Cleanup error messages, improve docstrings

src/librustc_lexer/src/cursor.rs

@@ -41,7 +41,7 @@ impl<'a> Cursor<'a> {
     /// If requested position doesn't exist, `EOF_CHAR` is returned.
     /// However, getting `EOF_CHAR` doesn't always mean actual end of file,
     /// it should be checked with `is_eof` method.
-    pub(crate) fn nth_char(&self, n: usize) -> char {
+    fn nth_char(&self, n: usize) -> char {
         self.chars().nth(n).unwrap_or(EOF_CHAR)
     }
 

src/librustc_lexer/src/lib.rs

@@ -141,25 +141,41 @@ pub enum LiteralKind {
     RawByteStr(UnvalidatedRawStr),
 }
 
+/// Represents something that looks like a raw string, but may have some
+/// problems. Use `.validate()` to convert it into something
+/// usable.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct UnvalidatedRawStr {
+    /// The prefix (`r###"`) is valid
     valid_start: bool,
+    /// The number of leading `#`
     n_start_hashes: usize,
+    /// The number of trailing `#`. `n_end_hashes` <= `n_start_hashes`
     n_end_hashes: usize,
+    /// The offset starting at `r` or `br` where the user may have intended to end the string.
+    /// Currently, it is the longest sequence of pattern `"#+"`.
     possible_terminator_offset: Option<usize>,
 }
 
+/// Error produced validating a raw string. Represents cases like:
+/// - `r##~"abcde"##`: `LexRawStrError::InvalidStarter`
+/// - `r###"abcde"##`: `LexRawStrError::NoTerminator { expected: 3, found: 2, possible_terminator_offset: Some(11)`
+/// - Too many `#`s (>65536): `TooManyDelimiters`
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub enum LexRawStrError {
-    /// Non # characters between `r` and `"` eg. `r#~"..`
+    /// Non `#` characters exist between `r` and `"` eg. `r#~"..`
     InvalidStarter,
-    /// The string was never terminated. `possible_terminator_offset` is the best guess of where they
+    /// The string was never terminated. `possible_terminator_offset` is the number of characters after `r` or `br` where they
     /// may have intended to terminate it.
     NoTerminator { expected: usize, found: usize, possible_terminator_offset: Option<usize> },
-    /// More than 65536 # signs
+    /// More than 65536 `#`s exist.
     TooManyDelimiters,
 }
 
+/// Raw String that contains a valid prefix (`#+"`) and postfix (`"#+`) where
+/// there are a matching number of `#` characters in both. Note that this will
+/// not consume extra trailing `#` characters: `r###"abcde"####` is lexed as a
+/// `ValidatedRawString { n_hashes: 3 }` followed by a `#` token.
 #[derive(Debug, Eq, PartialEq, Copy, Clone)]
 pub struct ValidatedRawStr {
     n_hashes: u16,
@@ -172,27 +188,26 @@ impl ValidatedRawStr {
 }
 
 impl UnvalidatedRawStr {
-    pub fn started(&self) -> bool {
-        self.valid_start
-    }
-
     pub fn validate(self) -> Result<ValidatedRawStr, LexRawStrError> {
         if !self.valid_start {
             return Err(LexRawStrError::InvalidStarter);
         }
 
+        // Only up to 65535 `#`s are allowed in raw strings
         let n_start_safe: u16 =
             self.n_start_hashes.try_into().map_err(|_| LexRawStrError::TooManyDelimiters)?;
-        match (self.n_start_hashes, self.n_end_hashes) {
-            (n_start, n_end) if n_start > n_end => Err(LexRawStrError::NoTerminator {
-                expected: n_start,
+
+        if self.n_start_hashes > self.n_end_hashes {
+            Err(LexRawStrError::NoTerminator {
+                expected: self.n_start_hashes,
                 found: self.n_end_hashes,
                 possible_terminator_offset: self.possible_terminator_offset,
-            }),
-            (n_start, n_end) => {
-                debug_assert_eq!(n_start, n_end);
-                Ok(ValidatedRawStr { n_hashes: n_start_safe })
-            }
+            })
+        } else {
+            // Since the lexer should never produce a literal with n_end > n_start, if n_start <= n_end,
+            // they must be equal.
+            debug_assert_eq!(self.n_start_hashes, self.n_end_hashes);
+            Ok(ValidatedRawStr { n_hashes: n_start_safe })
         }
     }
 }
@@ -656,7 +671,7 @@ impl Cursor<'_> {
         false
     }
 
-    /// Eats the double-quoted string an UnvalidatedRawStr
+    /// Eats the double-quoted string and returns an `UnvalidatedRawStr`.
     fn raw_double_quoted_string(&mut self, prefix_len: usize) -> UnvalidatedRawStr {
         debug_assert!(self.prev() == 'r');
         let mut valid_start: bool = false;

src/librustc_parse/lexer/mod.rs

@@ -533,13 +533,12 @@ impl<'a> StringReader<'a> {
         }
 
         if let Some(possible_offset) = possible_offset {
-            let span = self.mk_sp(
-                start + BytePos(possible_offset as u32),
-                start + BytePos(possible_offset as u32) + BytePos(found_terminators as u32),
-            );
+            let lo = start + BytePos(possible_offset as u32);
+            let hi = lo + BytePos(found_terminators as u32);
+            let span = self.mk_sp(lo, hi);
             err.span_suggestion(
                 span,
-                "you might have intended to terminate the string here",
+                "consider terminating the string here",
                 "#".repeat(n_hashes),
                 Applicability::MaybeIncorrect,
             );

src/librustc_parse/lib.rs

@@ -4,6 +4,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(bindings_after_at)]
 #![feature(try_blocks)]
+#![feature(or_patterns)]
 
 use rustc_ast::ast;
 use rustc_ast::token::{self, Nonterminal};

src/librustc_parse/parser/diagnostics.rs

@@ -288,9 +288,12 @@ impl<'a> Parser<'a> {
 
     fn check_too_many_raw_str_terminators(&mut self, err: &mut DiagnosticBuilder<'_>) -> bool {
         let prev_token_raw_str = match self.prev_token {
-            Token { kind: TokenKind::Literal(Lit { kind: LitKind::StrRaw(n), .. }), .. } => Some(n),
             Token {
-                kind: TokenKind::Literal(Lit { kind: LitKind::ByteStrRaw(n), .. }), ..
+                kind:
+                    TokenKind::Literal(Lit {
+                        kind: LitKind::StrRaw(n) | LitKind::ByteStrRaw(n), ..
+                    }),
+                ..
             } => Some(n),
             _ => None,
         };
@@ -300,11 +303,11 @@ impl<'a> Parser<'a> {
                 err.set_primary_message("too many `#` when terminating raw string");
                 err.span_suggestion(
                     self.token.span,
-                    "Remove the extra `#`",
+                    "remove the extra `#`",
                     String::new(),
                     Applicability::MachineApplicable,
                 );
-                err.note(&format!("The raw string started with {} `#`s", n_hashes));
+                err.note(&format!("the raw string started with {} `#`s", n_hashes));
                 return true;
             }
         }

src/test/ui/parser/raw/raw-byte-string-eof.stderr

@@ -2,7 +2,7 @@ error[E0748]: unterminated raw string
   --> $DIR/raw-byte-string-eof.rs:2:5
    |
 LL |     br##"a"#;
-   |     ^      - help: you might have intended to terminate the string here: `##`
+   |     ^      - help: consider terminating the string here: `##`
    |     |
    |     unterminated raw string
    |

src/test/ui/parser/raw/raw-str-unbalanced.stderr

@@ -2,9 +2,9 @@ error: too many `#` when terminating raw string
   --> $DIR/raw-str-unbalanced.rs:3:9
    |
 LL |       "##
-   |         ^ help: Remove the extra `#`
+   |         ^ help: remove the extra `#`
    |
-   = note: The raw string started with 1 `#`s
+   = note: the raw string started with 1 `#`s
 
 error: aborting due to previous error
 

src/test/ui/parser/raw/raw_string.stderr

@@ -2,7 +2,7 @@ error[E0748]: unterminated raw string
   --> $DIR/raw_string.rs:2:13
    |
 LL |     let x = r##"lol"#;
-   |             ^       - help: you might have intended to terminate the string here: `##`
+   |             ^       - help: consider terminating the string here: `##`
    |             |
    |             unterminated raw string
    |