Specific info message for equally named effect operations (#956)

## Enhance  Reporting for Missing `do` Syntax in Effect Operations  

This pull request improves error messages for unresolved function calls
in the presence of equally named effect operations, addressing issue
[#950](#950).

---

## Summary  
This update enhances the info message in the `Namer` component of Effekt
when an equally named effect operation exists but has not been invoked
using the `do` syntax. It ensures the user is provided with a more
descriptive information message, avoiding the generic `"Cannot find a
function named _"`.

---

## Changes  
### 1. **Improved Information in `Namer.scala`**:
- Removed `lookupOverloaded` and with it the never issued information on
fields and added `lookupOperation` to capture equally named effect
operations the `resolveFunctionCallTarget` method.
- When an equally named effect operation is found, an **information
message** is provided to the user with the recommended syntax (`do
{operationName}()`).
   
### 3. **Added Negative Tests**:
- Introduced three new tests in `examples/neg/namer/issue950` to verify
the following cases:
- An info message is displayed when an effect operation is invoked
without the `do` syntax.
- The generic message is displayed when no valid function or operation
matches the call.
     - Overloaded Effects all get captured by the `foreach`

---


## Example Behavior  

### Before the Fix  
```scala
interface Greet { def sayHello(): Unit }

def helloWorld() = try {
  sayHello()
  // [error] Cannot find a function named `sayHello`.
} with Greet {
  def sayHello() = { println("Hello!"); resume(()) }
}

def main() = {
  helloWorld() // Generic error, not helpful
}
```

### After the Fix  
```scala
interface Greet { def sayHello(): Unit }

def helloWorld() = try {
  sayHello()
  // [error] There is an equally named effect operation `sayHello` of interface `Greet`. Use syntax `do sayHello()` to call it.
} with Greet {
  def sayHello() = { println("Hello!"); resume(()) }
}

def main() = {
  helloWorld() // Specific error with actionable advice
}
```

---

## Testing  
- **Negative Test 1**: Missing `do` for effect operation:
- Confirms that invoking an effect operation without the `do` syntax
triggers the improved error message.
- **Negative Test 2**: Unresolved function call:
- Ensures that the generic error message appears when no matches
(operations, fields, or overloads) are found.
- **Negative Test 3**: Overloaded effect operations:
- Confirms that overloaded effect operations are all captured by the new
foreach

---------

Co-authored-by: Jiří Beneš <[email protected]>

Author: JakubSchwenkbeck

effekt/shared/src/main/scala/effekt/Namer.scala

@@ -921,14 +921,14 @@ trait NamerOps extends ContextOps { Context: Context =>
         assignSymbol(id, value)
       case Right(blocks) =>
         if (blocks.isEmpty) {
-          val allSyms = scope.lookupOverloaded(id, term => true).flatten
+          val ops = scope.lookupOperation(id.path, id.name).flatten
 
-          if (allSyms.exists { case o: Operation => true; case _ => false })
-            info(pretty"There is an equally named effect operation. Use syntax `do ${id}() to call it.`")
-
-          if (allSyms.exists { case o: Field => true; case _ => false })
-            info(pretty"There is an equally named field. Use syntax `obj.${id} to access it.`")
+          // Provide specific info messages for operations
+          ops.foreach { op =>
+            info(pretty"There is an equally named effect operation ${op} of interface ${op.interface}. Use syntax `do ${id}()` to call it.")
+          }
 
+          // Always abort with the generic message
           abort(pretty"Cannot find a function named `${id}`.")
         }
         assignSymbol(id, CallTarget(blocks))

examples/neg/namer/issue950/ambiguous_interfaces_overload.check

@@ -0,0 +1,9 @@
+[info] examples/neg/namer/issue950/ambiguous_interfaces_overload.effekt:5:3: There is an equally named effect operation sayHello of interface Greet. Use syntax `do sayHello()` to call it.
+  sayHello() 
+  ^^^^^^^^
+[info] examples/neg/namer/issue950/ambiguous_interfaces_overload.effekt:5:3: There is an equally named effect operation sayHello of interface Welcome. Use syntax `do sayHello()` to call it.
+  sayHello() 
+  ^^^^^^^^
+[error] examples/neg/namer/issue950/ambiguous_interfaces_overload.effekt:5:3: Cannot find a function named `sayHello`.
+  sayHello() 
+  ^^^^^^^^

examples/neg/namer/issue950/ambiguous_interfaces_overload.effekt

@@ -0,0 +1,12 @@
+interface Greet { def sayHello(): Unit }
+interface Welcome { def sayHello(): Unit }
+
+def helloWorld() = try {
+  sayHello() 
+} with Greet {
+  def sayHello() = { println("Hello from Greet!"); resume(()) }
+}
+
+def main() = {
+  helloWorld() 
+}

examples/neg/namer/issue950/cannot_find_function.effekt

@@ -0,0 +1 @@
+def main() = doesNotExist() // ERROR Cannot find a function named `doesNotExist`.

examples/neg/namer/issue950/effect_operation_with_same_name.check

@@ -0,0 +1,6 @@
+[info] examples/neg/namer/issue950/effect_operation_with_same_name.effekt:4:3: There is an equally named effect operation sayHello of interface Greet. Use syntax `do sayHello()` to call it.
+  sayHello()
+  ^^^^^^^^
+[error] examples/neg/namer/issue950/effect_operation_with_same_name.effekt:4:3: Cannot find a function named `sayHello`.
+  sayHello()
+  ^^^^^^^^

examples/neg/namer/issue950/effect_operation_with_same_name.effekt

@@ -0,0 +1,11 @@
+interface Greet { def sayHello(): Unit }
+
+def helloWorld() = try {
+  sayHello()
+} with Greet {
+  def sayHello() = { println("Hello!"); resume(()) }
+}
+
+def main() = {
+  helloWorld()
+}