Auto merge of #119156 - matthiaskrgr:rollup-482ow65, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - #118691 (Add check for possible CStr literals in pre-2021)
 - #118973 (rustc_codegen_ssa: Don't drop `IncorrectCguReuseType` , make `rustc_expected_cgu_reuse` attr work)
 - #119071 (-Znext-solver: adapt overflow rules to avoid breakage)
 - #119089 (effects: fix a comment)
 - #119094 (Add function ABI and type layout to StableMIR)
 - #119102 (Add arm-none-eabi and armv7r-none-eabi platform-support documentation.)
 - #119107 (subtype_predicate: remove unnecessary probe)

Failed merges:

 - #119135 (Fix crash due to `CrateItem::kind()` not handling constructors)
 - #119141 (Add method to get instance instantiation arguments)

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 29 insertions, 7 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 9e3637ea9f3..c077e0a83a1 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -10,13 +10,13 @@ use crate::errors::{
     ConstGenericWithoutBracesSugg, DocCommentDoesNotDocumentAnything, DocCommentOnParamType,
     DoubleColonInBound, ExpectedIdentifier, ExpectedSemi, ExpectedSemiSugg,
     GenericParamsWithoutAngleBrackets, GenericParamsWithoutAngleBracketsSugg,
-    HelpIdentifierStartsWithNumber, InInTypo, IncorrectAwait, IncorrectSemicolon,
-    IncorrectUseOfAwait, PatternMethodParamWithoutBody, QuestionMarkInType, QuestionMarkInTypeSugg,
-    SelfParamNotFirst, StructLiteralBodyWithoutPath, StructLiteralBodyWithoutPathSugg,
-    StructLiteralNeedingParens, StructLiteralNeedingParensSugg, SuggAddMissingLetStmt,
-    SuggEscapeIdentifier, SuggRemoveComma, TernaryOperator, UnexpectedConstInGenericParam,
-    UnexpectedConstParamDeclaration, UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets,
-    UseEqInstead, WrapType,
+    HelpIdentifierStartsWithNumber, HelpUseLatestEdition, InInTypo, IncorrectAwait,
+    IncorrectSemicolon, IncorrectUseOfAwait, PatternMethodParamWithoutBody, QuestionMarkInType,
+    QuestionMarkInTypeSugg, SelfParamNotFirst, StructLiteralBodyWithoutPath,
+    StructLiteralBodyWithoutPathSugg, StructLiteralNeedingParens, StructLiteralNeedingParensSugg,
+    SuggAddMissingLetStmt, SuggEscapeIdentifier, SuggRemoveComma, TernaryOperator,
+    UnexpectedConstInGenericParam, UnexpectedConstParamDeclaration,
+    UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets, UseEqInstead, WrapType,
 };
 use crate::fluent_generated as fluent;
 use crate::parser;
@@ -640,6 +640,28 @@ impl<'a> Parser<'a> {
             }
         }
 
+        // 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 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)
+                && 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 write a c-string literal");
+            err.note("c-string literals require Rust 2021 or later");
+            HelpUseLatestEdition::new().add_to_diagnostic(&mut err);
+        }
+
         // `pub` may be used for an item or `pub(crate)`
         if self.prev_token.is_ident_named(sym::public)
             && (self.token.can_begin_item()