Format heterogeneous try blocks

Author: ia0

src/expr.rs

@@ -385,8 +385,33 @@ pub(crate) fn format_expr(
                 ))
             }
         }
-        // FIXME: heterogeneous try blocks, which include a type so are harder to format
-        ast::ExprKind::TryBlock(_, Some(_)) => Err(RewriteError::Unknown),
+        ast::ExprKind::TryBlock(ref block, Some(ref ty)) => {
+            let keyword = "try bikeshed ";
+            // 2 = " {".len()
+            let ty_shape = shape
+                .shrink_left(keyword.len())
+                .and_then(|shape| shape.sub_width(2))
+                .max_width_error(shape.width, expr.span)?;
+            let ty_str = ty.rewrite_result(context, ty_shape)?;
+            let prefix = format!("{keyword}{ty_str} ");
+            if let rw @ Ok(_) =
+                rewrite_single_line_block(context, &prefix, block, Some(&expr.attrs), None, shape)
+            {
+                rw
+            } else {
+                let budget = shape.width.saturating_sub(prefix.len());
+                Ok(format!(
+                    "{prefix}{}",
+                    rewrite_block(
+                        block,
+                        Some(&expr.attrs),
+                        None,
+                        context,
+                        Shape::legacy(budget, shape.indent)
+                    )?
+                ))
+            }
+        }
         ast::ExprKind::Gen(capture_by, ref block, ref kind, _) => {
             let mover = if matches!(capture_by, ast::CaptureBy::Value { .. }) {
                 "move "

tests/source/try_blocks_heterogeneous.rs

@@ -0,0 +1,34 @@
+// rustfmt-edition: 2018
+
+fn main() -> Result<(), !> {
+    let _x = try bikeshed Option<_> {
+        4
+    };
+
+    try bikeshed Result<_, _> {}
+}
+
+fn baz() -> Option<i32> {
+    if (1 == 1) {
+        return try bikeshed Option<i32> {
+            5
+        };
+    }
+
+    // test
+    let x = try bikeshed Option<()> {
+        // try blocks are great
+    };
+
+    let y = try bikeshed Option<i32> {
+        6
+    }; // comment
+
+    let x = try bikeshed Option<i32> { baz()?; baz()?; baz()?; 7 };
+
+    let x = try bikeshed Foo<Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar> { 1 + 1 + 1 };
+
+    let x = try bikeshed Foo<Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar> {};
+
+    return None;
+}

tests/target/try_blocks_heterogeneous.rs

@@ -0,0 +1,36 @@
+// rustfmt-edition: 2018
+
+fn main() -> Result<(), !> {
+    let _x = try bikeshed Option<_> { 4 };
+
+    try bikeshed Result<_, _> {}
+}
+
+fn baz() -> Option<i32> {
+    if (1 == 1) {
+        return try bikeshed Option<i32> { 5 };
+    }
+
+    // test
+    let x = try bikeshed Option<()> {
+        // try blocks are great
+    };
+
+    let y = try bikeshed Option<i32> { 6 }; // comment
+
+    let x = try bikeshed Option<i32> {
+        baz()?;
+        baz()?;
+        baz()?;
+        7
+    };
+
+    let x = try bikeshed Foo<Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar> {
+        1 + 1 + 1
+    };
+
+    let x =
+        try bikeshed Foo<Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar, Bar> {};
+
+    return None;
+}