Switch to accessing config items via method.

Preparation for #865, which proposes adding a flag which outputs which
config options are used during formatting.

This PR should not make any difference to functionality. A lot of this
was search-and-replace.

Some areas worthy of review/discussion:

 - The method for each config item returns a clone of the underlying
   value. We can't simply return an immutable reference, as lots of
   places in the code expect to be able to pass the returned value as
   `bool` (not `&bool). It would be nice if the `bool` items could
   return a copy, but the more complex types a borrowed reference... but
   unfortunately, I couldn't get the macro to do this.
 - A few places (mostly tests and `src/bin/rustfmt.rs`) were overriding
   config items by modifying the fields of the `Config` struct directly.
   They now use the existing `override_value()` method, which has been
   modified to return a `Result` for use by `src/bin/rustfmt.rs`. This
   benefits of this are that the complex `file_lines` and `write_mode`
   strings are now parsed in one place (`Config.override_value`) instead
   of multiple. The disadvantages are that it moves the compile-time
   checks for config names to become run-time checks.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/string.rs b/src/string.rs
index 37a569ce67d..365d205aef1 100644
--- a/src/string.rs
+++ b/src/string.rs
@@ -119,7 +119,7 @@ pub fn rewrite_string<'a>(orig: &str, fmt: &StringFormat<'a>) -> Option<String>
     }
 
     result.push_str(fmt.closer);
-    wrap_str(result, fmt.config.max_width, fmt.shape)
+    wrap_str(result, fmt.config.max_width(), fmt.shape)
 }
 
 #[cfg(test)]