1 files changed, 142 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide/src/inlay_hints/binding_mode.rs b/src/tools/rust-analyzer/crates/ide/src/inlay_hints/binding_mode.rs
new file mode 100644
index 000000000..a0166d004
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide/src/inlay_hints/binding_mode.rs
@@ -0,0 +1,142 @@
+//! Implementation of "binding mode" inlay hints:
+//! ```no_run
+//! let /* & */ (/* ref */ x,) = &(0,);
+//! ```
+use hir::{Mutability, Semantics};
+use ide_db::RootDatabase;
+
+use syntax::ast::{self, AstNode};
+
+use crate::{InlayHint, InlayHintsConfig, InlayKind, InlayTooltip};
+
+pub(super) fn hints(
+    acc: &mut Vec<InlayHint>,
+    sema: &Semantics<'_, RootDatabase>,
+    config: &InlayHintsConfig,
+    pat: &ast::Pat,
+) -> Option<()> {
+    if !config.binding_mode_hints {
+        return None;
+    }
+
+    let outer_paren_pat = pat
+        .syntax()
+        .ancestors()
+        .skip(1)
+        .map_while(ast::Pat::cast)
+        .map_while(|pat| match pat {
+            ast::Pat::ParenPat(pat) => Some(pat),
+            _ => None,
+        })
+        .last();
+    let range =
+        outer_paren_pat.as_ref().map_or_else(|| pat.syntax(), |it| it.syntax()).text_range();
+    let pattern_adjustments = sema.pattern_adjustments(pat);
+    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,
+        };
+        acc.push(InlayHint {
+            range,
+            kind: InlayKind::BindingModeHint,
+            label: r.to_string().into(),
+            tooltip: Some(InlayTooltip::String("Inferred binding mode".into())),
+        });
+    });
+    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 => return None,
+                hir::BindingMode::Ref(Mutability::Mut) => "ref mut",
+                hir::BindingMode::Ref(Mutability::Shared) => "ref",
+            };
+            acc.push(InlayHint {
+                range: pat.syntax().text_range(),
+                kind: InlayKind::BindingModeHint,
+                label: bm.to_string().into(),
+                tooltip: Some(InlayTooltip::String("Inferred binding mode".into())),
+            });
+        }
+        ast::Pat::OrPat(pat) if !pattern_adjustments.is_empty() && outer_paren_pat.is_none() => {
+            acc.push(InlayHint {
+                range: pat.syntax().text_range(),
+                kind: InlayKind::OpeningParenthesis,
+                label: "(".into(),
+                tooltip: None,
+            });
+            acc.push(InlayHint {
+                range: pat.syntax().text_range(),
+                kind: InlayKind::ClosingParenthesis,
+                label: ")".into(),
+                tooltip: None,
+            });
+        }
+        _ => (),
+    }
+
+    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
+) {
+    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
+    }
+}"#,
+        );
+    }
+}