Improve &pin reference-pattern suggestions

[P8L1]

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This fills in the pin_ergonomics FIXME in borrow_pat_suggestion by making the diagnostic prefix account for both Pinnedness and Mutability.

Previously, the type-position suggestion path used ordinary reference spelling, which can spell & and &mut but cannot correctly spell pinned reference-pattern suggestions such as &pin const and &pin mut.

This is a diagnostic-only change. It adds focused UI coverage for both pinned const and pinned mut reference-pattern suggestions.

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[mu001999]

r? Kivooeo

[Kivooeo]

two things i think should be improved

1. currently it make suggestion to a code, that requires pin_ergonomics feature to work, so imo this suggestion should only emits when this feature is enabled (i don't know if there is a way to check so)
2. i don't sure if this code only works on nightly or not? this suggestion have zero meaning on stable

so, if we can't check 1 point then i'd say to wait on stabilization of this feature, and then fix that fixme

[Kivooeo]

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[P8L1]

two things i think should be improved

1. currently it make suggestion to a code, that requires pin_ergonomics feature to work, so imo this suggestion should only emits when this feature is enabled (i don't know if there is a way to check so)
2. i don't sure if this code only works on nightly or not? this suggestion have zero meaning on stable

so, if we can't check 1 point then i'd say to wait on stabilization of this feature, and then fix that fixme

Thanks for the suggestion. I gated the type-position &pin suggestion on pin_ergonomics, so crates without the feature fall back to the existing non-pin reference suggestion instead.

[Kivooeo]

This diff could be simplified, looks slightly over-engineered. Here's a leaner approach:

diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index d7f15222376..604beb6da3c 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -1407,6 +1407,11 @@ fn borrow_pat_suggestion(&self, err: &mut Diag<'_>, pat: &Pat<'_>) {
             };
 
             match binding_parent {
+                // FIXME(pin_ergnomics): we currenty skip suggestion if feature is not enabled
+                // because the correct suggestion requeiers feature to be enabled
+                // so we want only ask user to enable feature
+                hir::Node::Param(hir::Param { ty_span, pat, .. })
+                    if pat.span != *ty_span && !tcx.features().pin_ergonomics() => {}
                 // Check that there is explicit type (ie this is not a closure param with inferred type)
                 // so we don't suggest moving something to the type that does not exist
                 hir::Node::Param(hir::Param { ty_span, pat, .. }) if pat.span != *ty_span => {
@@ -1414,7 +1419,7 @@ fn borrow_pat_suggestion(&self, err: &mut Diag<'_>, pat: &Pat<'_>) {
                         format!("to take parameter `{binding}` by reference, move `&{pin_and_mut}` to the type"),
                         vec![
                             (pat.span.until(inner.span), "".to_owned()),
-                            (ty_span.shrink_to_lo(), mutbl.ref_prefix_str().to_owned()),
+                            (ty_span.shrink_to_lo(), format!("&{}", pinned.prefix_str(mutbl))),
                         ],
                         Applicability::MachineApplicable
                     );

[P8L1]

This diff could be simplified, looks slightly over-engineered. Here's a leaner approach:

diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index d7f15222376..604beb6da3c 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -1407,6 +1407,11 @@ fn borrow_pat_suggestion(&self, err: &mut Diag<'_>, pat: &Pat<'_>) {
             };
 
             match binding_parent {
+                // FIXME(pin_ergnomics): we currenty skip suggestion if feature is not enabled
+                // because the correct suggestion requeiers feature to be enabled
+                // so we want only ask user to enable feature
+                hir::Node::Param(hir::Param { ty_span, pat, .. })
+                    if pat.span != *ty_span && !tcx.features().pin_ergonomics() => {}
                 // Check that there is explicit type (ie this is not a closure param with inferred type)
                 // so we don't suggest moving something to the type that does not exist
                 hir::Node::Param(hir::Param { ty_span, pat, .. }) if pat.span != *ty_span => {
@@ -1414,7 +1419,7 @@ fn borrow_pat_suggestion(&self, err: &mut Diag<'_>, pat: &Pat<'_>) {
                         format!("to take parameter `{binding}` by reference, move `&{pin_and_mut}` to the type"),
                         vec![
                             (pat.span.until(inner.span), "".to_owned()),
-                            (ty_span.shrink_to_lo(), mutbl.ref_prefix_str().to_owned()),
+                            (ty_span.shrink_to_lo(), format!("&{}", pinned.prefix_str(mutbl))),
                         ],
                         Applicability::MachineApplicable
                     );

Thanks, simplified this along those lines.

I kept the feature-gate arm limited to pinned reference patterns so ordinary & / &mut suggestions are not suppressed when pin_ergonomics is disabled. The pinned type-position suggestion is skipped without the feature gate, and the &pin mut / &pin const suggestions are still emitted when the feature is enabled.

I also kept the stabilization FIXME and re-blessed the affected UI output.

[Kivooeo]

@bors squash

[rust-bors]

🔨 9 commits were squashed into 14d414b.

[Kivooeo]

@bors r+ rollup

[rust-bors]

📌 Commit 14d414b has been approved by Kivooeo

It is now in the queue for this repository.