Add test for width heuristics

src/config/config_type.rs

@@ -130,7 +130,7 @@ macro_rules! create_config {
             pub fn $i(&mut self, value: $ty) {
                 (self.0).$i.2 = value;
                 match stringify!($i) {
-                    "use_small_heuristics" => self.0.set_heuristics(),
+                    "max_width" | "use_small_heuristics" => self.0.set_heuristics(),
                     "license_template_path" => self.0.set_license_template(),
                     &_ => (),
                 }
@@ -292,7 +292,7 @@ macro_rules! create_config {
                 }
 
                 match key {
-                    "use_small_heuristics" => self.set_heuristics(),
+                    "max_width" | "use_small_heuristics" => self.set_heuristics(),
                     "license_template_path" => self.set_license_template(),
                     &_ => (),
                 }

tests/source/width-heuristics.rs

@@ -0,0 +1,28 @@
+// rustfmt-max_width: 120
+
+// elems on multiple lines for max_width 100, but same line for max_width 120
+fn foo(e: Enum) {
+    match e {
+        Enum::Var {
+            elem1,
+            elem2,
+            elem3,
+        } => {
+            return;
+        }
+    }
+}
+
+// elems not on same line for either max_width 100 or 120
+fn bar(e: Enum) {
+    match e {
+        Enum::Var {
+            elem1,
+            elem2,
+            elem3,
+            elem4,
+        } => {
+            return;
+        }
+    }
+}

tests/target/width-heuristics.rs

@@ -0,0 +1,24 @@
+// rustfmt-max_width: 120
+
+// elems on multiple lines for max_width 100, but same line for max_width 120
+fn foo(e: Enum) {
+    match e {
+        Enum::Var { elem1, elem2, elem3 } => {
+            return;
+        }
+    }
+}
+
+// elems not on same line for either max_width 100 or 120
+fn bar(e: Enum) {
+    match e {
+        Enum::Var {
+            elem1,
+            elem2,
+            elem3,
+            elem4,
+        } => {
+            return;
+        }
+    }
+}