move some invalid exponent detection into rustc_session

Author: richard-uk1

compiler/rustc_lexer/src/lib.rs

@@ -199,7 +199,7 @@ pub enum DocStyle {
 pub enum LiteralKind {
     /// `12_u8`, `0o100`, `0b120i99`, `1f32`.
     Int { base: Base, empty_int: bool },
-    /// `12.34f32`, `1e3`, but not `1f32`.
+    /// `12.34f32`, `1e3` and `1e+`, but not `1f32` or `1em`.
     Float { base: Base, empty_exponent: bool },
     /// `'a'`, `'\\'`, `'''`, `';`
     Char { terminated: bool },
@@ -361,6 +361,17 @@ pub fn is_ident(string: &str) -> bool {
     }
 }
 
+/// Is the character after the 'e' in a number valid for an exponent?
+///
+/// If not the number will be passed to the parser with a suffix beginning with 'e' rather
+/// than an exponent (and will be rejected there).
+///
+/// The way this function is written means that `1e_` is considered an invalid exponent
+/// rather than a number with suffix.
+fn is_exponent_second(ch: char) -> bool {
+    matches!(ch, '0'..='9' | '_' | '+' | '-')
+}
+
 impl Cursor<'_> {
     /// Parses a token from the input string.
     pub fn advance_token(&mut self) -> Token {
@@ -668,7 +679,7 @@ impl Cursor<'_> {
                 if self.first().is_ascii_digit() {
                     self.eat_decimal_digits();
                     match self.first() {
-                        'e' | 'E' => {
+                        'e' | 'E' if is_exponent_second(self.second()) => {
                             self.bump();
                             empty_exponent = !self.eat_float_exponent();
                         }
@@ -677,7 +688,7 @@ impl Cursor<'_> {
                 }
                 Float { base, empty_exponent }
             }
-            'e' | 'E' => {
+            'e' | 'E' if is_exponent_second(self.second()) => {
                 self.bump();
                 let empty_exponent = !self.eat_float_exponent();
                 Float { base, empty_exponent }

compiler/rustc_session/messages.ftl

@@ -18,6 +18,8 @@ session_embed_source_insufficient_dwarf_version = `-Zembed-source=y` requires at
 
 session_embed_source_requires_debug_info = `-Zembed-source=y` requires debug information to be enabled
 
+session_empty_float_exponent = expected at least one digit in exponent
+
 session_expr_parentheses_needed = parentheses are required to parse this as an expression
 
 session_failed_to_create_profiler = failed to create profiler: {$err}

compiler/rustc_session/src/errors.rs

@@ -397,6 +397,10 @@ pub fn report_lit_error(
         s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
     }
 
+    fn looks_like_exponent(s: &str) -> bool {
+        s.len() == 1 && matches!(s.chars().next(), Some('e' | 'E'))
+    }
+
     // 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();
@@ -429,6 +433,8 @@ pub fn report_lit_error(
             if looks_like_width_suffix(&['i', 'u'], suf) {
                 // If it looks like a width, try to be helpful.
                 dcx.emit_err(InvalidIntLiteralWidth { span, width: suf[1..].into() })
+            } else if looks_like_exponent(suf) {
+                dcx.emit_err(EmptyFloatExponent { span })
             } else if let Some(fixed) = fix_base_capitalisation(lit.symbol.as_str(), suf) {
                 dcx.emit_err(InvalidNumLiteralBasePrefix { span, fixed })
             } else {
@@ -440,6 +446,8 @@ pub fn report_lit_error(
             if looks_like_width_suffix(&['f'], suf) {
                 // If it looks like a width, try to be helpful.
                 dcx.emit_err(InvalidFloatLiteralWidth { span, width: suf[1..].to_string() })
+            } else if looks_like_exponent(suf) {
+                dcx.emit_err(EmptyFloatExponent { span })
             } else {
                 dcx.emit_err(InvalidFloatLiteralSuffix { span, suffix: suf.to_string() })
             }
@@ -501,3 +509,10 @@ pub(crate) struct SoftFloatIgnored;
 #[note]
 #[note(session_soft_float_deprecated_issue)]
 pub(crate) struct SoftFloatDeprecated;
+
+#[derive(Diagnostic)]
+#[diag(session_empty_float_exponent)]
+pub(crate) struct EmptyFloatExponent {
+    #[primary_span]
+    pub span: Span,
+}