Add an option to remove reborrows from adjustment inlay hints

Reborrows are consecutive deref then ref. Make it the default because reborrows are mostly useless to the programmer.

Also rename `rust-analyzer.inlayHints.expressionAdjustmentHints.enable: "reborrow"` to `rust-analyzer.inlayHints.expressionAdjustmentHints.enable: "borrows"`, as it's not about reborrows but about any ref/deref and it's confusing with the new setting.

crates/ide/src/inlay_hints.rs

@@ -306,6 +306,7 @@ pub struct InlayHintsConfig {
     pub generic_parameter_hints: GenericParameterHints,
     pub chaining_hints: bool,
     pub adjustment_hints: AdjustmentHints,
+    pub adjustment_hints_disable_reborrows: bool,
     pub adjustment_hints_mode: AdjustmentHintsMode,
     pub adjustment_hints_hide_outside_unsafe: bool,
     pub closure_return_type_hints: ClosureReturnTypeHints,
@@ -430,7 +431,7 @@ pub enum LifetimeElisionHints {
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum AdjustmentHints {
     Always,
-    ReborrowOnly,
+    BorrowsOnly,
     Never,
 }
 
@@ -886,6 +887,7 @@ mod tests {
         closure_return_type_hints: ClosureReturnTypeHints::Never,
         closure_capture_hints: false,
         adjustment_hints: AdjustmentHints::Never,
+        adjustment_hints_disable_reborrows: false,
         adjustment_hints_mode: AdjustmentHintsMode::Prefix,
         adjustment_hints_hide_outside_unsafe: false,
         binding_mode_hints: false,

crates/ide/src/inlay_hints/adjustment.rs

@@ -47,7 +47,22 @@ pub(super) fn hints(
 
     let descended = sema.descend_node_into_attributes(expr.clone()).pop();
     let desc_expr = descended.as_ref().unwrap_or(expr);
-    let adjustments = sema.expr_adjustments(desc_expr).filter(|it| !it.is_empty())?;
+    let mut adjustments = sema.expr_adjustments(desc_expr).filter(|it| !it.is_empty())?;
+
+    if config.adjustment_hints_disable_reborrows {
+        // Remove consecutive deref-ref, i.e. reborrows.
+        let mut i = 0;
+        while i < adjustments.len().saturating_sub(1) {
+            let [current, next, ..] = &adjustments[i..] else { unreachable!() };
+            if matches!(current.kind, Adjust::Deref(None))
+                && matches!(next.kind, Adjust::Borrow(AutoBorrow::Ref(_)))
+            {
+                adjustments.splice(i..i + 2, []);
+            } else {
+                i += 1;
+            }
+        }
+    }
 
     if let ast::Expr::BlockExpr(_) | ast::Expr::IfExpr(_) | ast::Expr::MatchExpr(_) = desc_expr {
         // Don't show unnecessary reborrows for these, they will just repeat the inner ones again
@@ -716,6 +731,38 @@ fn hello(it: &&[impl T]) {
   //^^(&**
   //^^)
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn disable_reborrows() {
+        check_with_config(
+            InlayHintsConfig {
+                adjustment_hints: AdjustmentHints::Always,
+                adjustment_hints_disable_reborrows: true,
+                ..DISABLED_CONFIG
+            },
+            r#"
+#![rustc_coherence_is_core]
+
+trait ToOwned {
+    type Owned;
+    fn to_owned(&self) -> Self::Owned;
+}
+
+struct String;
+impl ToOwned for str {
+    type Owned = String;
+    fn to_owned(&self) -> Self::Owned { String }
+}
+
+fn a(s: &String) {}
+
+fn main() {
+    let s = "".to_owned();
+    a(&s)
+}
 "#,
         );
     }

crates/ide/src/static_index.rs

@@ -169,6 +169,7 @@ impl StaticIndex<'_> {
                     closure_return_type_hints: crate::ClosureReturnTypeHints::WithBlock,
                     lifetime_elision_hints: crate::LifetimeElisionHints::Never,
                     adjustment_hints: crate::AdjustmentHints::Never,
+                    adjustment_hints_disable_reborrows: true,
                     adjustment_hints_mode: AdjustmentHintsMode::Prefix,
                     adjustment_hints_hide_outside_unsafe: false,
                     implicit_drop_hints: false,

crates/rust-analyzer/src/cli/analysis_stats.rs

@@ -1137,6 +1137,7 @@ impl flags::AnalysisStats {
                     },
                     chaining_hints: true,
                     adjustment_hints: ide::AdjustmentHints::Always,
+                    adjustment_hints_disable_reborrows: true,
                     adjustment_hints_mode: ide::AdjustmentHintsMode::Postfix,
                     adjustment_hints_hide_outside_unsafe: false,
                     closure_return_type_hints: ide::ClosureReturnTypeHints::Always,

crates/rust-analyzer/src/config.rs

@@ -226,6 +226,14 @@ config_data! {
         inlayHints_discriminantHints_enable: DiscriminantHintsDef =
             DiscriminantHintsDef::Never,
 
+        /// Disable reborrows in expression adjustments inlay hints.
+        ///
+        /// Reborrows are a pair of a builtin deref then borrow, i.e. `&*`. They are inserted by the compiler but are mostly useless to the programmer.
+        ///
+        /// Note: if the deref is not builtin (an overloaded deref), or the borrow is `&raw const`/`&raw mut`, they are not removed.
+        inlayHints_expressionAdjustmentHints_disableReborrows: bool =
+            true,
+
         /// Show inlay hints for type adjustments.
         inlayHints_expressionAdjustmentHints_enable: AdjustmentHintsDef =
             AdjustmentHintsDef::Never,
@@ -1888,12 +1896,14 @@ impl Config {
                 AdjustmentHintsDef::Always => ide::AdjustmentHints::Always,
                 AdjustmentHintsDef::Never => match self.inlayHints_reborrowHints_enable() {
                     ReborrowHintsDef::Always | ReborrowHintsDef::Mutable => {
-                        ide::AdjustmentHints::ReborrowOnly
+                        ide::AdjustmentHints::BorrowsOnly
                     }
                     ReborrowHintsDef::Never => ide::AdjustmentHints::Never,
                 },
-                AdjustmentHintsDef::Reborrow => ide::AdjustmentHints::ReborrowOnly,
+                AdjustmentHintsDef::Borrows => ide::AdjustmentHints::BorrowsOnly,
             },
+            adjustment_hints_disable_reborrows: *self
+                .inlayHints_expressionAdjustmentHints_disableReborrows(),
             adjustment_hints_mode: match self.inlayHints_expressionAdjustmentHints_mode() {
                 AdjustmentHintsModeDef::Prefix => ide::AdjustmentHintsMode::Prefix,
                 AdjustmentHintsModeDef::Postfix => ide::AdjustmentHintsMode::Postfix,
@@ -2822,7 +2832,8 @@ enum ReborrowHintsDef {
 #[derive(Serialize, Deserialize, Debug, Clone)]
 #[serde(rename_all = "snake_case")]
 enum AdjustmentHintsDef {
-    Reborrow,
+    #[serde(alias = "Reborrow")]
+    Borrows,
     #[serde(with = "true_or_always")]
     #[serde(untagged)]
     Always,

docs/book/src/configuration_generated.md

@@ -959,6 +959,17 @@ Default: `"never"`
 Show enum variant discriminant hints.
 
 
+## rust-analyzer.inlayHints.expressionAdjustmentHints.disableReborrows {#inlayHints.expressionAdjustmentHints.disableReborrows}
+
+Default: `true`
+
+Disable reborrows in expression adjustments inlay hints.
+
+Reborrows are a pair of a builtin deref then borrow, i.e. `&*`. They are inserted by the compiler but are mostly useless to the programmer.
+
+Note: if the deref is not builtin (an overloaded deref), or the borrow is `&raw const`/`&raw mut`, they are not removed.
+
+
 ## rust-analyzer.inlayHints.expressionAdjustmentHints.enable {#inlayHints.expressionAdjustmentHints.enable}
 
 Default: `"never"`

editors/code/package.json

@@ -2209,6 +2209,16 @@
                     }
                 }
             },
+            {
+                "title": "Inlay Hints",
+                "properties": {
+                    "rust-analyzer.inlayHints.expressionAdjustmentHints.disableReborrows": {
+                        "markdownDescription": "Disable reborrows in expression adjustments inlay hints.\n\nReborrows are a pair of a builtin deref then borrow, i.e. `&*`. They are inserted by the compiler but are mostly useless to the programmer.\n\nNote: if the deref is not builtin (an overloaded deref), or the borrow is `&raw const`/`&raw mut`, they are not removed.",
+                        "default": true,
+                        "type": "boolean"
+                    }
+                }
+            },
             {
                 "title": "Inlay Hints",
                 "properties": {