Fix incorrect trailing comma suggested in no_accessible_fields

Author: chenyukang

compiler/rustc_hir_typeck/src/pat.rs

@@ -2434,10 +2434,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
 
         if let Some(field) = fields.last() {
+            let tail_span = field.span.shrink_to_hi().to(pat.span.shrink_to_hi());
+            let comma_hi_offset =
+                self.tcx.sess.source_map().span_to_snippet(tail_span).ok().and_then(|snippet| {
+                    let trimmed = snippet.trim_start();
+                    trimmed.starts_with(',').then(|| (snippet.len() - trimmed.len() + 1) as u32)
+                });
             err.span_suggestion_verbose(
-                field.span.shrink_to_hi(),
+                if let Some(comma_hi_offset) = comma_hi_offset {
+                    tail_span.with_hi(tail_span.lo() + BytePos(comma_hi_offset)).shrink_to_hi()
+                } else {
+                    field.span.shrink_to_hi()
+                },
                 "ignore the inaccessible and unused fields",
-                ", ..",
+                if comma_hi_offset.is_some() { " .." } else { ", .." },
                 Applicability::MachineApplicable,
             );
         } else {

tests/ui/privacy/inaccessible-private-fields-trailing-comma-149787.fixed

@@ -0,0 +1,23 @@
+#![allow(dead_code)]
+#![allow(unused)]
+//@ run-rustfix
+
+mod m {
+    pub(crate) struct S {
+        pub(crate) visible: u64,
+        hidden: u64,
+    }
+
+    impl S {
+        pub(crate) fn new() -> Self {
+            loop {}
+        }
+    }
+}
+
+fn main() {
+    let m::S {
+        //~^ ERROR pattern requires `..` due to inaccessible fields
+        visible, ..
+    } = m::S::new();
+}

tests/ui/privacy/inaccessible-private-fields-trailing-comma-149787.rs

@@ -0,0 +1,23 @@
+#![allow(dead_code)]
+#![allow(unused)]
+//@ run-rustfix
+
+mod m {
+    pub(crate) struct S {
+        pub(crate) visible: u64,
+        hidden: u64,
+    }
+
+    impl S {
+        pub(crate) fn new() -> Self {
+            loop {}
+        }
+    }
+}
+
+fn main() {
+    let m::S {
+        //~^ ERROR pattern requires `..` due to inaccessible fields
+        visible,
+    } = m::S::new();
+}

tests/ui/privacy/inaccessible-private-fields-trailing-comma-149787.stderr

@@ -0,0 +1,17 @@
+error: pattern requires `..` due to inaccessible fields
+  --> $DIR/inaccessible-private-fields-trailing-comma-149787.rs:19:9
+   |
+LL |       let m::S {
+   |  _________^
+LL | |
+LL | |         visible,
+LL | |     } = m::S::new();
+   | |_____^
+   |
+help: ignore the inaccessible and unused fields
+   |
+LL |         visible, ..
+   |                  ++
+
+error: aborting due to 1 previous error
+