Add support for changed types in thriftbreak (#559)

* Add check for changed types

* Update error message

* Update struct name

internal/compare/compare.go

@@ -99,6 +99,22 @@ func (p *Pass) requiredField(fromField, toField *compile.FieldSpec, to *compile.
 	}
 }
 
+func (p *Pass) changedTypes(fromField, toField *compile.FieldSpec, to *compile.StructSpec, file string) {
+	if fromField.Type == nil || toField.Type == nil {
+		return
+	}
+
+	if fromField.Type.ThriftName() != toField.Type.ThriftName() {
+		p.Report(Diagnostic{
+			FilePath: file,
+			Message: fmt.Sprintf(
+				"changing type of field %q in struct %q from %q to %q",
+				toField.ThriftName(), to.ThriftName(), fromField.Type.ThriftName(),
+				toField.Type.ThriftName()),
+		})
+	}
+}
+
 // StructSpecs compares two structs defined in a Thrift file.
 func (p *Pass) structSpecs(from, to *compile.StructSpec, file string) {
 	fields := make(map[int16]*compile.FieldSpec, len(from.Fields))
@@ -109,6 +125,7 @@ func (p *Pass) structSpecs(from, to *compile.StructSpec, file string) {
 	for _, toField := range to.Fields {
 		if fromField, ok := fields[toField.ID]; ok {
 			p.requiredField(fromField, toField, to, file)
+			p.changedTypes(fromField, toField, to, file)
 		} else if toField.Required {
 			p.Report(Diagnostic{
 				FilePath: file,

internal/compare/compare_test.go

@@ -101,6 +101,32 @@ func TestErrorRequiredCase(t *testing.T) {
 			wantError: `foo.thrift:changing an optional field "fieldA" in "structA" to required` +
 				"\n" + `foo.thrift:changing an optional field "fieldB" in "structA" to required`,
 		},
+		{
+			desc: "found a type changed",
+			fromStruct: &compile.StructSpec{
+				Name: "structA",
+				Fields: compile.FieldGroup{
+					&compile.FieldSpec{
+						Name: "fieldA",
+						Type: &compile.BinarySpec{},
+					},
+				},
+			},
+			toStruct: &compile.StructSpec{
+				Name: "structA",
+				Fields: compile.FieldGroup{
+					&compile.FieldSpec{
+						Name: "fieldA",
+						Type: &compile.BoolSpec{},
+					},
+					&compile.FieldSpec{
+						Name: "fieldB",
+						Type: &compile.BinarySpec{},
+					},
+				},
+			},
+			wantError: `foo.thrift:changing type of field "fieldA" in struct "structA" from "binary" to "bool"`,
+		},
 	}
 
 	for _, tt := range tests {