Fix error messages for unterminated ( and {

If we hit an EOF token, and the character before the EOF is a newline,
we need to rewind the error to the newline so that error messages
contain the correct newline.

Before this commit, we would report an error on the "line of the EOF"
which would come right after the newline

Author: tenderlove

src/prism.c

@@ -476,7 +476,14 @@ pm_parser_err_token(pm_parser_t *parser, const pm_token_t *token, pm_diagnostic_
  * given token and a format string.
  */
 #define PM_PARSER_ERR_TOKEN_FORMAT(parser, token, diag_id, ...) \
-    PM_PARSER_ERR_FORMAT(parser, (token).start, (token).end, diag_id, __VA_ARGS__)
+    do { \
+        pm_token_t errtok = (token); \
+        if (errtok.type == PM_TOKEN_EOF && errtok.start > parser->start && (*(errtok.start - 1) == '\n')) { \
+            PM_PARSER_ERR_FORMAT(parser, errtok.start - 1, (token).end, diag_id, __VA_ARGS__); \
+        } else { \
+            PM_PARSER_ERR_FORMAT(parser, (token).start, (token).end, diag_id, __VA_ARGS__); \
+        } \
+    } while(0)
 
 /**
  * Append an error to the list of errors on the parser using the location of the

test/prism/errors/unterminated_block.txt

@@ -0,0 +1,4 @@
+foo {
+     ^ unexpected end-of-input, assuming it is closing the parent top level context
+     ^ expected a block beginning with `{` to end with `}`
+

test/prism/errors/unterminated_method_parameters.txt

@@ -0,0 +1,3 @@
+foo(
+    ^ unexpected end-of-input; expected a `)` to close the arguments
+

test/prism/errors_test.rb

@@ -32,6 +32,14 @@ class ErrorsTest < TestCase
       end
     end
 
+    def test_newline_preceding_eof
+      err = Prism.parse("foo(").errors.first
+      assert_equal 1, err.location.start_line
+
+      err = Prism.parse("foo(\n").errors.first
+      assert_equal 1, err.location.start_line
+    end
+
     def test_embdoc_ending
       source = <<~RUBY
         =begin\n=end