GODRIVER-1729 Fix vet and fmt errors for Go 1.15

- go vet disallows string(int) conversions, which the driver uses to
append null terminators in bsoncore. This commit switches those
conversions from string(0) to string(byte(0)).

- gofmt fails if a function's body is on the same line as it's
declarations so such functions have been changed to span multiple lines.

Author: Divjot Arora

bson/bson_test.go

@@ -30,7 +30,9 @@ func noerr(t *testing.T, err error) {
 	}
 }
 
-func requireErrEqual(t *testing.T, err1 error, err2 error) { require.True(t, compareErrors(err1, err2)) }
+func requireErrEqual(t *testing.T, err1 error, err2 error) {
+	require.True(t, compareErrors(err1, err2))
+}
 
 func TestTimeRoundTrip(t *testing.T) {
 	val := struct {

bson/raw_value.go

@@ -104,7 +104,9 @@ func (rv RawValue) UnmarshalWithContext(dc *bsoncodec.DecodeContext, val interfa
 }
 
 func convertFromCoreValue(v bsoncore.Value) RawValue { return RawValue{Type: v.Type, Value: v.Data} }
-func convertToCoreValue(v RawValue) bsoncore.Value   { return bsoncore.Value{Type: v.Type, Data: v.Value} }
+func convertToCoreValue(v RawValue) bsoncore.Value {
+	return bsoncore.Value{Type: v.Type, Data: v.Value}
+}
 
 // Validate ensures the value is a valid BSON value.
 func (rv RawValue) Validate() error { return convertToCoreValue(rv).Validate() }
@@ -176,7 +178,9 @@ func (rv RawValue) ObjectID() primitive.ObjectID { return convertToCoreValue(rv)
 
 // ObjectIDOK is the same as ObjectID, except it returns a boolean instead of
 // panicking.
-func (rv RawValue) ObjectIDOK() (primitive.ObjectID, bool) { return convertToCoreValue(rv).ObjectIDOK() }
+func (rv RawValue) ObjectIDOK() (primitive.ObjectID, bool) {
+	return convertToCoreValue(rv).ObjectIDOK()
+}
 
 // Boolean returns the boolean value the Value represents. It panics if the
 // value is a BSON type other than boolean.
@@ -214,7 +218,9 @@ func (rv RawValue) RegexOK() (pattern, options string, ok bool) {
 
 // DBPointer returns the BSON dbpointer value the Value represents. It panics if the value is a BSON
 // type other than DBPointer.
-func (rv RawValue) DBPointer() (string, primitive.ObjectID) { return convertToCoreValue(rv).DBPointer() }
+func (rv RawValue) DBPointer() (string, primitive.ObjectID) {
+	return convertToCoreValue(rv).DBPointer()
+}
 
 // DBPointerOK is the same as DBPoitner, except that it returns a boolean
 // instead of panicking.

mongo/mongo_test.go

@@ -116,7 +116,7 @@ func TestMongoHelpers(t *testing.T) {
 			got, id, err := transformAndEnsureID(bson.DefaultRegistry, doc)
 			assert.Nil(t, err, "transformAndEnsureID error: %v", err)
 			_, ok := id.(string)
-			assert.True(t, ok, "expected returned id type %T, got %T", string(0), id)
+			assert.True(t, ok, "expected returned id type string, got %T", id)
 			assert.Equal(t, got, want, "expected document %v, got %v", got, want)
 		})
 	})

x/bsonx/bsoncore/bsoncore.go

@@ -39,11 +39,14 @@ import (
 // EmptyDocumentLength is the length of a document that has been started/ended but has no elements.
 const EmptyDocumentLength = 5
 
+// nullTerminator is a string version of the 0 byte that is appended at the end of cstrings.
+const nullTerminator = string(byte(0))
+
 // AppendType will append t to dst and return the extended buffer.
 func AppendType(dst []byte, t bsontype.Type) []byte { return append(dst, byte(t)) }
 
 // AppendKey will append key to dst and return the extended buffer.
-func AppendKey(dst []byte, key string) []byte { return append(dst, key+string(0x00)...) }
+func AppendKey(dst []byte, key string) []byte { return append(dst, key+nullTerminator...) }
 
 // AppendHeader will append Type t and key to dst and return the extended
 // buffer.
@@ -427,7 +430,7 @@ func AppendNullElement(dst []byte, key string) []byte { return AppendHeader(dst,
 
 // AppendRegex will append pattern and options to dst and return the extended buffer.
 func AppendRegex(dst []byte, pattern, options string) []byte {
-	return append(dst, pattern+string(0x00)+options+string(0x00)...)
+	return append(dst, pattern+nullTerminator+options+nullTerminator...)
 }
 
 // AppendRegexElement will append a BSON regex element using key, pattern, and

x/mongo/driver/wiremessage/wiremessage.go

@@ -490,7 +490,9 @@ func ReadCompressedOriginalOpCode(src []byte) (opcode OpCode, rem []byte, ok boo
 
 // ReadCompressedUncompressedSize reads the uncompressed size of a
 // compressed wiremessage to dst.
-func ReadCompressedUncompressedSize(src []byte) (size int32, rem []byte, ok bool) { return readi32(src) }
+func ReadCompressedUncompressedSize(src []byte) (size int32, rem []byte, ok bool) {
+	return readi32(src)
+}
 
 // ReadCompressedCompressorID reads the ID of the compressor to dst.
 func ReadCompressedCompressorID(src []byte) (id CompressorID, rem []byte, ok bool) {