rpcbinding: check duplicating struct fields before binding generation

RPC binding config may be malformed or the source .go contract may contain
structures like this:
```
type Str struct {
    Field int
    field int
}
```
We need to recognise these cases and return error. otherwise the resulting
binding can't be compiled.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

cli/smartcontract/generate_test.go

@@ -562,3 +562,51 @@ func TestCompile_GuessEventTypes(t *testing.T) {
 		check(t, filepath.Join("testdata", "rpcbindings", "invalid5"), "configured declared named type intersects with the contract's one: `invalid5.NamedStruct`")
 	})
 }
+
+func TestGenerateRPCBindings_Errors(t *testing.T) {
+	app := cli.NewApp()
+	app.Commands = NewCommands()
+	app.ExitErrHandler = func(*cli.Context, error) {}
+
+	t.Run("duplicating resulting fields", func(t *testing.T) {
+		check := func(t *testing.T, packageName string, autogen bool, expectedError string) {
+			tmpDir := t.TempDir()
+			source := filepath.Join("testdata", "rpcbindings", packageName)
+			configFile := filepath.Join(source, "invalid.yml")
+			out := filepath.Join(tmpDir, "rpcbindings.out")
+			manifestF := filepath.Join(tmpDir, "manifest.json")
+			bindingF := filepath.Join(tmpDir, "binding.yml")
+			nefF := filepath.Join(tmpDir, "out.nef")
+			cmd := []string{"", "contract", "compile",
+				"--in", source,
+				"--config", configFile,
+				"--manifest", manifestF,
+				"--bindings", bindingF,
+				"--out", nefF,
+			}
+			if autogen {
+				cmd = append(cmd, "--guess-eventtypes")
+			}
+			require.NoError(t, app.Run(cmd))
+
+			cmds := []string{"", "contract", "generate-rpcwrapper",
+				"--config", bindingF,
+				"--manifest", manifestF,
+				"--out", out,
+			}
+			err := app.Run(cmds)
+			require.Error(t, err)
+			require.True(t, strings.Contains(err.Error(), expectedError), err.Error())
+		}
+
+		t.Run("event", func(t *testing.T) {
+			check(t, "invalid6", false, "error during generation: named type `SomeStruct` has two fields with identical resulting binding name `Field`")
+		})
+		t.Run("autogen event", func(t *testing.T) {
+			check(t, "invalid7", true, "error during generation: named type `invalid7.SomeStruct` has two fields with identical resulting binding name `Field`")
+		})
+		t.Run("struct", func(t *testing.T) {
+			check(t, "invalid8", false, "error during generation: named type `invalid8.SomeStruct` has two fields with identical resulting binding name `Field`")
+		})
+	})
+}

cli/smartcontract/testdata/rpcbindings/invalid6/invalid.go

@@ -0,0 +1,14 @@
+package invalid6
+
+import "github.com/nspcc-dev/neo-go/pkg/interop/runtime"
+
+type SomeStruct struct {
+	Field int
+	// RPC binding generator will convert this field into exported, which matches
+	// exactly the existing Field.
+	field int
+}
+
+func Main() {
+	runtime.Notify("SomeEvent", SomeStruct{Field: 123, field: 123})
+}

cli/smartcontract/testdata/rpcbindings/invalid6/invalid.yml

@@ -0,0 +1,18 @@
+name: Test duplicating event fields
+events:
+  - name: SomeEvent
+    parameters:
+      - name: p1
+        type: Struct
+        extendedtype:
+          base: Struct
+          name: SomeStruct
+namedtypes:
+  SomeStruct:
+    base: Struct
+    name: SomeStruct
+    fields:
+      - field: Field
+        base: Integer
+      - field: field
+        base: Integer

cli/smartcontract/testdata/rpcbindings/invalid7/invalid.go

@@ -0,0 +1,14 @@
+package invalid7
+
+import "github.com/nspcc-dev/neo-go/pkg/interop/runtime"
+
+type SomeStruct struct {
+	Field int
+	// RPC binding generator will convert this field into exported, which matches
+	// exactly the existing Field.
+	field int
+}
+
+func Main() {
+	runtime.Notify("SomeEvent", SomeStruct{Field: 123, field: 123})
+}

cli/smartcontract/testdata/rpcbindings/invalid7/invalid.yml

@@ -0,0 +1,6 @@
+name: Test duplicating autogenerated event fields
+events:
+  - name: SomeEvent
+    parameters:
+      - name: p1
+        type: Struct

cli/smartcontract/testdata/rpcbindings/invalid8/invalid.go

@@ -0,0 +1,16 @@
+package invalid8
+
+type SomeStruct struct {
+	Field int
+	// RPC binding generator will convert this field into exported, which matches
+	// exactly the existing Field.
+	field int
+}
+
+func Main() SomeStruct {
+	s := SomeStruct{
+		Field: 1,
+		field: 2,
+	}
+	return s
+}

cli/smartcontract/testdata/rpcbindings/invalid8/invalid.yml

@@ -0,0 +1 @@
+name: Test duplicating struct fields

pkg/smartcontract/rpcbinding/binding.go

@@ -430,6 +430,28 @@ func Generate(cfg binding.Config) error {
 	ctr = scTemplateToRPC(cfg, ctr, imports, scTypeToGo)
 	ctr.NamedTypes = cfg.NamedTypes
 
+	// Check resulting named types and events don't have duplicating field names.
+	for _, t := range ctr.NamedTypes {
+		fDict := make(map[string]struct{})
+		for _, n := range t.Fields {
+			name := upperFirst(n.Field)
+			if _, ok := fDict[name]; ok {
+				return fmt.Errorf("named type `%s` has two fields with identical resulting binding name `%s`", t.Name, name)
+			}
+			fDict[name] = struct{}{}
+		}
+	}
+	for _, e := range ctr.CustomEvents {
+		fDict := make(map[string]struct{})
+		for _, n := range e.Parameters {
+			name := upperFirst(n.Name)
+			if _, ok := fDict[name]; ok {
+				return fmt.Errorf("event `%s` has two fields with identical resulting binding name `%s`", e.Name, name)
+			}
+			fDict[name] = struct{}{}
+		}
+	}
+
 	var srcTemplate = template.Must(template.New("generate").Funcs(template.FuncMap{
 		"addIndent":       addIndent,
 		"etTypeConverter": etTypeConverter,