Auto merge of #52375 - oli-obk:the_early_lint_pass_gets_the_worm, r=Manishearth

Lint `async` identifiers in 2018 preparation mode

r? @Manishearth

fixes #49716

Author: bors

src/librustc/lint/context.rs

@@ -327,6 +327,8 @@ pub trait EarlyLintPass: LintPass {
     fn check_lifetime(&mut self, _: &EarlyContext, _: &ast::Lifetime) { }
     fn check_path(&mut self, _: &EarlyContext, _: &ast::Path, _: ast::NodeId) { }
     fn check_attribute(&mut self, _: &EarlyContext, _: &ast::Attribute) { }
+    fn check_mac_def(&mut self, _: &EarlyContext, _: &ast::MacroDef, _id: ast::NodeId) { }
+    fn check_mac(&mut self, _: &EarlyContext, _: &ast::Mac) { }
 
     /// Called when entering a syntax node that can have lint attributes such
     /// as `#[allow(...)]`. Called with *all* the attributes of that node.
@@ -341,6 +343,8 @@ pub type EarlyLintPassObject = Box<dyn EarlyLintPass + sync::Send + sync::Sync +
 pub type LateLintPassObject = Box<dyn for<'a, 'tcx> LateLintPass<'a, 'tcx> + sync::Send
                                                                            + sync::Sync + 'static>;
 
+
+
 /// Identifies a lint known to the compiler.
 #[derive(Clone, Copy, Debug)]
 pub struct LintId {

src/librustc/lint/mod.rs

@@ -922,6 +922,10 @@ where
         return Err(CompileIncomplete::Stopped);
     }
 
+    time(sess, "pre ast expansion lint checks", || {
+        lint::check_ast_crate(sess, &krate, true)
+    });
+
     let mut resolver = Resolver::new(
         sess,
         cstore,
@@ -1134,7 +1138,7 @@ where
     });
 
     time(sess, "early lint checks", || {
-        lint::check_ast_crate(sess, &krate)
+        lint::check_ast_crate(sess, &krate, false)
     });
 
     // Discard hygiene data, which isn't required after lowering to HIR.

src/librustc_driver/driver.rs

@@ -41,6 +41,7 @@ use lint::{LintPass, LateLintPass, EarlyLintPass, EarlyContext};
 
 use std::collections::HashSet;
 
+use syntax::tokenstream::{TokenTree, TokenStream};
 use syntax::ast;
 use syntax::attr;
 use syntax::codemap::Spanned;
@@ -1784,3 +1785,70 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestFunctions {
         };
     }
 }
+
+declare_lint! {
+    pub ASYNC_IDENTS,
+    Allow,
+    "detects `async` being used as an identifier"
+}
+
+/// Checks for uses of `async` as an identifier
+#[derive(Clone)]
+pub struct Async2018;
+
+impl LintPass for Async2018 {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(ASYNC_IDENTS)
+    }
+}
+
+impl Async2018 {
+    fn check_tokens(&mut self, cx: &EarlyContext, tokens: TokenStream) {
+        for tt in tokens.into_trees() {
+            match tt {
+                TokenTree::Token(span, tok) => match tok.ident() {
+                    // only report non-raw idents
+                    Some((ident, false)) if ident.as_str() == "async" => {
+                        self.report(cx, span.substitute_dummy(ident.span))
+                    },
+                    _ => {},
+                }
+                TokenTree::Delimited(_, ref delim) => {
+                    self.check_tokens(cx, delim.tts.clone().into())
+                },
+            }
+        }
+    }
+    fn report(&mut self, cx: &EarlyContext, span: Span) {
+        // don't lint `r#async`
+        if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&span) {
+            return;
+        }
+        let mut lint = cx.struct_span_lint(
+            ASYNC_IDENTS,
+            span,
+            "`async` is a keyword in the 2018 edition",
+        );
+        lint.span_suggestion_with_applicability(
+            span,
+            "you can use a raw identifier to stay compatible",
+            "r#async".to_string(),
+            Applicability::MachineApplicable,
+        );
+        lint.emit()
+    }
+}
+
+impl EarlyLintPass for Async2018 {
+    fn check_mac_def(&mut self, cx: &EarlyContext, mac_def: &ast::MacroDef, _id: ast::NodeId) {
+        self.check_tokens(cx, mac_def.stream());
+    }
+    fn check_mac(&mut self, cx: &EarlyContext, mac: &ast::Mac) {
+        self.check_tokens(cx, mac.node.tts.clone().into());
+    }
+    fn check_ident(&mut self, cx: &EarlyContext, ident: ast::Ident) {
+        if ident.as_str() == "async" {
+            self.report(cx, ident.span);
+        }
+    }
+}

src/librustc_lint/builtin.rs

@@ -83,6 +83,14 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             )
     }
 
+    macro_rules! add_pre_expansion_builtin {
+        ($sess:ident, $($name:ident),*,) => (
+            {$(
+                store.register_early_pass($sess, false, box $name);
+                )*}
+            )
+    }
+
     macro_rules! add_early_builtin_with_new {
         ($sess:ident, $($name:ident),*,) => (
             {$(
@@ -97,6 +105,10 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             )
     }
 
+    add_pre_expansion_builtin!(sess,
+        Async2018,
+    );
+
     add_early_builtin!(sess,
                        UnusedParens,
                        UnusedImportBraces,
@@ -215,6 +227,11 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             reference: "issue #35896 <https://github.com/rust-lang/rust/issues/35896>",
             edition: Some(Edition::Edition2018),
         },
+        FutureIncompatibleInfo {
+            id: LintId::of(ASYNC_IDENTS),
+            reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
+            edition: Some(Edition::Edition2018),
+        },
         FutureIncompatibleInfo {
             id: LintId::of(SAFE_EXTERN_STATICS),
             reference: "issue #36247 <https://github.com/rust-lang/rust/issues/36247>",

src/librustc_lint/lib.rs

@@ -1,3 +1,12 @@
+error[E0453]: allow(test_lint) overruled by outer forbid(test_lint)
+  --> $DIR/lint-plugin-forbid-attrs.rs:20:9
+   |
+LL | #![forbid(test_lint)]
+   |           --------- `forbid` level set here
+...
+LL | #[allow(test_lint)]
+   |         ^^^^^^^^^ overruled by previous forbid
+
 error: item is named 'lintme'
   --> $DIR/lint-plugin-forbid-attrs.rs:18:1
    |
@@ -10,15 +19,6 @@ note: lint level defined here
 LL | #![forbid(test_lint)]
    |           ^^^^^^^^^
 
-error[E0453]: allow(test_lint) overruled by outer forbid(test_lint)
-  --> $DIR/lint-plugin-forbid-attrs.rs:20:9
-   |
-LL | #![forbid(test_lint)]
-   |           --------- `forbid` level set here
-...
-LL | #[allow(test_lint)]
-   |         ^^^^^^^^^ overruled by previous forbid
-
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0453`.

src/test/ui-fulldeps/lint-plugin-forbid-attrs.stderr

@@ -11,6 +11,7 @@
 // edition:2015
 
 #![feature(raw_identifiers)]
+#![allow(async_idents)]
 
 #[macro_export]
 macro_rules! produces_async {

src/test/ui/auxiliary/edition-kw-macro-2015.rs

@@ -11,6 +11,7 @@
 // edition:2018
 
 #![feature(raw_identifiers)]
+#![allow(async_idents)]
 
 #[macro_export]
 macro_rules! produces_async {

src/test/ui/auxiliary/edition-kw-macro-2018.rs

@@ -13,6 +13,7 @@
 // compile-pass
 
 #![feature(raw_identifiers)]
+#![allow(async_idents)]
 
 #[macro_use]
 extern crate edition_kw_macro_2015;

src/test/ui/edition-keywords-2015-2015-expansion.rs

@@ -13,6 +13,7 @@
 // compile-pass
 
 #![feature(raw_identifiers)]
+#![allow(async_idents)]
 
 #[macro_use]
 extern crate edition_kw_macro_2015;