fix(parse): do not begin terse function expression with requires

Author: JohelEGP

regression-tests/pure2-requires-clauses.cpp2

@@ -17,6 +17,9 @@ f:  <T: type, U: type>
 
 v: <T> const T requires std::same_as<T, i32> = 0;
 
+g: <T> () requires true = { }
+g: () (requires { _ = 0; });
+
 main: () = {
     x: X<int,int> = ();
     std::cout << f<int,int>(2,5);

regression-tests/test-results/pure2-requires-clauses.cpp

@@ -42,6 +42,12 @@ CPP2_REQUIRES_ (std::same_as<T,cpp2::i32>)
 #line 18 "pure2-requires-clauses.cpp2"
 extern T const v;
 
+template<typename T> auto g() -> void
+CPP2_REQUIRES (true)
+#line 20 "pure2-requires-clauses.cpp2"
+;
+[[nodiscard]] auto g() -> auto;
+
 auto main() -> int;
 
 
@@ -66,6 +72,12 @@ requires (std::same_as<T,cpp2::i32>)
 #line 18 "pure2-requires-clauses.cpp2"
 T const v {0}; 
 
+template<typename T> auto g() -> void
+requires (true)
+#line 20 "pure2-requires-clauses.cpp2"
+{}
+[[nodiscard]] auto g() -> auto { return requires {0; 
+}; }
 auto main() -> int{
     X<int,int> x {}; 
     std::cout << f<int,int>(2, 5);

source/parse.h

@@ -7816,7 +7816,9 @@ class parser
         if (curr().type() != lexeme::Arrow)
         {
             auto start_pos = pos;
-            auto at_an_expression_statement = expression_statement(true) != nullptr;
+            auto at_an_expression_statement =
+                curr() != "requires"
+                && expression_statement(true) != nullptr;
             pos = start_pos;    // backtrack no matter what, we're just peeking here
 
             if (at_an_expression_statement) {