Refine when invalid prefix case error arises

Fix cases where the "invalid base prefix for number literal" error arises with
suffixes that look erroneously capitalized but which are in fact invalid.

1 files changed, 23 insertions, 10 deletions

diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 2f7055e3cc5..268849ecd59 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -291,20 +291,33 @@ pub fn report_lit_error(sess: &ParseSess, err: LitError, lit: token::Lit, span:
         s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
     }
 
-    // Try to lowercase the prefix if it's a valid base prefix.
-    fn fix_base_capitalisation(s: &str) -> Option<String> {
-        if let Some(stripped) = s.strip_prefix('B') {
-            Some(format!("0b{stripped}"))
-        } else if let Some(stripped) = s.strip_prefix('O') {
-            Some(format!("0o{stripped}"))
-        } else if let Some(stripped) = s.strip_prefix('X') {
-            Some(format!("0x{stripped}"))
+    // Try to lowercase the prefix if the prefix and suffix are valid.
+    fn fix_base_capitalisation(prefix: &str, suffix: &str) -> Option<String> {
+        let mut chars = suffix.chars();
+
+        let base_char = chars.next().unwrap();
+        let base = match base_char {
+            'B' => 2,
+            'O' => 8,
+            'X' => 16,
+            _ => return None,
+        };
+
+        // check that the suffix contains only base-appropriate characters
+        let valid = prefix == "0"
+            && chars
+                .filter(|c| *c != '_')
+                .take_while(|c| *c != 'i' && *c != 'u')
+                .all(|c| c.to_digit(base).is_some());
+
+        if valid {
+            Some(format!("0{}{}", base_char.to_ascii_lowercase(), &suffix[1..]))
         } else {
             None
         }
     }
 
-    let token::Lit { kind, suffix, .. } = lit;
+    let token::Lit { kind, symbol, suffix, .. } = lit;
     match err {
         // `LexerError` is an error, but it was already reported
         // by lexer, so here we don't report it the second time.
@@ -324,7 +337,7 @@ pub fn report_lit_error(sess: &ParseSess, err: LitError, lit: token::Lit, span:
             if looks_like_width_suffix(&['i', 'u'], &suf) {
                 // If it looks like a width, try to be helpful.
                 sess.emit_err(InvalidIntLiteralWidth { span, width: suf[1..].into() });
-            } else if let Some(fixed) = fix_base_capitalisation(suf) {
+            } else if let Some(fixed) = fix_base_capitalisation(symbol.as_str(), suf) {
                 sess.emit_err(InvalidNumLiteralBasePrefix { span, fixed });
             } else {
                 sess.emit_err(InvalidNumLiteralSuffix { span, suffix: suf.to_string() });