From 19967c5890851148800886e3770fb45fb4b9ff90 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 15 May 2023 16:41:32 +1000
Subject: [PATCH 1/2] Make `Cursor::number` less DRY.

A tiny bit of repetition makes this easier to read, and avoids a test on
the "Not a base prefix" match arm.
---
 compiler/rustc_lexer/src/lib.rs | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/compiler/rustc_lexer/src/lib.rs b/compiler/rustc_lexer/src/lib.rs
index c07dc19a0ac..30b7686314e 100644
--- a/compiler/rustc_lexer/src/lib.rs
+++ b/compiler/rustc_lexer/src/lib.rs
@@ -582,34 +582,34 @@ impl Cursor<'_> {
         let mut base = Base::Decimal;
         if first_digit == '0' {
             // Attempt to parse encoding base.
-            let has_digits = match self.first() {
+            match self.first() {
                 'b' => {
                     base = Base::Binary;
                     self.bump();
-                    self.eat_decimal_digits()
+                    if !self.eat_decimal_digits() {
+                        return Int { base, empty_int: true };
+                    }
                 }
                 'o' => {
                     base = Base::Octal;
                     self.bump();
-                    self.eat_decimal_digits()
+                    if !self.eat_decimal_digits() {
+                        return Int { base, empty_int: true };
+                    }
                 }
                 'x' => {
                     base = Base::Hexadecimal;
                     self.bump();
-                    self.eat_hexadecimal_digits()
+                    if !self.eat_hexadecimal_digits() {
+                        return Int { base, empty_int: true };
+                    }
                 }
                 // Not a base prefix.
                 '0'..='9' | '_' | '.' | 'e' | 'E' => {
                     self.eat_decimal_digits();
-                    true
                 }
                 // Just a 0.
                 _ => return Int { base, empty_int: false },
-            };
-            // Base prefix was provided, but there were no digits
-            // after it, e.g. "0x".
-            if !has_digits {
-                return Int { base, empty_int: true };
             }
         } else {
             // No base prefix, parse number in the usual way.

From e52794decda5e55d730436bb38c06958a117e2c8 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 15 May 2023 16:53:57 +1000
Subject: [PATCH 2/2] Don't try to eat non-existent decimal digits.

After seeing a `0`, if it's followed by any of `[0-9]`, `_`, `.`, `e`,
or `E`, we consume all the digits. But in the `.`, `e` and `E` cases
this is pointless because we know there aren't any digits.
---
 compiler/rustc_lexer/src/lib.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_lexer/src/lib.rs b/compiler/rustc_lexer/src/lib.rs
index 30b7686314e..d511d2b1280 100644
--- a/compiler/rustc_lexer/src/lib.rs
+++ b/compiler/rustc_lexer/src/lib.rs
@@ -604,10 +604,14 @@ impl Cursor<'_> {
                         return Int { base, empty_int: true };
                     }
                 }
-                // Not a base prefix.
-                '0'..='9' | '_' | '.' | 'e' | 'E' => {
+                // Not a base prefix; consume additional digits.
+                '0'..='9' | '_' => {
                     self.eat_decimal_digits();
                 }
+
+                // Also not a base prefix; nothing more to do here.
+                '.' | 'e' | 'E' => {}
+
                 // Just a 0.
                 _ => return Int { base, empty_int: false },
             }