Rustfmt: Incorrect indent of closure inside struct

[nrc]

See https://pbs.twimg.com/media/C5UtJRrXUAAQBIp.jpg:large

[jonhoo]

Much smaller example:

struct Foo;
impl Foo {
    fn foo(&self) -> Box<FnMut(i64) -> i64> {
        Box::new(move |aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa| {
            aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
        })
    }
}

@@ -2,7 +2,7 @@
 impl Foo {
     fn foo(&self) -> Box<FnMut(i64) -> i64> {
         Box::new(move |aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa| {
-            aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-        })
+                     aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+                 })
     }
 }

[jonhoo]

This seems to be happening to me all over the place in my code. It looks like it's now standard to align the body of a closure at one indent deeper than the first | of the closure prologue, rather than one more than the current alignment. This causes a lot of code to end up being very deeply aligned (as above), and looks quite strange. Here is another diff to illustrate:

         let getters: Vec<_> = getters.into_iter()
             .enumerate()
             .map(|(i, g)| {
-                thread::Builder::new()
-                    .name(format!("GET{}", i))
-                    .spawn(move || exercise::launch_reader(g, config))
-                    .unwrap()
-            })
+                     thread::Builder::new()
+                         .name(format!("GET{}", i))
+                         .spawn(move || exercise::launch_reader(g, config))
+                         .unwrap()
+                 })
             .collect();

However, it doesn't seem to happen everywhere:

         Some(self.domain_dependencies
-            .iter()
-            .map(|(d, v)| {
-                let earliest: i64 = v.iter()
-                    .filter_map(|b| self.toplevel.get(b))
-                    .chain(self.last_migration.iter())
-                    .max()
-                    .cloned()
-                    .unwrap_or(0);
-                (*d, earliest)
-            })
-            .collect())
+                 .iter()
+                 .map(|(d, v)| {
+            let earliest: i64 = v.iter()
+                .filter_map(|b| self.toplevel.get(b))
+                .chain(self.last_migration.iter())
+                .max()
+                .cloned()
+                .unwrap_or(0);
+            (*d, earliest)
+        })
+                 .collect())

(yes, I know some of this code isn't pretty to begin with, but that's an orthogonal concern)

[nrc]

It looks like it's now standard to align the body of a closure at one indent deeper than the first | of the closure prologue

This is correct (and intentional). It's a more strict interpretation of visual indent rules. We do have a heuristic (7 lines or something, it is configurable) where we break a closure into block indent rather than visual. When we move to block indenting fn args, then this will always happen.

[nrc]

Closing because I think this is actually intended behaviour.

[jonhoo]

@nrc Even the second example in the last comment? That doesn't seem to behave that way?

This visual style is significantly more jarring to me than the old one, and causes some pretty serious indentation anywhere you do, say, Box::new(move || {. Is there a way to override this behavior to instead always switch to a block indent?

[nrc]

Even the second example in the last comment?

That example seems to be hitting the threshold where we block indent.

Is there a way to override this behavior to instead always switch to a block indent?

I'm working on it! I expect to land this in the next two weeks.

[jonhoo]

Where is the recommendation for using visual indent so aggressively? I don't see it in the fmt-rfcs example, nor in the guide?

It also keeps producing really weird results for me, especially when pushing against the line length limit, as @nical pointed out in https://github.com/rust-lang-nursery/fmt-rfcs/issues/8#issuecomment-262916202. For example:

                        m.map_data(|mut rs| {
                            rs.retain(|r| {
                                r.iter().enumerate().all(|(i, v)| {
                                    if let Some(ref rv) = on[i] {
                                        rv == v
                                    } else {
                                        true
                                    }
                                })
                            });
                            rs
                        });

becomes

                        m.map_data(|mut rs| {
                            rs.retain(|r| {
                                          r.iter().enumerate().all(|(i, v)| if let Some(ref rv) =
                                    on[i] {
                                                                       rv == v
                                                                   } else {
                                                                       true
                                                                   })
                                      });
                            rs
                        });

[nrc]

Where is the recommendation for using visual indent so aggressively?

It's a consequence of some internal reorganisation. It's actually in the service of moving to block indent in more places, but is temporarily having the opposite effect.