Fix exponential syntax (rescript-lang#7174)

* Check for digits after exponent char * Add tests * Update CHANGELOG * Better variable name * Update CHANGELOG

Author: shulhi

CHANGELOG.md

@@ -11,6 +11,7 @@
 > - :nail_care: [Polish]
 
 # 12.0.0-alpha.6 (Unreleased)
+- Fix exponential notation syntax. https://github.com/rescript-lang/rescript/pull/7174
 
 # 12.0.0-alpha.5
 

compiler/syntax/src/res_scanner.ml

@@ -209,24 +209,30 @@ let scan_identifier scanner =
 
 let scan_digits scanner ~base =
  if base <= 10 then
- let rec loop scanner =
+ let rec loop scanner found_digits =
  match scanner.ch with
- | '0' .. '9' | '_' ->
+ | '0' .. '9' ->
  next scanner;
- loop scanner
- | _ -> ()
+ loop scanner true
+ | '_' ->
+ next scanner;
+ loop scanner false
+ | _ -> found_digits
  in
- loop scanner
+ loop scanner false
  else
- let rec loop scanner =
+ let rec loop scanner found_digits =
  match scanner.ch with
  (* hex *)
- | '0' .. '9' | 'a' .. 'f' | 'A' .. 'F' | '_' ->
+ | '0' .. '9' | 'a' .. 'f' | 'A' .. 'F' ->
+ next scanner;
+ loop scanner true
+ | '_' ->
  next scanner;
- loop scanner
- | _ -> ()
+ loop scanner false
+ | _ -> found_digits
  in
- loop scanner
+ loop scanner false
 
 (* float: (0…9) { 0…9∣ _ } [. { 0…9∣ _ }] [(e∣ E) [+∣ -] (0…9) { 0…9∣ _ }] *)
 let scan_number scanner =
@@ -251,25 +257,30 @@ let scan_number scanner =
  8)
  | _ -> 10
  in
- scan_digits scanner ~base;
+ ignore (scan_digits scanner ~base);
 
  (* *)
  let is_float =
  if '.' == scanner.ch then (
  next scanner;
- scan_digits scanner ~base;
+ ignore (scan_digits scanner ~base);
  true)
  else false
  in
 
  (* exponent part *)
  let is_float =
+ let start_pos = position scanner in
  match scanner.ch with
  | 'e' | 'E' | 'p' | 'P' ->
  (match peek scanner with
  | '+' | '-' -> next2 scanner
  | _ -> next scanner);
- scan_digits scanner ~base;
+ let end_pos = position scanner in
+ let found_digits = scan_digits scanner ~base in
+ if not found_digits then
+ scanner.err ~start_pos ~end_pos
+ (Diagnostics.message "Expected digits after exponential notation.");
  true
  | _ -> is_float
  in

tests/syntax_tests/data/parsing/errors/scanner/expected/exponent_notation.res.txt

@@ -0,0 +1,30 @@
+
+ Syntax error!
+ syntax_tests/data/parsing/errors/scanner/exponent_notation.res:7:10
+
+ 5 │ let x = 1_e_1
+ 6 │ 
+ 7 │ let x = 1e
+ 8 │ 
+ 9 │ let x = 1_e_
+
+ Expected digits after exponential notation.
+
+
+ Syntax error!
+ syntax_tests/data/parsing/errors/scanner/exponent_notation.res:9:11
+
+ 7 │ let x = 1e
+ 8 │ 
+ 9 │ let x = 1_e_
+ 10 │ 
+ 11 │ let x = 1.
+
+ Expected digits after exponential notation.
+
+let x = 1e1
+let x = 1e_1
+let x = 1_e_1
+let x = 1e
+let x = 1_e_
+let x = 1.

tests/syntax_tests/data/parsing/errors/scanner/exponent_notation.res

@@ -0,0 +1,11 @@
+let x = 1e1
+
+let x = 1e_1
+
+let x = 1_e_1
+
+let x = 1e
+
+let x = 1_e_
+
+let x = 1.