_is_banned = self.is_banned;
self.is_banned = true;
f(self);
self.is_banned = old_is_banned;
}
}

impl<'a> Visitor<'a> for ImplTraitProjectionVisitor<'a> {
fn visit_ty(&mut self, t: &'a Ty) {
match t.node {
TyKind::ImplTrait(..) => {
if self.is_banned {
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This PR will give errors about nested impl traits being banned in path parameters, unlike the old code, which doesn't visit inside impl Trait. So we'd get 3 errors then, one for nested impl Trait and one for each instance of impl Trait in a path parameter.

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SGTM.

struct_span_err!(self.session, t.span, E0667,
"`impl Trait` is not allowed in path parameters").emit();
}
}
TyKind::Path(ref qself, ref path) => {
// We allow these:
// - `Option<impl Trait>`
// - `option::Option<impl Trait>`
// - `option::Option<T>::Foo<impl Trait>
//
// But not these:
// - `<impl Trait>::Foo`
// - `option::Option<impl Trait>::Foo`.
//
// To implement this, we disallow `impl Trait` from `qself`
// (for cases like `<impl Trait>::Foo>`)
// but we allow `impl Trait` in `GenericArgs`
// iff there are no more PathSegments.
if let Some(ref qself) = *qself {
// `impl Trait` in `qself` is always illegal
self.with_ban(|this| this.visit_ty(&qself.ty));
}

for (i, segment) in path.segments.iter().enumerate() {
// Allow `impl Trait` iff we're on the final path segment
if i == path.segments.len() - 1 {
visit::walk_path_segment(self, path.span, segment);
} else {
self.with_ban(|this|
visit::walk_path_segment(this, path.span, segment));
}
}
}
_ => visit::walk_ty(self, t),
}
}

fn visit_mac(&mut self, _mac: &Spanned<Mac_>) {
// covered in AstValidator
}
}

pub fn check_crate(session: &Session, krate: &Crate) {
visit::walk_crate(
&mut NestedImplTraitVisitor {
session,
outer_impl_trait: None,
}, krate);

visit::walk_crate(
&mut ImplTraitProjectionVisitor {
session,
is_banned: false,
}, krate);

visit::walk_crate(&mut AstValidator { session }, krate)
visit::walk_crate(&mut AstValidator {
session,
outer_impl_trait: None,
is_impl_trait_banned: false,
}, krate)
}