Redo improvement to c-string literal errors in pre-2021

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -640,15 +640,32 @@ impl<'a> Parser<'a> {
             }
         }
 
-        // extra info for `c"str"` before 2021 edition or `c "str"` in all editions
-        if self.prev_token.is_ident_named(Symbol::intern("c"))
-            && let TokenKind::Literal(token::Lit { kind: token::Str | token::StrRaw(..), .. }) =
-                &self.token.kind
+        // Extra info for `c"str"` before 2021 edition or `c "str"` in all editions. 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.
+        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)
+                && matches!(
+                    &self.token.kind,
+                    TokenKind::Literal(token::Lit { kind: token::Str, .. }) | token::Pound
+                )))
+            && self.prev_token.span.hi() == self.token.span.lo()
+            && !self.token.span.at_least_rust_2021()
         {
-            err.note("you may be trying to declare a CStr literal");
-            err.note("`CStr` literals require edition 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");
             HelpUseLatestEdition::new().add_to_diagnostic(&mut err);
-            err.note("`c` modifier in CStr literal cannot be followed by whitespace");
+            return Err(err);
         }
 
         // `pub` may be used for an item or `pub(crate)`

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

@@ -1,10 +1,62 @@
-fn main() {
-    c"str";
+macro_rules! construct { ($x:ident) => { $x"str" } }
     //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
     //~| NOTE expected one of 8 possible tokens
-    //~| NOTE you may be trying to declare a CStr literal
-    //~| NOTE `CStr` literals require edition 2021
+
+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
+    //~| HELP pass `--edition 2021` to `rustc`
+    //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
+
+fn check_macro_construct() {
+    construct!(c); //~ NOTE in this expansion of construct!
+}
+
+fn check_macro_contain() {
+    contain!();
+    //~^ NOTE in this expansion of contain!
+    //~| NOTE in this expansion of contain!
+    //~| NOTE in this expansion of contain!
+    //~| NOTE in this expansion of contain!
+    //~| NOTE in this expansion of 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
     //~| HELP pass `--edition 2021` to `rustc`
     //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
-    //~| NOTE `c` modifier in CStr literal cannot be followed by whitespace
 }
+
+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
+    //~| 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
+    //~| HELP pass `--edition 2021` to `rustc`
+    //~| NOTE for more on editions, read https://doc.rust-lang.org/edition-guide
+}
+
+fn check_cstr_space() {
+    c "str";
+    //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+    //~| NOTE expected one of 8 possible tokens
+}
+
+fn main() {}

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

@@ -1,14 +1,67 @@
-error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
-  --> $DIR/edition-cstr-2015-2018.rs:2:6
+error: found unexpected token `"str"`
+  --> $DIR/edition-cstr-2015-2018.rs:27:6
    |
 LL |     c"str";
-   |      ^^^^^ expected one of 8 possible tokens
+   |      ^^^^^ found here
+   |
+   = note: you may be trying to declare a c-string literal
+   = note: c-string literals require edition 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"`
+  --> $DIR/edition-cstr-2015-2018.rs:37:7
+   |
+LL |     cr"str";
+   |       ^^^^^ found here
+   |
+   = note: you may be trying to declare a c-string literal
+   = note: c-string literals require edition 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 `#`
+  --> $DIR/edition-cstr-2015-2018.rs:47:7
+   |
+LL |     cr##"str"##;
+   |       ^ found here
+   |
+   = note: you may be trying to declare a c-string literal
+   = note: c-string literals require edition 2021 or later
+   = help: pass `--edition 2021` to `rustc`
+   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
+
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+  --> $DIR/edition-cstr-2015-2018.rs:57:7
+   |
+LL |     c "str";
+   |       ^^^^^ expected one of 8 possible tokens
+
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `"str"`
+  --> $DIR/edition-cstr-2015-2018.rs:1:44
+   |
+LL | macro_rules! construct { ($x:ident) => { $x"str" } }
+   |                                            ^^^^^ expected one of 8 possible tokens
+...
+LL |     construct!(c);
+   |     ------------- in this macro invocation
+   |
+   = note: this error originates in the macro `construct` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: found unexpected token `"str"`
+  --> $DIR/edition-cstr-2015-2018.rs:5:33
+   |
+LL | macro_rules! contain { () => { c"str" } }
+   |                                 ^^^^^ found here
+...
+LL |     contain!();
+   |     ---------- in this macro invocation
    |
-   = note: you may be trying to declare a CStr literal
-   = note: `CStr` literals require edition 2021
+   = note: you may be trying to declare a c-string literal
+   = note: c-string literals require edition 2021 or later
    = help: pass `--edition 2021` to `rustc`
    = note: for more on editions, read https://doc.rust-lang.org/edition-guide
-   = note: `c` modifier in CStr literal cannot be followed by whitespace
+   = note: this error originates in the macro `contain` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 1 previous error
+error: aborting due to 6 previous errors