Fix unuseful span in type error in some format_args!() invocations

compiler/rustc_span/src/span_encoding.rs

@@ -281,6 +281,16 @@ impl Span {
         }
     }
 
+    #[inline]
+    pub fn len(self) -> u32 {
+        (self.len_with_tag_or_marker & !PARENT_TAG) as u32
+    }
+
+    #[inline]
+    pub fn index(self) -> u32 {
+        self.lo_or_index
+    }
+
     #[inline]
     pub fn data(self) -> SpanData {
         let data = self.data_untracked();

compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs

@@ -163,14 +163,26 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         // Ensure `T: Sized` and `T: WF` obligations come last. This lets us display diagnostics
         // with more relevant type information and hide redundant E0282 errors.
         errors.sort_by_key(|e| match e.obligation.predicate.kind().skip_binder() {
+            ty::PredicateKind::Subtype(_)
+                if e.obligation.cause.span.macro_backtrace().next().is_some_and(
+                    |trace| match trace.kind {
+                        ExpnKind::Macro(_, name) => {
+                            name.as_str().rsplit("::").next() == Some("format_args_nl")
+                        }
+                        _ => false,
+                    },
+                ) =>
+            {
+                (-1, e.obligation.cause.span.index())
+            }
             ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred))
                 if self.tcx.is_lang_item(pred.def_id(), LangItem::Sized) =>
             {
-                1
+                (1, 0)
             }
-            ty::PredicateKind::Coerce(_) => 2,
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => 3,
-            _ => 0,
+            ty::PredicateKind::Coerce(_) => (2, 0),
+            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => (3, 0),
+            _ => (0, 0),
         });
 
         for (index, error) in errors.iter().enumerate() {

tests/ui/errors/span-format_args-issue-140578.rs

@@ -0,0 +1,4 @@
+fn main() {
+  println!("{:?} {a} {a:?}", [], a = 1 + 1);
+  //~^ ERROR type annotations needed
+}

tests/ui/errors/span-format_args-issue-140578.stderr

@@ -0,0 +1,11 @@
+error[E0282]: type annotations needed
+  --> $DIR/span-format_args-issue-140578.rs:2:30
+   |
+LL |   println!("{:?} {a} {a:?}", [], a = 1 + 1);
+   |                              ^^ cannot infer type
+   |
+   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.