Update width heuristic configuration (#4063)

Author: calebcartwright

Configurations.md

@@ -17,6 +17,29 @@ To enable unstable options, set `unstable_features = true` in `rustfmt.toml` or
 
 Below you find a detailed visual guide on all the supported configuration options of rustfmt:
 
+## `array_width` 
+
+Maximum width of an array literal before falling back to vertical formatting.
+
+- **Default value**: `60`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `array_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
+
+## `attr_fn_like_width` 
+
+Maximum width of the args of a function-like attributes before falling back to vertical formatting.
+
+- **Default value**: `70`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `attr_fn_like_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
 
 ## `binop_separator`
 
@@ -272,6 +295,17 @@ where
 }
 ```
 
+## `chain_width` 
+
+Maximum width of a chain to fit on one line.
+
+- **Default value**: `60`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `chain_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
 
 ## `color`
 
@@ -717,6 +751,17 @@ trait Lorem {
 }
 ```
 
+## `fn_call_width` 
+
+Maximum width of the args of a function call before falling back to vertical formatting.
+
+- **Default value**: `60`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `fn_call_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
 
 ## `fn_single_line`
 
@@ -1881,6 +1926,18 @@ specific version of rustfmt is used in your CI, use this option.
 - **Possible values**: any published version (e.g. `"0.3.8"`)
 - **Stable**: No (tracking issue: [#3386](https://github.com/rust-lang/rustfmt/issues/3386))
 
+## `single_line_if_else_max_width` 
+
+Maximum line length for single line if-else expressions. A value of `0` (zero) results in if-else expressions always being broken into multiple lines. Note this occurs when `width_heuristics` is set to `Off`.
+
+- **Default value**: `50`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `single_line_if_else_max_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
+
 ## `space_after_colon`
 
 Leave a space after the colon.
@@ -2080,6 +2137,29 @@ fn main() {
 
 See also: [`indent_style`](#indent_style).
 
+## `struct_lit_width` 
+
+Maximum width in the body of a struct literal before falling back to vertical formatting. A value of `0` (zero) results in struct literals always being broken into multiple lines. Note this occurs when `width_heuristics` is set to `Off`.
+
+- **Default value**: `18`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `struct_lit_width` will take precedence. 
+
+See also [`max_width`](#max_width), [`width_heuristics`](#width_heuristics), and [`struct_lit_single_line`](#struct_lit_single_line)
+
+## `struct_variant_width` 
+
+Maximum width in the body of a struct variant before falling back to vertical formatting. A value of `0` (zero) results in struct literals always being broken into multiple lines. Note this occurs when `width_heuristics` is set to `Off`.
+
+- **Default value**: `35`
+- **Possible values**: any positive integer that is less than or equal to the value specified for [`max_width`](#max_width)
+- **Stable**: Yes
+
+By default this option is set as a percentage of [`max_width`](#max_width) provided by [`width_heuristics`](#width_heuristics), but a value set directly for `struct_variant_width` will take precedence. 
+
+See also [`max_width`](#max_width) and [`width_heuristics`](#width_heuristics)
 
 ## `tab_spaces`
 
@@ -2270,15 +2350,45 @@ fn main() {
 }
 ```
 
-## `use_small_heuristics`
+## `width_heuristics`
+
+This option can be used to simplify the management and bulk updates of the granular width configuration settings ([`fn_call_width`](#fn_call_width), [`attr_fn_like_width`](#attr_fn_like_width), [`struct_lit_width`](#struct_lit_width), [`struct_variant_width`](#struct_variant_width), [`array_width`](#array_width), [`chain_width`](#chain_width), [`single_line_if_else_max_width`](#single_line_if_else_max_width)), that respectively control when formatted constructs are multi-lined/vertical based on width.
 
-Whether to use different formatting for items and expressions if they satisfy a heuristic notion of 'small'.
+Note that explicitly provided values for the width configuration settings take precedence and override the calculated values determined by `width_heuristics`. 
 
-- **Default value**: `"Default"`
-- **Possible values**: `"Default"`, `"Off"`, `"Max"`
+- **Default value**: `"Scaled"`
+- **Possible values**: `"Scaled"`, `"Off"`, `"Max"`
 - **Stable**: Yes
 
-#### `Default` (default):
+#### `Scaled` (default):
+When `width_heuristics` is set to `Scaled`, the values for the granular width settings are calculated as a ratio of the value for `max_width`.
+
+The ratios are:
+* [`fn_call_width`](#fn_call_width) - `60%`
+* [`attr_fn_like_width`](#attr_fn_like_width) - `70%`
+* [`struct_lit_width`](#struct_lit_width) - `18%`
+* [`struct_variant_width`](#struct_variant_width) - `35%`
+* [`array_width`](#array_width) - `60%`
+* [`chain_width`](#chain_width) - `60%`
+* [`single_line_if_else_max_width`](#single_line_if_else_max_width) - `50%`
+
+For example when `max_width` is set to `100`, the width settings are:
+* `fn_call_width=60`
+* `attr_fn_like_width=70`
+* `struct_lit_width=18`
+* `struct_variant_width=35`
+* `array_width=60`
+* `chain_width=60`
+* `single_line_if_else_max_width=50`
+
+and when `max_width` is set to `200`:
+* `fn_call_width=120`
+* `attr_fn_like_width=140`
+* `struct_lit_width=36`
+* `struct_variant_width=70`
+* `array_width=120`
+* `chain_width=120`
+* `single_line_if_else_max_width=100`
 
 ```rust
 enum Lorem {
@@ -2309,6 +2419,7 @@ fn main() {
 ```
 
 #### `Off`:
+When `width_heuristics` is set to `Off`, the granular width settings are functionally disabled and ignored. See the documentation for the respective width config options for specifics. 
 
 ```rust
 enum Lorem {
@@ -2337,6 +2448,16 @@ fn main() {
 ```
 
 #### `Max`:
+When `width_heuristics` is set to `Max`, then each granular width setting is set to the same value as `max_width`.
+
+So if `max_width` is set to `200`, then all the width settings are also set to `200`.
+* `fn_call_width=200`
+* `attr_fn_like_width=200`
+* `struct_lit_width=200`
+* `struct_variant_width=200`
+* `array_width=200`
+* `chain_width=200`
+* `single_line_if_else_max_width=200`
 
 ```rust
 enum Lorem {
@@ -2354,6 +2475,17 @@ fn main() {
 }
 ```
 
+
+See also:
+* [`max_width`](#max_width)
+* [`fn_call_width`](#fn_call_width)
+* [`attr_fn_like_width`](#attr_fn_like_width)
+* [`struct_lit_width`](#struct_lit_width)
+* [`struct_variant_width`](#struct_variant_width)
+* [`array_width`](#array_width)
+* [`chain_width`](#chain_width)
+* [`single_line_if_else_max_width`](#single_line_if_else_max_width)
+
 ## `use_try_shorthand`
 
 Replace uses of the try! macro by the ? shorthand

rustfmt-core/rustfmt-config/src/config_type.rs

@@ -96,7 +96,15 @@ macro_rules! create_config {
                     (self.0).$i.1 = true;
                     (self.0).$i.2 = value;
                     match stringify!($i) {
-                        "max_width" | "use_small_heuristics" => self.0.set_heuristics(),
+                        "max_width"
+                        | "width_heuristics"
+                        | "fn_call_width"
+                        | "single_line_if_else_max_width"
+                        | "attr_fn_like_width"
+                        | "struct_lit_width"
+                        | "struct_variant_width"
+                        | "array_width"
+                        | "chain_width" => self.0.set_heuristics(),
                         "license_template_path" => self.0.set_license_template(),
                         &_ => (),
                     }
@@ -228,16 +236,24 @@ macro_rules! create_config {
                 }
 
                 match key {
-                    "max_width" | "use_small_heuristics" => self.set_heuristics(),
+                    "max_width"
+                    | "width_heuristics"
+                    | "fn_call_width"
+                    | "single_line_if_else_max_width"
+                    | "attr_fn_like_width"
+                    | "struct_lit_width"
+                    | "struct_variant_width"
+                    | "array_width"
+                    | "chain_width" => self.set_heuristics(),
                     "license_template_path" => self.set_license_template(),
                     &_ => (),
                 }
             }
 
             #[allow(unreachable_pub)]
             pub fn is_hidden_option(name: &str) -> bool {
-                const HIDE_OPTIONS: [&str; 6] = [
-                    "verbose", "verbose_diff", "file_lines", "width_heuristics",
+                const HIDE_OPTIONS: [&str; 5] = [
+                    "verbose", "verbose_diff", "file_lines",
                     "recursive", "print_misformatted_file_names",
                 ];
                 HIDE_OPTIONS.contains(&name)
@@ -280,16 +296,93 @@ macro_rules! create_config {
                 )+
             }
 
+            fn set_width_heuristics(&mut self, heuristics: WidthHeuristics) {
+                let max_width = self.max_width.2;
+                let get_width_value = |
+                    was_set: bool,
+                    override_value: usize,
+                    heuristic_value: usize,
+                    config_key: &str,
+                | -> usize {
+                    if !was_set {
+                        return heuristic_value;
+                    }
+                    if override_value > max_width {
+                        eprintln!(
+                            "`{0}` cannot have a value that exceeds `max_width`. \
+                            `{0}` will be set to the same value as `max_width`",
+                            config_key,
+                        );
+                        return max_width;
+                    }
+                    override_value
+                };
+
+                let fn_call_width = get_width_value(
+                    self.was_set().fn_call_width(),
+                    self.fn_call_width.2,
+                    heuristics.fn_call_width,
+                    "fn_call_width",
+                );
+                self.fn_call_width.2 = fn_call_width;
+
+                let attr_fn_like_width = get_width_value(
+                    self.was_set().attr_fn_like_width(),
+                    self.attr_fn_like_width.2,
+                    heuristics.attr_fn_like_width,
+                    "attr_fn_like_width",
+                );
+                self.attr_fn_like_width.2 = attr_fn_like_width;
+
+                let struct_lit_width = get_width_value(
+                    self.was_set().struct_lit_width(),
+                    self.struct_lit_width.2,
+                    heuristics.struct_lit_width,
+                    "struct_lit_width",
+                );
+                self.struct_lit_width.2 = struct_lit_width;
+
+                let struct_variant_width = get_width_value(
+                    self.was_set().struct_variant_width(),
+                    self.struct_variant_width.2,
+                    heuristics.struct_variant_width,
+                    "struct_variant_width",
+                );
+                self.struct_variant_width.2 = struct_variant_width;
+
+                let array_width = get_width_value(
+                    self.was_set().array_width(),
+                    self.array_width.2,
+                    heuristics.array_width,
+                    "array_width",
+                );
+                self.array_width.2 = array_width;
+
+                let chain_width = get_width_value(
+                    self.was_set().chain_width(),
+                    self.chain_width.2,
+                    heuristics.chain_width,
+                    "chain_width",
+                );
+                self.chain_width.2 = chain_width;
+
+                let single_line_if_else_max_width = get_width_value(
+                    self.was_set().single_line_if_else_max_width(),
+                    self.single_line_if_else_max_width.2,
+                    heuristics.single_line_if_else_max_width,
+                    "single_line_if_else_max_width",
+                );
+                self.single_line_if_else_max_width.2 = single_line_if_else_max_width;
+            }
+
             fn set_heuristics(&mut self) {
-                if self.use_small_heuristics.2 == Heuristics::Default {
-                    let max_width = self.max_width.2;
-                    self.set().width_heuristics(WidthHeuristics::scaled(max_width));
-                } else if self.use_small_heuristics.2 == Heuristics::Max {
-                    let max_width = self.max_width.2;
-                    self.set().width_heuristics(WidthHeuristics::set(max_width));
-                } else {
-                    self.set().width_heuristics(WidthHeuristics::null());
-                }
+                let max_width = self.max_width.2;
+                match self.width_heuristics.2 {
+                    Heuristics::Scaled =>
+                        self.set_width_heuristics(WidthHeuristics::scaled(max_width)),
+                    Heuristics::Max => self.set_width_heuristics(WidthHeuristics::set(max_width)),
+                    Heuristics::Off => self.set_width_heuristics(WidthHeuristics::null()),
+                };
             }
 
             fn set_license_template(&mut self) {