fix(parser): handle leading-zero numeric exponents (#28295)

Leading-zero exponent paths skipped the numeric-literal boundary check,
and valid uppercase exponents were rejected. Apply the same grammar
rules in the parser and standalone lexer.

AI-assisted implementation.

crates/oxc_lexer/src/diagnostics.rs

@@ -82,8 +82,8 @@ enum NumErr {
 
 /// Port of oxc_parser's numeric scanner (`lexer/numeric.rs`), stopping at
 /// its first diagnostic. Mirrors the quirks exactly: no separators in
-/// legacy-octal-like decimals, a legacy-octal exponent only as lowercase `e`
-/// after an `8`/`9` flipped the run to NonOctalDecimal, and `.` after a
+/// legacy-octal-like decimals, an exponent only after an `8`/`9` flipped
+/// the run to NonOctalDecimal, and `.` after a
 /// pure-octal run simply ends the token. Each method notes the parser
 /// function it ports.
 struct NumericWalk<'a> {
@@ -131,11 +131,10 @@ impl NumericWalk<'_> {
             Some(b'b' | b'B') => self.non_decimal(|c| matches!(c, b'0' | b'1')),
             Some(b'o' | b'O') => self.non_decimal(|c| matches!(c, b'0'..=b'7')),
             Some(b'x' | b'X') => self.non_decimal(u8::is_ascii_hexdigit),
-            // `0e...`: the parser returns straight out of the exponent read -
-            // no trailing-char check on this path.
             Some(b'e' | b'E') => {
                 self.bump();
-                self.exponent()
+                self.exponent()?;
+                self.check_after()
             }
             Some(b'.') => {
                 self.bump();
@@ -196,10 +195,10 @@ impl NumericWalk<'_> {
                 self.bump();
                 self.optional_fraction_then_exponent()
             }
-            // Lowercase only, faithfully: the parser rejects `08E1`.
-            Some(b'e') if decimal => {
+            Some(b'e' | b'E') if decimal => {
                 self.bump();
-                self.exponent()
+                self.exponent()?;
+                self.check_after()
             }
             _ => self.check_after(),
         }

crates/oxc_lexer/src/pipeline/lanes.rs

@@ -758,8 +758,8 @@ fn validate_number(src: &[u8], s: usize, e: usize) -> DiagCode {
 
         // Legacy-octal-like decimal (leading `0` + digit/`_`): oxc_parser
         // consumes only `[0-9]` for the integer part - no separators, no bigint suffix -
-        // and accepts an exponent only as lowercase `e` after an `8`/`9` flipped
-        // the run to NonOctalDecimal (`08e1` valid; `00e1` and `08E1` not).
+        // and accepts an exponent after an `8`/`9` flipped the run to
+        // NonOctalDecimal (`08e1` and `08E1` valid; `00e1` not).
         // Bare `00`/`08` are valid sloppy-mode Annex B, and `.` never flags.
         if matches!(body[1], b'0'..=b'9' | b'_') {
             // Only the integer part is checked here. A fraction or exponent after an `8`/`9`
@@ -773,9 +773,9 @@ fn validate_number(src: &[u8], s: usize, e: usize) -> DiagCode {
             }
             let run = bytes.iter().take_while(|c| c.is_ascii_digit()).count();
             match bytes.get(run) {
-                // `08e1`: valid NonOctalDecimal exponent; its digits are
+                // `08e1` / `08E1`: valid NonOctalDecimal exponent; its digits are
                 // still checked below (`08e` stays flagged).
-                Some(&b'e') if bytes[..run].iter().any(|&c| c >= b'8') => {}
+                Some(&b'e' | &b'E') if bytes[..run].iter().any(|&c| c >= b'8') => {}
                 Some(&b'e' | &b'E') => return DiagCode::InvalidNumericLiteral,
                 _ => {}
             }

crates/oxc_lexer/tests/diagnostics.rs

@@ -92,8 +92,7 @@ fn numeric_separator_and_empty_radix() {
 #[test]
 fn legacy_octal_like_decimal() {
     // Leading `0` + digit: no separators in the integer part, no bigint suffix,
-    // and an exponent only as lowercase `e` after an 8/9
-    // (oxc_parser's `read_legacy_octal` quirk).
+    // and an exponent only after an 8/9.
     assert_eq!(codes("x = 0_0;"), [DiagCode::InvalidNumericSeparator]);
     assert_eq!(codes("x = 00_0;"), [DiagCode::InvalidNumericSeparator]);
     assert_eq!(codes("x = 08_0;"), [DiagCode::InvalidNumericSeparator]);
@@ -101,7 +100,7 @@ fn legacy_octal_like_decimal() {
     assert_eq!(codes("x = 08n;"), [DiagCode::InvalidBigint]);
     assert_eq!(codes("x = 0008n;"), [DiagCode::InvalidBigint]);
     assert_eq!(codes("x = 00e1;"), [DiagCode::InvalidNumericLiteral]);
-    assert_eq!(codes("x = 08E1;"), [DiagCode::InvalidNumericLiteral]);
+    assert_eq!(codes("x = 08E1;"), []);
 }
 
 #[test]

crates/oxc_parser/src/lexer/numeric.rs

@@ -13,7 +13,8 @@ impl<C: Config> Lexer<'_, C> {
             Some(b'x' | b'X') => self.read_non_decimal(Kind::Hex),
             Some(b'e' | b'E') => {
                 self.consume_char();
-                self.read_decimal_exponent()
+                let kind = self.read_decimal_exponent();
+                self.check_after_numeric_literal(kind)
             }
             Some(b'.') => {
                 self.consume_char();
@@ -117,10 +118,11 @@ impl<C: Config> Lexer<'_, C> {
                 self.consume_char();
                 self.decimal_literal_after_decimal_point_after_digits()
             }
-            // allow 08e1 and 09e1
-            Some(b'e') if kind == Kind::Decimal => {
+            // allow 08e1, 09e1, and their uppercase exponent forms
+            Some(b'e' | b'E') if kind == Kind::Decimal => {
                 self.consume_char();
-                self.read_decimal_exponent()
+                let kind = self.read_decimal_exponent();
+                self.check_after_numeric_literal(kind)
             }
             _ => self.check_after_numeric_literal(kind),
         }

tasks/coverage/misc/fail/numeric-exponent-legacy-follow.cjs

@@ -0,0 +1 @@
+08e1in {};

tasks/coverage/misc/fail/numeric-exponent-zero-follow.js

@@ -0,0 +1 @@
+0e1in {};

tasks/coverage/misc/pass/numeric-exponent-uppercase.cjs

@@ -0,0 +1 @@
+const values = [08E1, 09E+2, 008E-1, 078E2, 0009E0, 080E-2];

tasks/coverage/snapshots/codegen_misc.snap

@@ -1,3 +1,3 @@
 codegen_misc Summary:
-AST Parsed     : 119/119 (100.00%)
-Positive Passed: 119/119 (100.00%)
+AST Parsed     : 120/120 (100.00%)
+Positive Passed: 120/120 (100.00%)

tasks/coverage/snapshots/formatter_misc.snap

@@ -1,3 +1,3 @@
 formatter_misc Summary:
-AST Parsed     : 119/119 (100.00%)
-Positive Passed: 119/119 (100.00%)
+AST Parsed     : 120/120 (100.00%)
+Positive Passed: 120/120 (100.00%)

tasks/coverage/snapshots/lexer_misc.snap

@@ -1,3 +1,3 @@
 lexer_misc Summary:
-AST Parsed     : 374/374 (100.00%)
-Positive Passed: 374/374 (100.00%)
+AST Parsed     : 377/377 (100.00%)
+Positive Passed: 377/377 (100.00%)

tasks/coverage/snapshots/parser_babel.snap

@@ -8338,6 +8338,13 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  2 │ 09.5e-_1;
    ╰────
 
+  × Invalid characters after number
+   ╭─[babel/packages/babel-parser/test/fixtures/es2021/numeric-separator/invalid-separator-after-exponent-sign-non-octal-decimal/input.js:1:5]
+ 1 │ 08e+_1;
+   ·     ─
+ 2 │ 09.5e-_1;
+   ╰────
+
   × Invalid Character `_`
    ╭─[babel/packages/babel-parser/test/fixtures/es2021/numeric-separator/invalid-separator-before-exponent-sign/input.js:1:3]
  1 │ 1e_+1;
@@ -13672,12 +13679,11 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Add an initializer (e.g. ` = undefined`) here
 
-  × Expected a semicolon or an implicit semicolon after a statement, but found none
+  × Invalid characters after number
    ╭─[babel/packages/babel-parser/test/fixtures/estree/bigInt/invalid-float/input.js:1:4]
  1 │ 0e0n;
-   ·    ▲
+   ·    ─
    ╰────
-  help: Try inserting a semicolon here
 
   × TS(18019): 'abstract' modifier cannot be used with a private identifier.
    ╭─[babel/packages/babel-parser/test/fixtures/estree/class-private-property/typescript-invalid-abstract/input.ts:2:3]

tasks/coverage/snapshots/parser_misc.snap

@@ -1,7 +1,7 @@
 parser_misc Summary:
-AST Parsed     : 119/119 (100.00%)
-Positive Passed: 119/119 (100.00%)
-Negative Passed: 257/257 (100.00%)
+AST Parsed     : 120/120 (100.00%)
+Positive Passed: 120/120 (100.00%)
+Negative Passed: 259/259 (100.00%)
 
   × TS(1275): 'accessor' modifier can only appear on a property declaration.
    ╭─[misc/fail/accessor-modifier-abstract-method.ts:1:29]
@@ -1347,6 +1347,18 @@ Negative Passed: 257/257 (100.00%)
    ·               ╰── Conditional starts here
    ╰────
 
+  × Invalid characters after number
+   ╭─[misc/fail/numeric-exponent-legacy-follow.cjs:1:5]
+ 1 │ 08e1in {};
+   ·     ──
+   ╰────
+
+  × Invalid characters after number
+   ╭─[misc/fail/numeric-exponent-zero-follow.js:1:4]
+ 1 │ 0e1in {};
+   ·    ──
+   ╰────
+
   × Identifier `b` has already been declared
    ╭─[misc/fail/oxc-10159.js:1:22]
  1 │ function a() { class b { }; function b() { } }

tasks/coverage/snapshots/parser_test262.snap

@@ -22809,13 +22809,12 @@ Negative Passed: 4653/4653 (100.00%)
     ·   ▲
     ╰────
 
-  × Expected a semicolon or an implicit semicolon after a statement, but found none
+  × Invalid characters after number
     ╭─[test262/test/language/literals/bigint/exponent-part.js:17:4]
  16 │ 
  17 │ 0e0n;
-    ·    ▲
+    ·    ─
     ╰────
-  help: Try inserting a semicolon here
 
   × Invalid Character `g`
     ╭─[test262/test/language/literals/bigint/hexadecimal-invalid-digit.js:27:3]

tasks/coverage/snapshots/semantic_misc.snap

@@ -1,6 +1,6 @@
 semantic_misc Summary:
-AST Parsed     : 119/119 (100.00%)
-Positive Passed: 113/119 (94.96%)
+AST Parsed     : 120/120 (100.00%)
+Positive Passed: 114/120 (95.00%)
 semantic Error: tasks/coverage/misc/pass/declare-let-private.ts
 Bindings mismatch:
 after transform: ScopeId(0): ["private"]

tasks/coverage/snapshots/transformer_misc.snap

@@ -1,3 +1,3 @@
 transformer_misc Summary:
-AST Parsed     : 119/119 (100.00%)
-Positive Passed: 119/119 (100.00%)
+AST Parsed     : 120/120 (100.00%)
+Positive Passed: 120/120 (100.00%)