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

Author: moatom

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

@@ -7,6 +7,7 @@ pub mod on_unimplemented_format;
 mod overflow;
 pub mod suggestions;
 
+use std::cmp::Reverse;
 use std::{fmt, iter};
 
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
@@ -136,6 +137,17 @@ pub enum DefIdOrName {
     Name(&'static str),
 }
 
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+enum ErrorSortKey {
+    SubtypeFormat(Reverse<usize>),
+    OtherKind,
+    SizedTrait,
+    MetaSizedTrait,
+    PointeeSizedTrait,
+    Coerce,
+    ClauseWellFormed,
+}
+
 impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     pub fn report_fulfillment_errors(
         &self,
@@ -170,13 +182,39 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 _ => None,
             };
 
+
+            let span = e.obligation.cause.span;
+            let outer_expn_data = span.ctxt().outer_expn_data();
+
             match e.obligation.predicate.kind().skip_binder() {
-                _ if maybe_sizedness_did == self.tcx.lang_items().sized_trait() => 1,
-                _ if maybe_sizedness_did == self.tcx.lang_items().meta_sized_trait() => 2,
-                _ if maybe_sizedness_did == self.tcx.lang_items().pointee_sized_trait() => 3,
-                ty::PredicateKind::Coerce(_) => 4,
-                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => 5,
-                _ => 0,
+                ty::PredicateKind::Subtype(_)
+                    if matches! (
+                        outer_expn_data.kind,
+                        ExpnKind::Macro(_, name) if matches!(
+                            name.as_str().rsplit("::").next(),
+                            Some("format_args" | "format_args_nl")
+                        )
+                    ) =>
+                {
+                    let sm = self.tcx.sess.source_map();
+                    let lc = sm.span_to_location_info(span);
+
+                    if sm.span_to_embeddable_string(span)
+                        == sm.span_to_embeddable_string(outer_expn_data.call_site)
+                    {
+                        ErrorSortKey::OtherKind
+                    } else {
+                        ErrorSortKey::SubtypeFormat(Reverse(lc.2))
+                    }
+                }
+                _ if maybe_sizedness_did == self.tcx.lang_items().sized_trait() => ErrorSortKey::SizedTrait,
+                _ if maybe_sizedness_did == self.tcx.lang_items().meta_sized_trait() => ErrorSortKey::MetaSizedTrait,
+                _ if maybe_sizedness_did == self.tcx.lang_items().pointee_sized_trait() => ErrorSortKey::PointeeSizedTrait,
+                ty::PredicateKind::Coerce(_) => ErrorSortKey::Coerce,
+                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_)) => {
+                    ErrorSortKey::ClauseWellFormed
+                }
+                _ => ErrorSortKey::OtherKind,
             }
         });
 

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

@@ -0,0 +1,11 @@
+fn check_format_args() {
+  print!("{:?} {a} {a:?}", [], a = 1 + 1);
+  //~^ ERROR type annotations needed
+}
+
+fn check_format_args_nl() {
+  println!("{:?} {a} {a:?}", [], a = 1 + 1);
+  //~^ ERROR type annotations needed
+}
+
+fn main() {}

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

@@ -0,0 +1,19 @@
+error[E0282]: type annotations needed
+  --> $DIR/span-format_args-issue-140578.rs:2:28
+   |
+LL |   print!("{:?} {a} {a:?}", [], a = 1 + 1);
+   |                            ^^ cannot infer type
+   |
+   = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the macro `print` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0282]: type annotations needed
+  --> $DIR/span-format_args-issue-140578.rs:7:30
+   |
+LL |   println!("{:?} {a} {a:?}", [], a = 1 + 1);
+   |                              ^^ cannot infer type
+   |
+   = note: this error originates in the macro `$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 2 previous errors
+
+For more information about this error, try `rustc --explain E0282`.