[ruby/prism] Report missing end errors at opening token

This commit adds an `expect1_opening` function that expects a token and
attaches the error to the opening token location rather than the current
position. This is useful for errors about missing closing tokens, where
we want to point to the line with the opening token rather than the end
of the file.

For example:

```ruby
def foo
def bar
def baz
       ^ expected an `end` to close the `def` statement
       ^ expected an `end` to close the `def` statement
       ^ expected an `end` to close the `def` statement
```

This would previously produce three identical errors at the end of the
file. After this commit, they would be reported at the opening token
location:

```ruby
def foo
^~~ expected an `end` to close the `def` statement
def bar
^~~ expected an `end` to close the `def` statement
def baz
^~~ expected an `end` to close the `def` statement
```

I considered using the end of the line where the opening token is
located, but in some cases that would be less useful than the opening
token location itself. For example:

```ruby
def foo def bar def baz
```

Here the end of the line where the opening token is located would be the
same for each of the unclosed `def` nodes.

https://github.com/ruby/prism/commit/2d7829f060

0 files changed, 0 insertions, 0 deletions