Change use_small_heuristics to an enum and stabilise

Since it is now an enum, we can be future compatible since we can add variants
for different heuristics.

Closes #1974

Author: nrc

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## [Unreleased]
 
+- `use_small_heuristics` changed to be an enum and stabilised. Configuration
+  options are now ready for 1.0.
+
 ## [0.4.1] 2018-03-16
 
 ### Added

Configurations.md

@@ -275,11 +275,11 @@ fn lorem<Ipsum, Dolor, Sit, Amet>() -> T
 
 Whether to use different formatting for items and expressions if they satisfy a heuristic notion of 'small'.
 
-- **Default value**: `true`
-- **Possible values**: `true`, `false`
-- **Stable**: No
+- **Default value**: `Default`
+- **Possible values**: `Default`, `Off`
+- **Stable**: Yess
 
-#### `true` (default):
+#### `Default` (default):
 
 ```rust
 enum Lorem {
@@ -309,7 +309,7 @@ fn main() {
 }
 ```
 
-#### `false`:
+#### `Off`:
 
 ```rust
 enum Lorem {

src/config/config_type.rs

@@ -399,7 +399,7 @@ macro_rules! create_config {
             }
 
             fn set_heuristics(&mut self) {
-                if self.use_small_heuristics.2 {
+                if self.use_small_heuristics.2 == Heuristics::Default {
                     let max_width = self.max_width.2;
                     self.set().width_heuristics(WidthHeuristics::scaled(max_width));
                 } else {

src/config/mod.rs

@@ -41,8 +41,8 @@ create_config! {
     hard_tabs: bool, false, true, "Use tab characters for indentation, spaces for alignment";
     tab_spaces: usize, 4, true, "Number of spaces per tab";
     newline_style: NewlineStyle, NewlineStyle::Unix, true, "Unix or Windows line endings";
-    use_small_heuristics: bool, true, false, "Whether to use different formatting for items and \
-        expressions if they satisfy a heuristic notion of 'small'.";
+    use_small_heuristics: Heuristics, Heuristics::Default, true, "Whether to use different \
+        formatting for items and expressions if they satisfy a heuristic notion of 'small'.";
     indent_style: IndentStyle, IndentStyle::Block, false, "How do we indent expressions or items.";
 
     // Comments and strings
@@ -236,7 +236,7 @@ mod test {
         create_config! {
             // Options that are used by the generated functions
             max_width: usize, 100, true, "Maximum width of each line";
-            use_small_heuristics: bool, true, false,
+            use_small_heuristics: Heuristics, Heuristics::Default, true,
                 "Whether to use different formatting for items and \
                  expressions if they satisfy a heuristic notion of 'small'.";
             license_template_path: String, String::default(), false,

src/config/options.rs

@@ -151,6 +151,13 @@ configuration_option_enum! { TypeDensity:
     Wide,
 }
 
+configuration_option_enum! { Heuristics:
+    // Turn off any heuristics
+    Off,
+    // Use Rustfmt's defaults
+    Default,
+}
+
 impl Density {
     pub fn to_list_tactic(self) -> ListTactic {
         match self {

tests/source/chains.rs

@@ -1,5 +1,5 @@
 // rustfmt-normalize_comments: true
-// rustfmt-use_small_heuristics: false
+// rustfmt-use_small_heuristics: Off
 // Test chain formatting.
 
 fn main() {

tests/target/chains.rs

@@ -1,5 +1,5 @@
 // rustfmt-normalize_comments: true
-// rustfmt-use_small_heuristics: false
+// rustfmt-use_small_heuristics: Off
 // Test chain formatting.
 
 fn main() {