More fine-grained file-lines

[topecongiro]

Currently rustfmt ignores file lines check for items.
Closes #1835.

[nrc]

A couple of minor code-tidiness comments inline

[nrc]

Can we use the context version of skip_span rather than duplicating the code?

[topecongiro]

We could, though we need to call get_context() everytime, which is a bit unfortunate.

[nrc]

We could make this a macro and wouldn't have to repeat the if ... return.

[topecongiro]

Rebased with the change to use macro.

[emilio]

I was super-excited to try this with bindgen, but this causes a bunch of undesired effects.

Current STR (will try to find something more reduced later today):

• Clone https://github.com/rust-lang-nursery/rust-bindgen.
• Apply this diff (for example):

diff --git a/src/lib.rs b/src/lib.rs
index 3a85382..1b68a0a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1268,7 +1268,7 @@ fn filter_builtins(ctx: &BindgenContext, cursor: &clang::Cursor) -> bool {
 
 /// Parse one `Item` from the Clang cursor.
 pub fn parse_one(ctx: &mut BindgenContext,
-                 cursor: clang::Cursor,
+             cursor: clang::Cursor,
                  parent: Option<ItemId>)
                  -> clang_sys::CXChildVisitResult {
     if !filter_builtins(ctx, &cursor) {

• Run rustfmt-format-diff.py, which as of right now it does:

rustfmt --file-lines '[{"range": [1268, 1274], "file": "src/lib.rs"}]' src/lib.rs

Expected: Only the parse_one signature is modified.

Actual: A lot of use statements and whitespace is missing, and also lines with comments misindented.

[emilio]

This helps not to get them skipped, but the use statements still get reformatted / reordered:

diff --git a/src/utils.rs b/src/utils.rs
index 9c1717e..47ce5e7 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -343,6 +343,7 @@ macro_rules! skip_out_of_file_lines_range {
 macro_rules! skip_out_of_file_lines_range_visitor {
     ($self:ident, $span:expr) => {
         if out_of_file_lines_range!($self, $span) {
+            $self.push_rewrite($span, None);
             return;
         }
     }

Disclaimer, no clue about whether it's the right fix :-)

[emilio]

Ok, I also got a patch for the other issue, I'll try to add some tests :-)

[emilio]

I opened #1841 with my fixes on top of this.

Also, thanks @topecongiro! I was about to report too much stuff being formatted with file-lines, and you already had a fix up for review, that's awesome! :)

[nrc]

Thanks for the changes!