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Add a new mangler that allows us to have aliases for dials tags to facilitate migrating from one name to another seamlessly. If both the old name and the new name are set, an error will be returned because the expectation is that you're using one or the other exclusively.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,5 +1,22 @@ | ||
| // Package common provides constants that are used among different dials sources | ||
| package common | ||
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| // DialsTagName is the name of the dials tag. | ||
| const DialsTagName = "dials" | ||
| const ( | ||
| // DialsTagName is the name of the dials tag. | ||
| DialsTagName = "dials" | ||
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| // DialsEnvTagName is the name of the dialsenv tag. | ||
| DialsEnvTagName = "dialsenv" | ||
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| // DialsFlagTagName is the name of the dialsflag tag. | ||
| DialsFlagTagName = "dialsflag" | ||
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| // DialsPFlagTagName is the name of the dialspflag tag. | ||
| DialsPFlagTag = "dialspflag" | ||
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| // DialsFlagAliasTag is the name of the dialsflagalias tag. | ||
| DialsPFlagShortTag = "dialspflagshort" | ||
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| // HelpTextTag is the name of the struct tag for flag descriptions | ||
| DialsHelpTextTag = "dialsdesc" | ||
| ) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,147 @@ | ||
| package transform | ||
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| import ( | ||
| "fmt" | ||
| "reflect" | ||
| "sort" | ||
| "strings" | ||
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| "github.com/fatih/structtag" | ||
| "github.com/vimeo/dials/common" | ||
| ) | ||
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| const ( | ||
| dialsAliasTagSuffix = "alias" | ||
| aliasFieldSuffix = "_alias9wr876rw3" // a random string to append to the alias field to avoid collisions | ||
| ) | ||
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| // AliasMangler manages aliases for dials, dialsenv, dialsflag, and dialspflag | ||
| // struct tags to make it possible to migrate from one name to another | ||
| // conveniently. | ||
| type AliasMangler struct { | ||
| tags []string | ||
| } | ||
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| // NewAliasMangler creates a new AliasMangler with the provided tags. | ||
| func NewAliasMangler(tags ...string) *AliasMangler { | ||
| return &AliasMangler{tags: tags} | ||
| } | ||
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| // Mangle implements the Mangler interface. If any alias tag is defined, the | ||
| // struct field will be copied with the non-aliased tag set to the alias's | ||
| // value. | ||
| func (a *AliasMangler) Mangle(sf reflect.StructField) ([]reflect.StructField, error) { | ||
| originalVals := map[string]string{} | ||
| aliasVals := map[string]string{} | ||
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| sfTags, parseErr := structtag.Parse(string(sf.Tag)) | ||
| if parseErr != nil { | ||
| return nil, fmt.Errorf("error parsing source tags %w", parseErr) | ||
| } | ||
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| anyAliasFound := false | ||
| for _, tag := range a.tags { | ||
| if originalVal, getErr := sfTags.Get(tag); getErr == nil { | ||
| originalVals[tag] = originalVal.Name | ||
| } | ||
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| if aliasVal, getErr := sfTags.Get(tag + dialsAliasTagSuffix); getErr == nil { | ||
| aliasVals[tag] = aliasVal.Name | ||
| anyAliasFound = true | ||
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| // remove the alias tag from the definition | ||
| sfTags.Delete(tag + dialsAliasTagSuffix) | ||
| } | ||
| } | ||
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| if !anyAliasFound { | ||
| // we didn't find any aliases so just get out early | ||
| return []reflect.StructField{sf}, nil | ||
| } | ||
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| aliasField := sf | ||
| aliasField.Name += aliasFieldSuffix | ||
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| // now that we've copied it, reset the struct tags on the source field to | ||
| // not include the alias tags | ||
| sf.Tag = reflect.StructTag(sfTags.String()) | ||
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| tags, parseErr := structtag.Parse(string(aliasField.Tag)) | ||
| if parseErr != nil { | ||
| return nil, fmt.Errorf("error parsing struct tags: %w", parseErr) | ||
| } | ||
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| // keep track of the aliases we actually set so we can update the dialsdesc | ||
| setAliases := []string{} | ||
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| for tag, aliasVal := range aliasVals { | ||
| // remove the alias tag so it's not left on the copied StructField | ||
| tags.Delete(tag + dialsAliasTagSuffix) | ||
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| newDialsTag := &structtag.Tag{ | ||
| Key: tag, | ||
| Name: aliasVal, | ||
| } | ||
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| if setErr := tags.Set(newDialsTag); setErr != nil { | ||
| return nil, fmt.Errorf("error setting new value for dials tag: %w", setErr) | ||
| } | ||
| setAliases = append(setAliases, tag+"="+originalVals[tag]) | ||
| } | ||
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| newDialsDesc := "base dialsdesc unset" // be pessimistic in case dialsdesc isn't set | ||
| if desc, getErr := tags.Get(common.DialsHelpTextTag); getErr == nil { | ||
| newDialsDesc = desc.Name | ||
| } | ||
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| sort.Strings(setAliases) | ||
| newDesc := &structtag.Tag{ | ||
| Key: common.DialsHelpTextTag, | ||
| Name: newDialsDesc + " (alias of " + strings.Join(setAliases, " ") + ")", | ||
| } | ||
| if setErr := tags.Set(newDesc); setErr != nil { | ||
| return nil, fmt.Errorf("error setting amended dialsdesc for tag %w", setErr) | ||
| } | ||
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| // set the new tags on the alias field | ||
| aliasField.Tag = reflect.StructTag(tags.String()) | ||
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| return []reflect.StructField{sf, aliasField}, nil | ||
| } | ||
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| // Unmangle implements the Mangler interface and unwinds the alias copying | ||
| // operation. Note that if both the source and alias are both set in the | ||
| // configuration, an error will be returned. | ||
| func (a *AliasMangler) Unmangle(sf reflect.StructField, fvs []FieldValueTuple) (reflect.Value, error) { | ||
| switch len(fvs) { | ||
| case 1: | ||
| // if there's only one tuple that means there was no alias, so just | ||
| // return... | ||
| return fvs[0].Value, nil | ||
| case 2: | ||
| // two means there's an alias so we should continue on... | ||
| default: | ||
| return reflect.Value{}, fmt.Errorf("expected 1 or 2 tuples, got %d", len(fvs)) | ||
| } | ||
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| if !fvs[0].Value.IsNil() && !fvs[1].Value.IsNil() { | ||
| return reflect.Value{}, fmt.Errorf("both alias and original set for field %q", sf.Name) | ||
| } | ||
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| // return the first one that isn't nil | ||
| for _, fv := range fvs { | ||
| if !fv.Value.IsNil() { | ||
| return fv.Value, nil | ||
| } | ||
| } | ||
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| // if we made it this far, they were both nil, which is fine -- just return | ||
| // one of them. | ||
| return fvs[0].Value, nil | ||
| } | ||
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| // ShouldRecurse is called after Mangle for each field so nested struct | ||
| // fields get iterated over after any transformation done by Mangle(). | ||
| func (a AliasMangler) ShouldRecurse(_ reflect.StructField) bool { | ||
| return true | ||
| } |
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