John Boiles created THRIFT-4868:
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Summary: Go bug for sets with a default value
Key: THRIFT-4868
URL: https://issues.apache.org/jira/browse/THRIFT-4868
Project: Thrift
Issue Type: Task
Components: Go - Compiler
Affects Versions: 0.12.0
Reporter: John Boiles
There's a bug in the Thrift Go generator that happens when set types are used
with a default field. For example, a simple struct like this:
{code:java}
struct SetPointerTest {
1: optional set<string> with_default = [ "test" ]
}
{code}
Generates a struct like this
{code}
type SetPointerTest struct {
WithDefault *[]string `thrift:"with_default,1" db:"with_default"
json:"with_default"`
}
{code}
And associated Go code with a line like this:
{code:go}
if reflect.DeepEqual(*p.WithDefault[i],*p.WithDefault[j]) {
{code}
Which fails with an error
{code}
gen-go/setpointertest/SetPointerTest.go:125:44: invalid operation:
p.WithDefault[i] (type *[]string does not support indexing)
{code}
Thrift sets only get translated to Go pointer values (causing this error) when
a default value is set. This is because the
{{t_go_generator::is_pointer_field}} method has [some
logic|https://github.com/apache/thrift/blob/master/compiler/cpp/src/thrift/generate/t_go_generator.cc#L410-L411]
that returns {{true}} if the set has a default value. I'm unsure why this is
the case; it seems simpler to not change the type when there's a default value.
A Golang slice is a pointer value by default, so {{nil}} can still be used for
{{optional}} fields. I'd be super interested to understand why the code was
written this way.
However, since changing the pointer behavior would be a version-incompatible
change, I propose we do the simple thing for now to fix Go compilation. I'll
submit a patch with a test shortly.
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