Improve compiler error for c-strings in pre-2021

Author: chfogelman

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -640,13 +640,13 @@ impl<'a> Parser<'a> {
             }
         }
 
-        // Extra info for `c"str"` before 2021 edition or `c "str"` in all editions. The heuristic
+        // Try to detect an intended c-string literal while using a pre-2021 edition. The heuristic
         // here is to identify a cooked, uninterpolated `c` id immediately followed by a string, or
-        // a cooked, uninterpolated `cr` id immediately followed by a string or a `#`, in an
-        // edition where c-string literals are not allowed. There is the slight possibility of a
-        // false positive for a `cr#` that wasn't intended to start a c-string literal, but the
-        // lexer was greedy and didn't preserve whether the `r#` on its own would have started a
-        // valid raw string literal.
+        // a cooked, uninterpolated `cr` id immediately followed by a string or a `#`, in an edition
+        // where c-string literals are not allowed. There is the very slight possibility of a false
+        // positive for a `cr#` that wasn't intended to start a c-string literal, but identifying
+        // that in the parser requires unbounded lookahead, so we only add a hint to the existing
+        // error rather than replacing it entirely.
         if ((self.prev_token.kind == TokenKind::Ident(sym::c, false)
             && matches!(&self.token.kind, TokenKind::Literal(token::Lit { kind: token::Str, .. })))
             || (self.prev_token.kind == TokenKind::Ident(sym::cr, false)
@@ -657,15 +657,9 @@ impl<'a> Parser<'a> {
             && self.prev_token.span.hi() == self.token.span.lo()
             && !self.token.span.at_least_rust_2021()
         {
-            err.cancel();
-            let descr = super::token_descr(&self.token);
-            let mut err =
-                self.struct_span_err(self.token.span, format!("found unexpected token {descr}"));
-            err.span_label(self.token.span, "found here".to_owned());
-            err.note("you may be trying to declare a c-string literal");
-            err.note("c-string literals require edition 2021 or later");
+            err.note("you may be trying to write a c-string literal");
+            err.note("c-string literals require Rust 2021 or later");
             HelpUseLatestEdition::new().add_to_diagnostic(&mut err);
-            return Err(err);
         }
 
         // `pub` may be used for an item or `pub(crate)`

tests/ui/editions/edition-cstr-2015-2018.rs

@@ -3,10 +3,10 @@ macro_rules! construct { ($x:ident) => { $x"str" } }
     //~| NOTE expected one of 8 possible tokens
 
 macro_rules! contain { () => { c"str" } }
-    //~^ ERROR found unexpected token `"str"`
-    //~| NOTE found here
-    //~| NOTE you may be trying to declare a c-string literal
-    //~| NOTE c-string literals require edition 2021 or later
+    //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+    //~| NOTE expected one of 8 possible tokens
+    //~| NOTE you may be trying to write a c-string literal
+    //~| NOTE c-string literals require Rust 2021 or later
     //~| HELP pass `--edition 2021` to `rustc`
     //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
 
@@ -25,30 +25,30 @@ fn check_macro_contain() {
 
 fn check_basic() {
     c"str";
-    //~^ ERROR found unexpected token `"str"`
-    //~| NOTE found here
-    //~| NOTE you may be trying to declare a c-string literal
-    //~| NOTE c-string literals require edition 2021 or later
+    //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+    //~| NOTE expected one of 8 possible tokens
+    //~| NOTE you may be trying to write a c-string literal
+    //~| NOTE c-string literals require Rust 2021 or later
     //~| HELP pass `--edition 2021` to `rustc`
     //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
 }
 
 fn check_craw() {
     cr"str";
-    //~^ ERROR found unexpected token `"str"`
-    //~| NOTE found here
-    //~| NOTE you may be trying to declare a c-string literal
-    //~| NOTE c-string literals require edition 2021 or later
+    //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+    //~| NOTE expected one of 8 possible tokens
+    //~| NOTE you may be trying to write a c-string literal
+    //~| NOTE c-string literals require Rust 2021 or later
     //~| HELP pass `--edition 2021` to `rustc`
     //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
 }
 
 fn check_craw_hash() {
     cr##"str"##;
-    //~^ ERROR found unexpected token `#`
-    //~| NOTE found here
-    //~| NOTE you may be trying to declare a c-string literal
-    //~| NOTE c-string literals require edition 2021 or later
+    //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `#`
+    //~| NOTE expected one of 8 possible tokens
+    //~| NOTE you may be trying to write a c-string literal
+    //~| NOTE c-string literals require Rust 2021 or later
     //~| HELP pass `--edition 2021` to `rustc`
     //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
 }

tests/ui/editions/edition-cstr-2015-2018.stderr

@@ -1,33 +1,33 @@
-error: found unexpected token `"str"`
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
   --> $DIR/edition-cstr-2015-2018.rs:27:6
    |
 LL |     c"str";
-   |      ^^^^^ found here
+   |      ^^^^^ expected one of 8 possible tokens
    |
-   = note: you may be trying to declare a c-string literal
-   = note: c-string literals require edition 2021 or later
+   = note: you may be trying to write a c-string literal
+   = note: c-string literals require Rust 2021 or later
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error: found unexpected token `"str"`
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
   --> $DIR/edition-cstr-2015-2018.rs:37:7
    |
 LL |     cr"str";
-   |       ^^^^^ found here
+   |       ^^^^^ expected one of 8 possible tokens
    |
-   = note: you may be trying to declare a c-string literal
-   = note: c-string literals require edition 2021 or later
+   = note: you may be trying to write a c-string literal
+   = note: c-string literals require Rust 2021 or later
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
-error: found unexpected token `#`
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `#`
   --> $DIR/edition-cstr-2015-2018.rs:47:7
    |
 LL |     cr##"str"##;
-   |       ^ found here
+   |       ^ expected one of 8 possible tokens
    |
-   = note: you may be trying to declare a c-string literal
-   = note: c-string literals require edition 2021 or later
+   = note: you may be trying to write a c-string literal
+   = note: c-string literals require Rust 2021 or later
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
 
@@ -48,17 +48,17 @@ LL |     construct!(c);
    |
    = note: this error originates in the macro `construct` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: found unexpected token `"str"`
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
   --> $DIR/edition-cstr-2015-2018.rs:5:33
    |
 LL | macro_rules! contain { () => { c"str" } }
-   |                                 ^^^^^ found here
+   |                                 ^^^^^ expected one of 8 possible tokens
 ...
 LL |     contain!();
    |     ---------- in this macro invocation
    |
-   = note: you may be trying to declare a c-string literal
-   = note: c-string literals require edition 2021 or later
+   = note: you may be trying to write a c-string literal
+   = note: c-string literals require Rust 2021 or later
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
    = note: this error originates in the macro `contain` (in Nightly builds, run with -Z macro-backtrace for more info)