Render some errors a bit more human readably

Author: oli-obk

crates/formality-check/src/coherence.rs

@@ -154,6 +154,6 @@ impl Check<'_> {
 
             return Ok(());
         }
-        bail!("impls may overlap: `{impl_a:?}` vs `{impl_b:?}`")
+        bail!("impls may overlap:\n{impl_a:?}\n{impl_b:?}")
     }
 }

crates/formality-check/src/lib.rs

@@ -149,6 +149,6 @@ impl Check<'_> {
             return Ok(());
         }
 
-        bail!("failed to disprove {goal:?} given {assumptions:?}, got {cs:?}")
+        bail!("failed to disprove\n    {goal:?}\ngiven\n    {assumptions:?}\ngot\n{cs:#?}")
     }
 }

tests/coherence_overlap.rs

@@ -51,12 +51,13 @@ fn test_overlap_normalize_alias_to_LocalType() {
     // ...but it's an error if LocalType implements Iterator (figuring *this* out also
     // requires normalizing).
 
-    expect_test::expect![[r#"
-        Err(
-            "impls may overlap: `impl <ty> LocalTrait < > for ^ty0_0 where [^ty0_0 : Iterator < >] { }` vs `impl <> LocalTrait < > for (alias (Mirror :: T) (rigid (adt LocalType))) where [] { }`",
-        )
-    "#]]
-    .assert_debug_eq(&test_program_ok(&gen_program("impl<> Iterator<> for LocalType<> where [] {}")));
+    expect_test::expect![[r#"Err(
+    "impls may overlap:\nimpl <ty> LocalTrait < > for ^ty0_0 where [^ty0_0 : Iterator < >] { }\nimpl <> LocalTrait < > for (alias (Mirror :: T) (rigid (adt LocalType))) where [] { }",
+)
+"#]]
+    .assert_debug_eq(&test_program_ok(&gen_program(
+        "impl<> Iterator<> for LocalType<> where [] {}",
+    )));
 }
 
 #[test]
@@ -110,11 +111,10 @@ fn test_overlap_alias_not_normalizable() {
 
     // ...as long as there is at least one Iterator impl, however, we do flag an error.
 
-    expect_test::expect![[r#"
-        Err(
-            "impls may overlap: `impl <ty> LocalTrait < > for ^ty0_0 where [^ty0_0 : Iterator < >] { }` vs `impl <ty> LocalTrait < > for (alias (Mirror :: T) ^ty0_0) where [^ty0_0 : Mirror < >] { }`",
-        )
-    "#]] // FIXME
+    expect_test::expect![[r#"Err(
+    "impls may overlap:\nimpl <ty> LocalTrait < > for ^ty0_0 where [^ty0_0 : Iterator < >] { }\nimpl <ty> LocalTrait < > for (alias (Mirror :: T) ^ty0_0) where [^ty0_0 : Mirror < >] { }",
+)
+"#]] // FIXME
     .assert_debug_eq(&test_program_ok(&gen_program(
         "impl<> Iterator<> for u32 where[] {}",
     )));

tests/ui/coherence_overlap/T_where_Foo_not_u32_impls.stderr

@@ -1,4 +1,22 @@
 Error: check_trait_impl(impl <ty> Foo < > for ^ty0_0 where [^ty0_0 : Foo < >] { })
 
 Caused by:
-    failed to disprove {! Foo(!ty_1)} given {Foo(!ty_1)}, got {Constraints { env: Env { variables: [?ty_1], coherence_mode: false }, known_true: true, substitution: {?ty_1 => (rigid (scalar u32))} }}
+    failed to disprove
+        {! Foo(!ty_1)}
+    given
+        {Foo(!ty_1)}
+    got
+    {
+        Constraints {
+            env: Env {
+                variables: [
+                    ?ty_1,
+                ],
+                coherence_mode: false,
+            },
+            known_true: true,
+            substitution: {
+                ?ty_1 => (rigid (scalar u32)),
+            },
+        },
+    }

tests/ui/coherence_overlap/foo_crate_cannot_assume_CoreStruct_does_not_impl_CoreTrait.stderr

@@ -1 +1,3 @@
-Error: impls may overlap: `impl <ty> FooTrait < > for ^ty0_0 where [^ty0_0 : CoreTrait < >] { }` vs `impl <> FooTrait < > for (rigid (adt CoreStruct)) where [] { }`
+Error: impls may overlap:
+impl <ty> FooTrait < > for ^ty0_0 where [^ty0_0 : CoreTrait < >] { }
+impl <> FooTrait < > for (rigid (adt CoreStruct)) where [] { }

tests/ui/coherence_overlap/u32_T_impls.stderr

@@ -1 +1,3 @@
-Error: impls may overlap: `impl <> Foo < > for (rigid (scalar u32)) where [] { }` vs `impl <ty> Foo < > for ^ty0_0 where [] { }`
+Error: impls may overlap:
+impl <> Foo < > for (rigid (scalar u32)) where [] { }
+impl <ty> Foo < > for ^ty0_0 where [] { }

tests/ui/coherence_overlap/u32_T_where_T_Is_impls.stderr

@@ -1 +1,3 @@
-Error: impls may overlap: `impl <> Foo < > for (rigid (scalar u32)) where [] { }` vs `impl <ty> Foo < > for ^ty0_0 where [^ty0_0 : Is < >] { }`
+Error: impls may overlap:
+impl <> Foo < > for (rigid (scalar u32)) where [] { }
+impl <ty> Foo < > for ^ty0_0 where [^ty0_0 : Is < >] { }

tests/ui/coherence_overlap/u32_not_u32_impls.stderr

@@ -1,4 +1,18 @@
 Error: check_trait_impl(impl <> Foo < > for (rigid (scalar u32)) where [] { })
 
 Caused by:
-    failed to disprove {! Foo((rigid (scalar u32)))} given {}, got {Constraints { env: Env { variables: [], coherence_mode: false }, known_true: true, substitution: {} }}
+    failed to disprove
+        {! Foo((rigid (scalar u32)))}
+    given
+        {}
+    got
+    {
+        Constraints {
+            env: Env {
+                variables: [],
+                coherence_mode: false,
+            },
+            known_true: true,
+            substitution: {},
+        },
+    }