fix(gnovm): annotate specific reason a value does not implement an in…

…terface (gnolang#2492)

Related to gnolang#1684 .
This is a first draft that will increment the amount of information Gno
returns in the case of an struct not implementing a defined interface.

### First Case
`A non defined function on interface`
```go
package main

type Car interface{
	Run(speed int)
}

type Toyota struct {}
func main(){
	var car Car = &Toyota{}
}
```
**Before** we had something like:
`panic: *main.Toyota does not implement main.Car [recovered]`
**now**:
`panic: *main.Toyota does not implement main.Car (missing method Run)
[recovered]`

### Second Case
`A defined function with bad type on function signature`
```go
package main

type Car interface{
	Run(speed int)
}

type Toyota struct {}

func (toyota *Toyota) Run(quick bool){
}

func main(){
	var car Car = &Toyota{}
}
```
**Before** we had something like:
`panic: *main.Toyota does not implement main.Car [recovered]`
**now**:
`panic: *main.Toyota does not implement main.Car (wrong type for method
Run) [recovered]`

### Third Case
`A defined function with a pointer receiver but not pointer variable`
```go
package main

type Car interface {
	Run()
}

type Toyota struct {
}

func (t *Toyota) Run() {

}

func main() {
	var car Car = Toyota{}
}
```
**Before** we had something like:
`panic: *main.Toyota does not implement main.Car [recovered]`
**now**:
`panic: main.Toyota does not implement main.Car (method Run has pointer
receiver):`

<!-- please provide a detailed description of the changes made in this
pull request. -->

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gnovm/pkg/gnolang/op_expressions.go

@@ -238,14 +238,14 @@ func (m *Machine) doOpTypeAssert1() {
 
 			// t is Gno interface.
 			// assert that x implements type.
-			var impl bool
-			impl = it.IsImplementedBy(xt)
-			if !impl {
+			err := it.VerifyImplementedBy(xt)
+			if err != nil {
 				// TODO: default panic type?
 				ex := fmt.Sprintf(
-					"%s doesn't implement %s",
+					"%s doesn't implement %s (%s)",
 					xt.String(),
-					it.String())
+					it.String(),
+					err.Error())
 				m.Panic(typedString(ex))
 				return
 			}

gnovm/pkg/gnolang/type_check.go

@@ -237,14 +237,15 @@ func checkAssignableTo(xt, dt Type, autoNative bool) error {
 			if idt.IsEmptyInterface() { // XXX, can this be merged with IsImplementedBy?
 				// if dt is an empty Gno interface, any x ok.
 				return nil // ok
-			} else if idt.IsImplementedBy(xt) {
+			} else if err := idt.VerifyImplementedBy(xt); err == nil {
 				// if dt implements idt, ok.
 				return nil // ok
 			} else {
 				return errors.New(
-					"%s does not implement %s",
+					"%s does not implement %s (%s)",
 					xt.String(),
-					dt.String())
+					dt.String(),
+					err.Error())
 			}
 		} else if ndt, ok := baseOf(dt).(*NativeType); ok {
 			nidt := ndt.Type

gnovm/pkg/gnolang/types.go

@@ -1009,21 +1009,21 @@ func (it *InterfaceType) FindEmbeddedFieldType(callerPath string, n Name, m map[
 
 // For run-time type assertion.
 // TODO: optimize somehow.
-func (it *InterfaceType) IsImplementedBy(ot Type) (result bool) {
+func (it *InterfaceType) VerifyImplementedBy(ot Type) error {
 	for _, im := range it.Methods {
 		if im.Type.Kind() == InterfaceKind {
 			// field is embedded interface...
 			im2 := baseOf(im.Type).(*InterfaceType)
-			if !im2.IsImplementedBy(ot) {
-				return false
+			if err := im2.VerifyImplementedBy(ot); err != nil {
+				return err
 			} else {
 				continue
 			}
 		}
 		// find method in field.
 		tr, hp, rt, ft, _ := findEmbeddedFieldType(it.PkgPath, ot, im.Name, nil)
 		if tr == nil { // not found.
-			return false
+			return fmt.Errorf("missing method %s", im.Name)
 		}
 		if nft, ok := ft.(*NativeType); ok {
 			// Treat native function types as autoNative calls.
@@ -1033,22 +1033,26 @@ func (it *InterfaceType) IsImplementedBy(ot Type) (result bool) {
 			// ie, if each of ft's arg types can match
 			// against the desired arg types in im.Types.
 			if !gno2GoTypeMatches(im.Type, nft.Type) {
-				return false
+				return fmt.Errorf("wrong type for method %s", im.Name)
 			}
 		} else if mt, ok := ft.(*FuncType); ok {
 			// if method is pointer receiver, check addressability:
 			if _, ptrRcvr := rt.(*PointerType); ptrRcvr && !hp {
-				return false // not addressable.
+				return fmt.Errorf("method %s has pointer receiver", im.Name) // not addressable.
 			}
 			// check for func type equality.
 			dmtid := mt.TypeID()
 			imtid := im.Type.TypeID()
 			if dmtid != imtid {
-				return false
+				return fmt.Errorf("wrong type for method %s", im.Name)
 			}
 		}
 	}
-	return true
+	return nil
+}
+
+func (it *InterfaceType) IsImplementedBy(ot Type) bool {
+	return it.VerifyImplementedBy(ot) == nil
 }
 
 func (it *InterfaceType) GetPathForName(n Name) ValuePath {

gnovm/tests/files/access6_stdlibs.gno

@@ -16,4 +16,4 @@ func main() {
 }
 
 // Error:
-// main/files/access6_stdlibs.gno:15:2: main.mystruct does not implement gno.land/p/demo/testutils.PrivateInterface
+// main/files/access6_stdlibs.gno:15:2: main.mystruct does not implement gno.land/p/demo/testutils.PrivateInterface (missing method privateMethod)

gnovm/tests/files/access7_stdlibs.gno

@@ -20,4 +20,4 @@ func main() {
 }
 
 // Error:
-// main/files/access7_stdlibs.gno:19:2: main.PrivateInterface2 does not implement gno.land/p/demo/testutils.PrivateInterface
+// main/files/access7_stdlibs.gno:19:2: main.PrivateInterface2 does not implement gno.land/p/demo/testutils.PrivateInterface (missing method privateMethod)

gnovm/tests/files/fun27.gno

@@ -13,4 +13,4 @@ func main() {
 }
 
 // Error:
-// main/files/fun27.gno:8:2: <untyped> bigint does not implement main.Foo
+// main/files/fun27.gno:8:2: <untyped> bigint does not implement main.Foo (missing method foo)

gnovm/tests/files/type24b.gno

@@ -46,4 +46,4 @@ func assertValue() {
 // Output:
 // int is not of type string
 // interface{} is not of type string
-// *github.com/gnolang/gno/_test/net/http/httptest.ResponseRecorder doesn't implement interface{Push func(string;*github.com/gnolang/gno/_test/net/http.PushOptions)(.uverse.error)}
+// *github.com/gnolang/gno/_test/net/http/httptest.ResponseRecorder doesn't implement interface{Push func(string;*github.com/gnolang/gno/_test/net/http.PushOptions)(.uverse.error)} (missing method Push)

gnovm/tests/files/typeassert4a.gno

@@ -58,5 +58,5 @@ func main() {
 // interface conversion: interface is nil, not main.Setter
 // interface conversion: interface is nil, not main.Setter
 // ok
-// main.ValueSetter doesn't implement interface{Set func(string)()}
+// main.ValueSetter doesn't implement interface{Set func(string)()} (method Set has pointer receiver)
 // ok

gnovm/tests/files/typeassert6a.gno

@@ -36,5 +36,5 @@ func main() {
 }
 
 // Output:
-// int doesn't implement interface{Do func(string)()}
-// *int doesn't implement interface{Do func(string)()}
+// int doesn't implement interface{Do func(string)()} (missing method Do)
+// *int doesn't implement interface{Do func(string)()} (missing method Do)

gnovm/tests/files/typeassert9a.gno

@@ -0,0 +1,19 @@
+package main
+
+// First interface
+type Reader interface {
+	Read(int) string
+}
+
+type csvReader struct{}
+func (r*csvReader) Read(string) string{
+	return ""
+}
+
+
+func main() {
+	var csvReader Reader = &csvReader{}
+}
+
+// Error:
+// main/files/typeassert9a.gno:15:6: *main.csvReader does not implement main.Reader (wrong type for method Read)

gnovm/tests/files/types/assign_type_assertion_c.gno

@@ -30,4 +30,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/assign_type_assertion_c.gno:23:2: interface{IsSet func()(bool)} does not implement interface{IsNotSet func()(bool)}
+// main/files/types/assign_type_assertion_c.gno:23:2: interface{IsSet func()(bool)} does not implement interface{IsNotSet func()(bool)} (missing method IsNotSet)

gnovm/tests/files/types/eql_0b4_stdlibs.gno

@@ -10,4 +10,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/eql_0b4_stdlibs.gno:9:10: <untyped> bigint does not implement .uverse.error
+// main/files/types/eql_0b4_stdlibs.gno:9:10: <untyped> bigint does not implement .uverse.error (missing method Error)

gnovm/tests/files/types/eql_0f0_stdlibs.gno

@@ -25,4 +25,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/eql_0f0_stdlibs.gno:19:5: <untyped> bigint does not implement .uverse.error
+// main/files/types/eql_0f0_stdlibs.gno:19:5: <untyped> bigint does not implement .uverse.error (missing method Error)

gnovm/tests/files/types/eql_0f1_stdlibs.gno

@@ -25,4 +25,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/eql_0f1_stdlibs.gno:19:5: int64 does not implement .uverse.error
+// main/files/types/eql_0f1_stdlibs.gno:19:5: int64 does not implement .uverse.error (missing method Error)

gnovm/tests/files/types/eql_0f41_stdlibs.gno

@@ -32,4 +32,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/eql_0f41_stdlibs.gno:27:5: main.animal does not implement .uverse.error
+// main/files/types/eql_0f41_stdlibs.gno:27:5: main.animal does not implement .uverse.error (missing method Error)

gnovm/tests/files/types/eql_0f8_stdlibs.gno

@@ -24,4 +24,4 @@ func main() {
 }
 
 // Error:
-// main/files/types/eql_0f8_stdlibs.gno:19:5: int64 does not implement .uverse.error
+// main/files/types/eql_0f8_stdlibs.gno:19:5: int64 does not implement .uverse.error (missing method Error)