Two different modes:
- Serialize the full Config object. This is useful as
`Config::default().to_toml()` to output a rustfmt.toml with defaults
(#317).
- Serialize only the options that have been accessed. This could be
useful to output a minimal rustfmt.toml for a project. (If the
default value of any unused config item changes, you'll then get the
new default when you come to use it).
This commit doesn't expose this anywhere - deciding a sensible CLI is a
bit trickier.
This commit also has very simple error reporting (Result<String,
String>) - once the CLI is decided, a more sensible method of reporting
errors might become obvious.
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.
Don't make a single line chain when it is was multi line in the source; allow overflow of the last chain element onto the next lines without breaking the chain.
