• Rob Pike's avatar
    fmt: print maps in key-sorted order · a440cc0d
    Rob Pike authored
    For easier testing, change the way maps are printed so they
    appear in a consistent order between runs. Do this by printing
    them in key-sorted order.
    
    To do this, we add a package at the root, internal/fmtsort,
    that implements a general mechanism for sorting map keys
    regardless of their type. This is a little messy and probably
    slow, but formatted printing of maps has never been fast and
    is already always reflection-driven.
    
    The rules are:
    
    The ordering rules are more general than with Go's < operator:
    
     - when applicable, nil compares low
     - ints, floats, and strings order by <
     - NaN compares less than non-NaN floats
     - bool compares false before true
     - complex compares real, then imag
     - pointers compare by machine address
     - channel values compare by machine address
     - structs compare each field in turn
     - arrays compare each element in turn.
     - interface values compare first by reflect.Type describing the concrete type
       and then by concrete value as described in the previous rules.
    
    The new package is internal because we really do not want
    everyone using this to sort things. It is slow, not general, and
    only suitable for the subset of types that can be map keys.
    
    Also use the package in text/template, which already had a
    weaker version of this mechanism.
    
    This change requires adding a dependency on sort to the fmt
    package, but that isn't disruptive to the dependency tree.
    
    Fixes #21095
    
    Change-Id: Ia602115c7de5d95993dbd609611d8bd96e054157
    Reviewed-on: https://go-review.googlesource.com/c/142737Reviewed-by: 's avatarBrad Fitzpatrick <bradfitz@golang.org>
    Reviewed-by: 's avatarRuss Cox <rsc@golang.org>
    a440cc0d
sort_test.go 5.15 KB