• Daniel Martí's avatar
    text/template: differentiate nil from missing arg · 3cb54c86
    Daniel Martí authored
    reflect.Value is a struct and does not have a kind nor any flag for
    untyped nils. As a result, it is tricky to differentiate when we're
    missing a value, from when we have one but it is untyped nil.
    
    We could start using *reflect.Value instead, to add one level of
    indirection, using nil for missing values and new(reflect.Value) for
    untyped nils. However, that is a fairly invasive change, and would also
    mean unnecessary allocations.
    
    Instead, use a special reflect.Value that depicts when a value is
    missing. This is the case for the "final" reflect.Value in multiple
    scenarios, such as the start of a pipeline. Give it a specific,
    unexported type too, to make sure it cannot be mistaken for any other
    valid value.
    
    Finally, replace "final.IsValid()" with "final != missingVal", since
    final.IsValid() will be false when final is an untyped nil.
    
    Also add a few test cases, all different variants of the untyped nil
    versus missing value scenario.
    
    Fixes #18716.
    
    Change-Id: Ia9257a84660ead5a7007fd1cced7782760b62d9d
    Reviewed-on: https://go-review.googlesource.com/95215
    Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarRob Pike <r@golang.org>
    3cb54c86
exec_test.go 44.9 KB