"error[internal]: left behind trailing whitespace" reported on code with rightward drift

[camelid]

Describe the bug

rustfmt reports error[internal]: left behind trailing whitespace on this code. Also, in a previous iteration of the code (with the if guards in the body of the match arms instead of being guards), rustfmt failed to format the code without reporting any errors or warnings.

To Reproduce

1. Run rustfmt on this playground code.
2. Observe rustfmt internal errors.

Here's the code (same as in the playground):

impl Foo {
    fn check_doc_attrs(&self, attr: &Attribute, hir_id: HirId, target: Target) -> bool {
        if let Some(list) = attr.meta().and_then(|mi| mi.meta_item_list()) {
            for meta in list {
                if let Some(i_meta) = meta.meta_item() {
                    match i_meta.path {
                        sym::alias
                            if !self.check_attr_crate_level(meta, hir_id, "alias")
                                || !self.check_doc_alias(meta, hir_id, target)=>
                            {
                                return false;
                            }
                         sym::keyword 
                            if !self.check_attr_crate_level(meta, hir_id, "keyword")
                                || !self.check_doc_keyword(meta, hir_id)
                            =>{
                                return false;
                            }
                         sym::test 
                            if CRATE_HIR_ID != hir_id=> {
                                self.tcx.struct_span_lint_hir(
                                    INVALID_DOC_ATTRIBUTES,
                                    hir_id,
                                    meta.span(),
                                    |lint| {
                                        lint.build(
                                            "`#![doc(test(...)]` is only allowed \
                                             as a crate level attribute"
                                        )
                                        .emit();
                                    },
                                );
                                return false;
                            }
                        
                        sym::alias
                        | sym::cfg
                        | sym::hidden
                        | sym::html_favicon_url
                        | sym::html_logo_url
                        | sym::html_no_source
                        | sym::html_playground_url
                        | sym::html_root_url
                        | sym::include
                        | sym::inline
                        | sym::issue_tracker_base_url
                        | sym::keyword
                        | sym::masked
                        | sym::no_default_passes // deprecated
                        | sym::no_inline
                        | sym::passes  // deprecated
                        | sym::plugins // removed, but rustdoc warns about it itself
                        | sym::primitive
                        | sym::spotlight
                        | sym::test => {}
                        _ => {
                            self.tcx.struct_span_lint_hir(
                                INVALID_DOC_ATTRIBUTES,
                                hir_id,
                                i_meta.span,
                                |lint| {
                                    lint.build(&format!(
                                        "unknown `doc` attribute `{}`",
                                        i_meta.name_or_empty()
                                    ))
                                    .emit();
                                },
                            );
                            return false;
                        }
                    }
                }
            }
        }
        true
    }
}

And here's the output:

error[internal]: left behind trailing whitespace
  --> /playground/src/main.rs:13:13:37
   |
13 |                          sym::keyword 
   |                                      ^
   |

error[internal]: left behind trailing whitespace
  --> /playground/src/main.rs:19:19:34
   |
19 |                          sym::test 
   |                                   ^
   |

error[internal]: left behind trailing whitespace
  --> /playground/src/main.rs:35:35:0
   |
35 |                         
   | ^^^^^^^^^^^^^^^^^^^^^^^^
   |

warning: rustfmt has failed to format. See previous 3 errors.

Expected behavior

The code should be formatted correctly and no errors should be reported.

Meta

• rustfmt version: 1.4.36-nightly (2021-02-07 7de6968) (current playground version)
• From where did you install rustfmt?: rust-lang/rust x.py as well as Rust Playground
• How do you run rustfmt: x.py and playground

[camelid]

I manually removed the whitespace but rustfmt still isn't formatting the new code, though it stopped reporting errors.

[calebcartwright]

Thanks for sharing, though closing as duplicate because the root cause is the same as #4119. If you remove those line-style comments between the patterns towards the end (e.g. // deprecated) then rustfmt will carry on happily.