Add spaces_within_square_brackets config option. (#1191)

* Add spaces_within_square_brackets config option.

Enabling the config enforces spaces within various array/slice brackets.

* Fixed budget-calculations for [] spacing

src/config.rs

@@ -417,6 +417,7 @@ create_config! {
         "Leave a space after the colon in a trait or lifetime bound";
     spaces_around_ranges: bool, false, "Put spaces around the  .. and ... range operators";
     spaces_within_angle_brackets: bool, false, "Put spaces within non-empty generic arguments";
+    spaces_within_square_brackets: bool, false, "Put spaces within non-empty square brackets";
     spaces_within_parens: bool, false, "Put spaces within non-empty parentheses";
     use_try_shorthand: bool, false, "Replace uses of the try! macro by the ? shorthand";
     write_mode: WriteMode, WriteMode::Replace,

src/expr.rs

@@ -206,10 +206,16 @@ fn format_expr(expr: &ast::Expr,
             rewrite_pair(&**expr, &**ty, "", ": ", "", context, width, offset)
         }
         ast::ExprKind::Index(ref expr, ref index) => {
-            rewrite_pair(&**expr, &**index, "", "[", "]", context, width, offset)
+            let use_spaces = context.config.spaces_within_square_brackets;
+            let lbr = if use_spaces { "[ " } else { "[" };
+            let rbr = if use_spaces { " ]" } else { "]" };
+            rewrite_pair(&**expr, &**index, "", lbr, rbr, context, width, offset)
         }
         ast::ExprKind::Repeat(ref expr, ref repeats) => {
-            rewrite_pair(&**expr, &**repeats, "[", "; ", "]", context, width, offset)
+            let use_spaces = context.config.spaces_within_square_brackets;
+            let lbr = if use_spaces { "[ " } else { "[" };
+            let rbr = if use_spaces { " ]" } else { "]" };
+            rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, width, offset)
         }
         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
             let delim = match limits {
@@ -303,11 +309,14 @@ pub fn rewrite_array<'a, I>(expr_iter: I,
                             -> Option<String>
     where I: Iterator<Item = &'a ast::Expr>
 {
-    // 1 = [
-    let offset = offset + 1;
+    let bracket_size = if context.config.spaces_within_square_brackets {
+        2  // "[ "
+    } else {
+        1  // "["
+    };
+    let offset = offset + bracket_size;
     let inner_context = &RewriteContext { block_indent: offset, ..*context };
-    // 2 for brackets
-    let max_item_width = try_opt!(width.checked_sub(2));
+    let max_item_width = try_opt!(width.checked_sub(bracket_size * 2));
     let items = itemize_list(context.codemap,
                              expr_iter,
                              "]",
@@ -339,7 +348,11 @@ pub fn rewrite_array<'a, I>(expr_iter: I,
     };
     let list_str = try_opt!(write_list(&items, &fmt));
 
-    Some(format!("[{}]", list_str))
+    Some(if context.config.spaces_within_square_brackets && list_str.len() > 0 {
+        format!("[ {} ]", list_str)
+    } else {
+        format!("[{}]", list_str)
+    })
 }
 
 // This functions is pretty messy because of the rules around closures and blocks:

src/patterns.rs

@@ -94,7 +94,11 @@ impl Rewrite for Pat {
                 let pats = try_opt!(pats);
 
                 // Unwrap all the sub-strings and join them with commas.
-                let result = format!("[{}]", pats.join(", "));
+                let result = if context.config.spaces_within_square_brackets {
+                    format!("[ {} ]", pats.join(", "))
+                } else {
+                    format!("[{}]", pats.join(", "))
+                };
                 wrap_str(result, context.config.max_width, width, offset)
             }
             PatKind::Struct(ref path, ref fields, elipses) => {

src/types.rs

@@ -607,8 +607,17 @@ impl Rewrite for ast::Ty {
                     })
             }
             ast::TyKind::Vec(ref ty) => {
-                let budget = try_opt!(width.checked_sub(2));
-                ty.rewrite(context, budget, offset + 1).map(|ty_str| format!("[{}]", ty_str))
+                let budget = if context.config.spaces_within_square_brackets {
+                    try_opt!(width.checked_sub(4))
+                } else {
+                    try_opt!(width.checked_sub(2))
+                };
+                ty.rewrite(context, budget, offset + 1)
+                    .map(|ty_str| if context.config.spaces_within_square_brackets {
+                        format!("[ {} ]", ty_str)
+                    } else {
+                        format!("[{}]", ty_str)
+                    })
             }
             ast::TyKind::Tup(ref items) => {
                 rewrite_tuple(context,
@@ -622,7 +631,10 @@ impl Rewrite for ast::Ty {
                 rewrite_path(context, false, q_self.as_ref(), path, width, offset)
             }
             ast::TyKind::FixedLengthVec(ref ty, ref repeats) => {
-                rewrite_pair(&**ty, &**repeats, "[", "; ", "]", context, width, offset)
+                let use_spaces = context.config.spaces_within_square_brackets;
+                let lbr = if use_spaces { "[ " } else { "[" };
+                let rbr = if use_spaces { " ]" } else { "]" };
+                rewrite_pair(&**ty, &**repeats, lbr, "; ", rbr, context, width, offset)
             }
             ast::TyKind::Infer => {
                 if width >= 1 {

tests/source/spaces-within-square-brackets.rs

@@ -0,0 +1,28 @@
+// rustfmt-spaces_within_square_brackets: true
+
+fn main() {
+
+    let arr: [i32; 5] = [1, 2, 3, 4, 5];
+    let arr: [i32; 500] = [0; 500];
+
+    let v = vec![1, 2, 3];
+    assert_eq!(arr, [1, 2, 3]);
+
+    let i = arr[0];
+
+    let slice = &arr[1..2];
+
+    let line100_________________________________________________________________________ = [1, 2];
+    let line101__________________________________________________________________________ = [1, 2];
+    let line102___________________________________________________________________________ = [1, 2];
+    let line103____________________________________________________________________________ = [1, 2];
+    let line104_____________________________________________________________________________ = [1, 2];
+
+    let line100_____________________________________________________________________ = vec![1, 2];
+    let line101______________________________________________________________________ = vec![1, 2];
+    let line102_______________________________________________________________________ = vec![1, 2];
+    let line103________________________________________________________________________ = vec![1, 2];
+    let line104_________________________________________________________________________ = vec![1, 2];
+}
+
+fn f(slice: &[i32]) {}

tests/target/spaces-within-square-brackets.rs

@@ -0,0 +1,36 @@
+// rustfmt-spaces_within_square_brackets: true
+
+fn main() {
+
+    let arr: [ i32; 5 ] = [ 1, 2, 3, 4, 5 ];
+    let arr: [ i32; 500 ] = [ 0; 500 ];
+
+    let v = vec![ 1, 2, 3 ];
+    assert_eq!(arr, [ 1, 2, 3 ]);
+
+    let i = arr[ 0 ];
+
+    let slice = &arr[ 1..2 ];
+
+    let line100_________________________________________________________________________ = [ 1, 2 ];
+    let line101__________________________________________________________________________ = [ 1,
+                                                                                              2 ];
+    let line102___________________________________________________________________________ = [ 1,
+                                                                                               2 ];
+    let line103____________________________________________________________________________ = [ 1,
+                                                                                                2 ];
+    let line104_____________________________________________________________________________ =
+        [ 1, 2 ];
+
+    let line100_____________________________________________________________________ = vec![ 1, 2 ];
+    let line101______________________________________________________________________ = vec![ 1,
+                                                                                              2 ];
+    let line102_______________________________________________________________________ = vec![ 1,
+                                                                                               2 ];
+    let line103________________________________________________________________________ = vec![ 1,
+                                                                                                2 ];
+    let line104_________________________________________________________________________ =
+        vec![ 1, 2 ];
+}
+
+fn f(slice: &[ i32 ]) {}