Merge pull request #2101 from topecongiro/issue-2099

Format match expr with empty body

Author: nrc

src/expr.rs

@@ -1444,15 +1444,10 @@ fn rewrite_match(
     span: Span,
     attrs: &[ast::Attribute],
 ) -> Option<String> {
-    if arms.is_empty() {
-        return None;
-    }
-
     // Do not take the rhs overhead from the upper expressions into account
     // when rewriting match condition.
-    let new_width = context.config.max_width().checked_sub(shape.used_width())?;
     let cond_shape = Shape {
-        width: new_width,
+        width: context.budget(shape.used_width()),
         ..shape
     };
     // 6 = `match `
@@ -1485,9 +1480,12 @@ fn rewrite_match(
     };
 
     let open_brace_pos = if inner_attrs.is_empty() {
-        context
-            .codemap
-            .span_after(mk_sp(cond.span.hi(), arms[0].span().lo()), "{")
+        let hi = if arms.is_empty() {
+            span.hi()
+        } else {
+            arms[0].span().lo()
+        };
+        context.codemap.span_after(mk_sp(cond.span.hi(), hi), "{")
     } else {
         inner_attrs[inner_attrs.len() - 1].span().hi()
     };
@@ -1498,15 +1496,25 @@ fn rewrite_match(
         shape.indent.to_string(context.config)
     };
 
-    Some(format!(
-        "match {}{}{{\n{}{}{}\n{}}}",
-        cond_str,
-        block_sep,
-        inner_attrs_str,
-        arm_indent_str,
-        rewrite_match_arms(context, arms, shape, span, open_brace_pos,)?,
-        shape.indent.to_string(context.config),
-    ))
+    if arms.is_empty() {
+        let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
+        if snippet.trim().is_empty() {
+            Some(format!("match {} {{}}", cond_str))
+        } else {
+            // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
+            Some(context.snippet(span))
+        }
+    } else {
+        Some(format!(
+            "match {}{}{{\n{}{}{}\n{}}}",
+            cond_str,
+            block_sep,
+            inner_attrs_str,
+            arm_indent_str,
+            rewrite_match_arms(context, arms, shape, span, open_brace_pos)?,
+            shape.indent.to_string(context.config),
+        ))
+    }
 }
 
 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {

tests/source/match.rs

@@ -415,3 +415,13 @@ fn match_with_trailing_spaces() {
         None => 1,
     }
 }
+
+fn issue_2099() {
+    let a = match x {
+};
+    let b = match x {
+        
+    };
+
+    match x {}
+}

tests/target/match.rs

@@ -456,3 +456,10 @@ fn match_with_trailing_spaces() {
         None => 1,
     }
 }
+
+fn issue_2099() {
+    let a = match x {};
+    let b = match x {};
+
+    match x {}
+}