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Support Description() on subcommands #167

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Support Description() on subcommands #167

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10 changes: 9 additions & 1 deletion usage.go
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Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,15 @@ func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
}
}

if p.description != "" {
var description string
if v := p.val(cmd.dest); v.IsValid() && !isZero(v) {
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I don't think it makes sense to include !isZero(v) in here because v.IsValid already checks that (see https://cs.opensource.google/go/go/+/refs/tags/go1.17.5:src/reflect/value.go;l=1435)

The basic issue with this approach is that it won't work if the struct for this subcommand has a parent that is nil, since in that case we will end up here and then v.IsValid() will return true.

It would be better to store the type for each subcommand in the command struct and then instantiate a new struct of that type right here and check whether it satisfies the Described interface

if d, ok := v.Interface().(Described); ok {
description = d.Description()
}
}
if description != "" {
fmt.Fprintln(w, description)
} else if p.description != "" {
fmt.Fprintln(w, p.description)
}
p.writeUsageForSubcommand(w, cmd)
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2 changes: 2 additions & 0 deletions usage_test.go
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Expand Up @@ -317,6 +317,7 @@ func TestUsageWithNestedSubcommands(t *testing.T) {
expectedUsage := "Usage: example child nested [--enable] OUTPUT"

expectedHelp := `
this program does this and that
Usage: example child nested [--enable] OUTPUT

Positional arguments:
Expand All @@ -336,6 +337,7 @@ Global options:
Child *struct {
Values []float64 `help:"Values"`
Nested *struct {
described
Enable bool
Output string `arg:"positional,required"`
} `arg:"subcommand:nested"`
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