Digit separator doesn't parse with opening brace

Fixes hsutter#862.

Author: ntrel

regression-tests/pure2-numeric-literal.cpp2

@@ -0,0 +1,8 @@
+// } on same line
+niam: () = { _ = 0'1; }
+
+main: () = {
+    x := 0'1; // OK
+    if 1 { x = 1'2; } // same
+    assert(x == 12);
+}

regression-tests/test-results/pure2-numeric-literal.cpp

@@ -0,0 +1,32 @@
+
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-numeric-literal.cpp2"
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-numeric-literal.cpp2"
+// } on same line
+#line 2 "pure2-numeric-literal.cpp2"
+auto niam() -> void;
+
+auto main() -> int;
+
+//=== Cpp2 function definitions =================================================
+
+#line 1 "pure2-numeric-literal.cpp2"
+
+#line 2 "pure2-numeric-literal.cpp2"
+auto niam() -> void{static_cast<void>(0'1); }
+
+auto main() -> int{
+    auto x {0'1}; // OK
+    if (1) {x = 1'2; }// same
+    cpp2::Default.expects(std::move(x) == 12, "");
+}
+

source/io.h

@@ -719,6 +719,7 @@ auto process_cpp2_line(
     auto prev2 = ' ';
     auto in_string_literal = false;
     auto in_char_literal   = false;
+    auto in_numeric_literal = false;
 
     for (auto i = colno_t{0}; i < ssize(line); ++i)
     {
@@ -782,10 +783,22 @@ auto process_cpp2_line(
                 if (prev != '\\' || prev2 == '\\') { in_string_literal = true; }
 
             break;case '\'':
-                if (prev != '\\' || prev2 == '\\') { in_char_literal = true; }
+                if (!in_numeric_literal && (prev != '\\' || prev2 == '\\'))
+                {
+                    in_char_literal = true;
+                }
 
             break;default: ;
             }
+            if (in_numeric_literal)
+            {
+                // Note: this allows _ but that will be caught elsewhere
+                if (!is_identifier_continue(line[i]) && line[i] != '\'')
+                    in_numeric_literal = false;
+            }
+            // either decimal or other numeric literal starting with 0
+            else if (line[i] >= '0' && line[i] <= '9')
+                in_numeric_literal = true;
         }
 
         prev2 = prev;