ide/inlay_hints/
binding_mode.rs

//! Implementation of "binding mode" inlay hints:
//! ```no_run
//! let /* & */ (/* ref */ x,) = &(0,);
//! ```
use std::mem;

use hir::Mutability;
use ide_db::famous_defs::FamousDefs;

use ide_db::text_edit::TextEditBuilder;
use span::EditionedFileId;
use syntax::ast::{self, AstNode};

use crate::{InlayHint, InlayHintLabel, InlayHintPosition, InlayHintsConfig, InlayKind};

pub(super) fn hints(
    acc: &mut Vec<InlayHint>,
    FamousDefs(sema, _): &FamousDefs<'_, '_>,
    config: &InlayHintsConfig,
    _file_id: EditionedFileId,
    pat: &ast::Pat,
) -> Option<()> {
    if !config.binding_mode_hints {
        return None;
    }

    let outer_paren_pat = pat.syntax().ancestors().skip(1).map_while(ast::ParenPat::cast).last();
    let range = outer_paren_pat.as_ref().map_or_else(
        || match pat {
            // for ident patterns that @ bind a name, render the un-ref patterns in front of the inner pattern
            // instead of the name as that makes it more clear and doesn't really change the outcome
            ast::Pat::IdentPat(it) => {
                it.pat().map_or_else(|| it.syntax().text_range(), |it| it.syntax().text_range())
            }
            it => it.syntax().text_range(),
        },
        |it| it.syntax().text_range(),
    );
    let mut hint = InlayHint {
        range,
        kind: InlayKind::BindingMode,
        label: InlayHintLabel::default(),
        text_edit: None,
        position: InlayHintPosition::Before,
        pad_left: false,
        pad_right: false,
        resolve_parent: Some(pat.syntax().text_range()),
    };
    let pattern_adjustments = sema.pattern_adjustments(pat);
    let mut was_mut_last = false;
    pattern_adjustments.iter().for_each(|ty| {
        let reference = ty.is_reference();
        let mut_reference = ty.is_mutable_reference();
        let r = match (reference, mut_reference) {
            (true, true) => "&mut",
            (true, false) => "&",
            _ => return,
        };
        if mem::replace(&mut was_mut_last, mut_reference) {
            hint.label.append_str(" ");
        }
        hint.label.append_str(r);
    });
    hint.pad_right = was_mut_last;
    let acc_base = acc.len();
    match pat {
        ast::Pat::IdentPat(pat) if pat.ref_token().is_none() && pat.mut_token().is_none() => {
            let bm = sema.binding_mode_of_pat(pat)?;
            let bm = match bm {
                hir::BindingMode::Move => None,
                hir::BindingMode::Ref(Mutability::Mut) => Some("ref mut"),
                hir::BindingMode::Ref(Mutability::Shared) => Some("ref"),
            };
            if let Some(bm) = bm {
                acc.push(InlayHint {
                    range: pat.syntax().text_range(),
                    kind: InlayKind::BindingMode,
                    label: bm.into(),
                    text_edit: None,
                    position: InlayHintPosition::Before,
                    pad_left: false,
                    pad_right: true,
                    resolve_parent: Some(pat.syntax().text_range()),
                });
            }
        }
        ast::Pat::OrPat(pat) if !pattern_adjustments.is_empty() && outer_paren_pat.is_none() => {
            hint.label.append_str("(");
            acc.push(InlayHint::closing_paren_after(
                InlayKind::BindingMode,
                pat.syntax().text_range(),
            ));
        }
        _ => (),
    }
    if !hint.label.parts.is_empty() {
        acc.push(hint);
    }

    if let hints @ [_, ..] = &mut acc[acc_base..] {
        let mut edit = TextEditBuilder::default();
        for h in &mut *hints {
            edit.insert(
                match h.position {
                    InlayHintPosition::Before => h.range.start(),
                    InlayHintPosition::After => h.range.end(),
                },
                h.label.parts.iter().map(|p| &*p.text).collect(),
            );
        }
        let edit = edit.finish();
        hints.iter_mut().for_each(|h| h.text_edit = Some(edit.clone()));
    }

    Some(())
}

#[cfg(test)]
mod tests {
    use crate::{
        inlay_hints::tests::{check_with_config, DISABLED_CONFIG},
        InlayHintsConfig,
    };

    #[test]
    fn hints_binding_modes() {
        check_with_config(
            InlayHintsConfig { binding_mode_hints: true, ..DISABLED_CONFIG },
            r#"
fn __(
    (x,): (u32,),
    (x,): &(u32,),
  //^^^^&
   //^ ref
    (x,): &mut (u32,)
  //^^^^&mut
   //^ ref mut
   (x,): &mut &mut (u32,)
 //^^^^&mut &mut
  //^ ref mut
   (x,): &&(u32,)
 //^^^^&&
  //^ ref

) {
    let (x,) = (0,);
    let (x,) = &(0,);
      //^^^^ &
       //^ ref
    let (x,) = &mut (0,);
      //^^^^ &mut
       //^ ref mut
    let &mut (x,) = &mut (0,);
    let (ref mut x,) = &mut (0,);
      //^^^^^^^^^^^^ &mut
    let &mut (ref mut x,) = &mut (0,);
    let (mut x,) = &mut (0,);
      //^^^^^^^^ &mut
    match (0,) {
        (x,) => ()
    }
    match &(0,) {
        (x,) | (x,) => (),
      //^^^^^^^^^^^)
      //^^^^^^^^^^^&(
       //^ ref
              //^ ref
        ((x,) | (x,)) => (),
      //^^^^^^^^^^^^^&
        //^ ref
               //^ ref
    }
    match &mut (0,) {
        (x,) => ()
      //^^^^ &mut
       //^ ref mut
    }
}"#,
        );
    }

    #[test]
    fn hints_binding_modes_complex_ident_pat() {
        check_with_config(
            InlayHintsConfig { binding_mode_hints: true, ..DISABLED_CONFIG },
            r#"
struct Struct {
    field: &'static str,
}
fn foo(s @ Struct { field, .. }: &Struct) {}
         //^^^^^^^^^^^^^^^^^^^^&
                  //^^^^^ref
"#,
        );
    }
}
ide/inlay_hints/binding_mode.rs

ide/inlay_hints/
binding_mode.rs
