support formatting half open ranges (#4044)

Author: calebcartwright

rustfmt-core/rustfmt-lib/src/expr.rs

@@ -833,11 +833,8 @@ impl<'a> ControlFlow<'a> {
                 .span_after(self.span, self.connector.trim());
             let comments_span = mk_sp(comments_lo, expr.span.lo());
 
-            let missing_comments = match rewrite_missing_comment(
-                comments_span,
-                cond_shape,
-                context,
-            ) {
+            let missing_comments = match rewrite_missing_comment(comments_span, cond_shape, context)
+            {
                 None => "".to_owned(),
                 Some(comment) if self.connector.is_empty() || comment.is_empty() => comment,
                 // Handle same-line block comments:

rustfmt-core/rustfmt-lib/src/patterns.rs

@@ -55,6 +55,17 @@ fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
     }
 }
 
+struct RangeOperand<'a>(&'a Option<ptr::P<ast::Expr>>);
+
+impl<'a> Rewrite for RangeOperand<'a> {
+    fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
+        match &self.0 {
+            None => Some("".to_owned()),
+            Some(ref exp) => exp.rewrite(context, shape),
+        }
+    }
+}
+
 impl Rewrite for Pat {
     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
         match self.kind {
@@ -179,29 +190,34 @@ impl Rewrite for Pat {
                     None
                 }
             }
-            PatKind::Range(ref lhs, ref rhs, ref end_kind) => match (lhs, rhs) {
-                (Some(lhs), Some(rhs)) => {
-                    let infix = match end_kind.node {
-                        RangeEnd::Included(RangeSyntax::DotDotDot) => "...",
-                        RangeEnd::Included(RangeSyntax::DotDotEq) => "..=",
-                        RangeEnd::Excluded => "..",
+            PatKind::Range(ref lhs, ref rhs, ref end_kind) => {
+                let infix = match end_kind.node {
+                    RangeEnd::Included(RangeSyntax::DotDotDot) => "...",
+                    RangeEnd::Included(RangeSyntax::DotDotEq) => "..=",
+                    RangeEnd::Excluded => "..",
+                };
+                let infix = if context.config.spaces_around_ranges() {
+                    let lhs_spacing = match lhs {
+                        None => "",
+                        Some(_) => " ",
                     };
-                    let infix = if context.config.spaces_around_ranges() {
-                        format!(" {} ", infix)
-                    } else {
-                        infix.to_owned()
+                    let rhs_spacing = match rhs {
+                        None => "",
+                        Some(_) => " ",
                     };
-                    rewrite_pair(
-                        &**lhs,
-                        &**rhs,
-                        PairParts::infix(&infix),
-                        context,
-                        shape,
-                        SeparatorPlace::Front,
-                    )
-                }
-                (_, _) => unimplemented!(),
-            },
+                    format!("{}{}{}", lhs_spacing, infix, rhs_spacing)
+                } else {
+                    infix.to_owned()
+                };
+                rewrite_pair(
+                    &RangeOperand(lhs),
+                    &RangeOperand(rhs),
+                    PairParts::infix(&infix),
+                    context,
+                    shape,
+                    SeparatorPlace::Front,
+                )
+            }
             PatKind::Ref(ref pat, mutability) => {
                 let prefix = format!("&{}", format_mutability(mutability));
                 rewrite_unary_prefix(context, &prefix, &**pat, shape)

rustfmt-core/rustfmt-lib/tests/source/configs/spaces_around_ranges/false.rs

@@ -20,3 +20,15 @@ fn main() {
         _ => bar,
     }
 }
+
+fn half_open() {
+    match [5 .. 4, 99 .. 105, 43 .. 44] {
+        [_, 99 .., _] => {}
+        [_, .. 105, _] => {}
+        _ => {}
+    };
+
+    if let ..=   5 = 0 {}
+    if let .. 5 = 0 {}
+    if let 5 .. = 0 {}
+}

rustfmt-core/rustfmt-lib/tests/source/configs/spaces_around_ranges/true.rs

@@ -20,3 +20,15 @@ fn main() {
         _ => bar,
     }
 }
+
+fn half_open() {
+    match [5..4, 99..105, 43..44] {
+        [_, 99.., _] => {}
+        [_, ..105, _] => {}
+        _ => {}
+    };
+
+    if let ..=5 = 0 {}
+    if let ..5 = 0 {}
+    if let 5.. = 0 {}
+}

rustfmt-core/rustfmt-lib/tests/target/configs/spaces_around_ranges/false.rs

@@ -20,3 +20,15 @@ fn main() {
         _ => bar,
     }
 }
+
+fn half_open() {
+    match [5..4, 99..105, 43..44] {
+        [_, 99.., _] => {}
+        [_, ..105, _] => {}
+        _ => {}
+    };
+
+    if let ..=5 = 0 {}
+    if let ..5 = 0 {}
+    if let 5.. = 0 {}
+}

rustfmt-core/rustfmt-lib/tests/target/configs/spaces_around_ranges/true.rs

@@ -20,3 +20,15 @@ fn main() {
         _ => bar,
     }
 }
+
+fn half_open() {
+    match [5 .. 4, 99 .. 105, 43 .. 44] {
+        [_, 99 .., _] => {}
+        [_, .. 105, _] => {}
+        _ => {}
+    };
+
+    if let ..= 5 = 0 {}
+    if let .. 5 = 0 {}
+    if let 5 .. = 0 {}
+}