Regression: Inappropriate attribute removal causes incorrect code generation

[ppannuto]

v0.6.3 does not touch this code, v0.7.1 removes only the first instance of #[no_mangle]

The following is a reduced test case that silently (no compile error) broke the kernel. Original file here.

Input

#![crate_name = "sam4l"]
#![crate_type = "rlib"]
#![feature(asm,core_intrinsics,concat_idents,const_fn)]
#![no_std]

#[link_section=".vectors"]
#[no_mangle] // Ensures that the symbol is kept until the final binary
#[cfg_attr(rustfmt, rustfmt_skip)]
pub static BASE_VECTORS: [unsafe extern fn(); 16] = [
    _estack, reset_handler,
    /* NMI */           unhandled_interrupt,
    /* Hard Fault */    hard_fault_handler,
];

#[link_section=".vectors"]
#[no_mangle] // Ensures that the symbol is kept until the final binary
pub static IRQS: [unsafe extern "C" fn(); 80] = [generic_isr; 80];

#[no_mangle]
#[cfg_attr(rustfmt, rustfmt_skip)]
pub static INTERRUPT_TABLE: [Option<unsafe extern fn()>; 80] = [
    /* HFLASHC */       Option::Some(flashcalw::flash_handler),
    /* PDCA0 */         Option::Some(dma::pdca0_handler),
    /* PDCA1 */         Option::Some(dma::pdca1_handler),
];

Output

#![crate_name = "sam4l"]
#![crate_type = "rlib"]
#![feature(asm,core_intrinsics,concat_idents,const_fn)]
#![no_std]

#[link_section=".vectors"]
 // Ensures that the symbol is kept until the final binary
#[cfg_attr(rustfmt, rustfmt_skip)]
pub static BASE_VECTORS: [unsafe extern fn(); 16] = [
    _estack, reset_handler,
    /* NMI */           unhandled_interrupt,
    /* Hard Fault */    hard_fault_handler,
];

#[link_section=".vectors"]
#[no_mangle] // Ensures that the symbol is kept until the final binary
pub static IRQS: [unsafe extern "C" fn(); 80] = [generic_isr; 80];

#[no_mangle]
#[cfg_attr(rustfmt, rustfmt_skip)]
pub static INTERRUPT_TABLE: [Option<unsafe extern fn()>; 80] = [
    /* HFLASHC */       Option::Some(flashcalw::flash_handler),
    /* PDCA0 */         Option::Some(dma::pdca0_handler),
    /* PDCA1 */         Option::Some(dma::pdca1_handler),
];

While the exact line #[no_mangle] // Ensures that the symbol is kept until the final binary appears twice, in the first case it is followed by #[cfg_attr(rustfmt, rustfmt_skip)]. Removing that cfg causes rustfmt to leave the no_mangle alone. Interestingly, the third case also has the skip cfg, but no comment after the no_mangle and is unaffected. Deleting the comment after the first no_mangle also fixes this issue.