From ef77ff35cf48b98244c83ef3c398a38fff9bb8cb Mon Sep 17 00:00:00 2001
From: ayazhafiz <ayaz.hafiz.1@gmail.com>
Date: Thu, 5 May 2022 21:14:54 -0400
Subject: [PATCH] Improve expectation for platform requires mismatch
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```
── TYPE MISMATCH ───── examples/hello-world/rust-platform/./Package-Config.roc ─

Something is off with the type annotation of the main required symbol:

2│      requires {} { main : a -> a }
                             ^^^^^^

This #UserApp.main value is a:

    Str

But the type annotation on main says it should be:

    a -> a

────────────────────────────────────────────────────────────────────────────────
```
---
 compiler/constrain/src/module.rs | 2 +-
 compiler/types/src/types.rs      | 4 ++++
 reporting/src/error/type.rs      | 6 ++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/compiler/constrain/src/module.rs b/compiler/constrain/src/module.rs
index 60700cbe35..0051a7049e 100644
--- a/compiler/constrain/src/module.rs
+++ b/compiler/constrain/src/module.rs
@@ -155,7 +155,7 @@ fn constrain_symbols_from_requires(
                     Expected::FromAnnotation(
                         loc_symbol.map(|&s| Pattern::Identifier(s)),
                         arity,
-                        AnnotationSource::TypedBody {
+                        AnnotationSource::RequiredSymbol {
                             region: loc_type.region,
                         },
                         loc_type.value,
diff --git a/compiler/types/src/types.rs b/compiler/types/src/types.rs
index 95a7d61029..21370aee47 100644
--- a/compiler/types/src/types.rs
+++ b/compiler/types/src/types.rs
@@ -1708,6 +1708,9 @@ pub enum AnnotationSource {
     TypedBody {
         region: Region,
     },
+    RequiredSymbol {
+        region: Region,
+    },
 }
 
 impl AnnotationSource {
@@ -1716,6 +1719,7 @@ impl AnnotationSource {
             &Self::TypedIfBranch { region, .. }
             | &Self::TypedWhenBranch { region, .. }
             | &Self::TypedBody { region, .. } => region,
+            &Self::RequiredSymbol { region, .. } => region,
         }
     }
 }
diff --git a/reporting/src/error/type.rs b/reporting/src/error/type.rs
index 9fbdd6eb2e..a2000ad162 100644
--- a/reporting/src/error/type.rs
+++ b/reporting/src/error/type.rs
@@ -540,12 +540,18 @@ fn to_expr_report<'b>(
                     the_name_text,
                     alloc.text(" definition:"),
                 ]),
+                RequiredSymbol { .. } => alloc.concat([
+                    alloc.text("type annotation of "),
+                    the_name_text,
+                    alloc.text(" required symbol:"),
+                ]),
             };
 
             let it_is = match annotation_source {
                 TypedIfBranch { index, .. } => format!("The {} branch is", index.ordinal()),
                 TypedWhenBranch { index, .. } => format!("The {} branch is", index.ordinal()),
                 TypedBody { .. } => "The body is".into(),
+                RequiredSymbol { .. } => "The provided type is".into(),
             };
 
             let expectation_context = ExpectationContext::Annotation {