Correct "expected"/"found" on assert! type errors

Author: estebank

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

@@ -1596,8 +1596,16 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         {
             let e = self.tcx.erase_regions(e);
             let f = self.tcx.erase_regions(f);
-            let expected = with_forced_trimmed_paths!(e.sort_string(self.tcx));
-            let found = with_forced_trimmed_paths!(f.sort_string(self.tcx));
+            let mut expected = with_forced_trimmed_paths!(e.sort_string(self.tcx));
+            let mut found = with_forced_trimmed_paths!(f.sort_string(self.tcx));
+            if let Some(def_id) = cause.span.ctxt().outer_expn_data().macro_def_id
+                && self.tcx.is_diagnostic_item(sym::assert_macro, def_id)
+            {
+                // When the type error comes from `assert!()`, the cause and effect are reversed
+                // because that macro expands to `match val { false => {panic!()}, _ => {} }`, which
+                // would say something like "expected `Type`, found `bool`", confusing the user.
+                (found, expected) = (expected, found);
+            }
             if expected == found {
                 label_or_note(span, terr.to_string(self.tcx));
             } else {
@@ -2114,7 +2122,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
     ) -> Option<(DiagStyledString, DiagStyledString, Option<PathBuf>)> {
         match values {
             ValuePairs::Regions(exp_found) => self.expected_found_str(exp_found),
-            ValuePairs::Terms(exp_found) => self.expected_found_str_term(exp_found),
+            ValuePairs::Terms(exp_found) => self.expected_found_str_term(cause, exp_found),
             ValuePairs::Aliases(exp_found) => self.expected_found_str(exp_found),
             ValuePairs::ExistentialTraitRef(exp_found) => self.expected_found_str(exp_found),
             ValuePairs::ExistentialProjection(exp_found) => self.expected_found_str(exp_found),
@@ -2155,14 +2163,26 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
     fn expected_found_str_term(
         &self,
+        cause: &ObligationCause<'tcx>,
         exp_found: ty::error::ExpectedFound<ty::Term<'tcx>>,
     ) -> Option<(DiagStyledString, DiagStyledString, Option<PathBuf>)> {
         let exp_found = self.resolve_vars_if_possible(exp_found);
         if exp_found.references_error() {
             return None;
         }
+        let (mut expected, mut found) = (exp_found.expected, exp_found.found);
+        if let Some(def_id) = cause.span.ctxt().outer_expn_data().macro_def_id
+            && self.tcx.is_diagnostic_item(sym::assert_macro, def_id)
+        {
+            // When the type error comes from `assert!()`, the cause and effect are reversed
+            // because that macro expands to `match val { false => {panic!()}, _ => {} }`, which
+            // would say something like
+            // = note: expected `Type`
+            //            found `bool`"
+            (expected, found) = (found, expected);
+        }
 
-        Some(match (exp_found.expected.unpack(), exp_found.found.unpack()) {
+        Some(match (expected.unpack(), found.unpack()) {
             (ty::TermKind::Ty(expected), ty::TermKind::Ty(found)) => {
                 let (mut exp, mut fnd) = self.cmp(expected, found);
                 // Use the terminal width as the basis to determine when to compress the printed

tests/ui/codemap_tests/issue-28308.rs

@@ -1,4 +1,16 @@
 fn main() {
-    assert!("foo");
-    //~^ ERROR mismatched types
+    assert!("foo"); //~ ERROR mismatched types
+    //~^ NOTE expected `bool`, found `str`
+    //~| NOTE in this expansion of assert!
+    let x = Some(&1);
+    assert!(x); //~ ERROR mismatched types
+    //~^ NOTE expected `bool`, found `Option<&{integer}>`
+    //~| NOTE expected enum `bool`
+    //~| NOTE in this expansion of assert!
+    //~| NOTE in this expansion of assert!
+    assert!(x, ""); //~ ERROR mismatched types
+    //~^ NOTE expected `bool`, found `Option<&{integer}>`
+    //~| NOTE expected enum `bool`
+    //~| NOTE in this expansion of assert!
+    //~| NOTE in this expansion of assert!
 }

tests/ui/codemap_tests/issue-28308.stderr

@@ -2,10 +2,30 @@ error[E0308]: mismatched types
   --> $DIR/issue-28308.rs:2:13
    |
 LL |     assert!("foo");
-   |             ^^^^^ expected `str`, found `bool`
+   |             ^^^^^ expected `bool`, found `str`
    |
    = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 1 previous error
+error[E0308]: mismatched types
+  --> $DIR/issue-28308.rs:6:13
+   |
+LL |     assert!(x);
+   |             ^ expected `bool`, found `Option<&{integer}>`
+   |
+   = note: expected enum `bool`
+              found type `Option<&{integer}>`
+   = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/issue-28308.rs:11:13
+   |
+LL |     assert!(x, "");
+   |             ^ expected `bool`, found `Option<&{integer}>`
+   |
+   = note: expected enum `bool`
+              found type `Option<&{integer}>`
+   = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

tests/ui/issues/issue-14091-2.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/issue-14091-2.rs:15:13
    |
 LL |     assert!(x, x);
-   |             ^ expected `BytePos`, found `bool`
+   |             ^ expected `bool`, found `BytePos`
    |
    = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
 

tests/ui/issues/issue-14091.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/issue-14091.rs:2:13
    |
 LL |     assert!(1,1);
-   |             ^ expected integer, found `bool`
+   |             ^ expected `bool`, found integer
    |
    = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)