kube/prototext.libsonnet

// An untyped prototext marshaller. Like std.manifestJson, but when you want to
// emit proto-but-not-really.
//
// This supports recursively nested objects/arrays with string, number and bool
// leaves. All hidden object fields are ignored. The given value must be an
// object.
//
// One unintuitive aspect of proto(text) is that you cannot have
// multidimensional arrays, ie. the following is forbidden:
//
//    manifestProtoText({foo: [[1, 2]]})
//
//    RUNTIME ERROR: manifestProtoText: at .foo[0]: double nested arrays are
//    unsupported by prototext

{
    local top = self,

    // manifestProtoText takes an object and returns a serialized prototext
    // representation of it. If indentation is "", then a single-line prototext
    // will be emitted, otherwise a multi-line prototext will be emitted with
    // each object depth being indented by the indentation value.
    manifestProtoText:: function(value, indentation="  ") top.recurse(value, indentation, 0, [""]),

    // Available as std.repeat in jsonnet 0.15
    repeat:: function(str, count) if count <= 0 then "" else (str + top.repeat(str, count-1)),

    emit:: function(str, indentation, nindent) (
        top.repeat(indentation, nindent) + str + (if indentation == "" then " " else "\n")
    ),

    fatal:: function(str, path) error "manifestProtoText: at %s: %s" % [std.join("", path), str],

    // objectField emits a rendered `k: v` object field, potentially recursing
    // back into recurse for printing the value of object. The value must not
    // be an array, these are handled/flattened by recurse.
    objectField:: function(name, value, indentation, nindent, path) (
        if std.isObject(value) then (
            top.emit("%s <" % [name], indentation, nindent) +
            top.recurse(value, indentation, nindent+1, path) +
            top.emit(">", indentation, nindent)
        ) else if std.isArray(value) then (
            top.fatal("double nested arrays are unsupported by prototext", path)
        ) else if std.isFunction(value) then (
            top.fatal("cannot manifest functions", path)
        ) else if std.isBoolean(value) then (
            top.emit("%s: %s" % [name, if value then "true" else "false"], indentation, nindent)
        ) else if std.isNumber(value) then (
            top.emit("%s: %s" % [name, std.toString(value)], indentation, nindent)
        ) else if std.isString(value) then (
            // Atempt to properly escape strings via JSON manifestation. Not
            // entirely sure this always works.
            top.emit("%s: %s" % [name, std.manifestJson(value)], indentation, nindent)
        ) else (
            top.fatal("unknown type %s" % [std.type(value)], path)
        )
    ),

    // recurse returns the string representation of an object as prototext.
    recurse:: function(value, indentation, nindent, path) (
        if std.isObject(value) then std.join("", [
            (
                local field = value[fieldName];
                if std.isArray(field) then std.join("", std.mapWithIndex(function(i, el) (
                    local newPath = path + ["."+fieldName, "[%d]" % [i]];
                    top.objectField(fieldName, el, indentation, nindent, newPath)
                ), field)) else (
                    local newPath = path + ["."+fieldName];
                    top.objectField(fieldName, field, indentation, nindent, newPath)
                )
            )
            for fieldName in std.objectFields(value)
        ]) else
        top.fatal("manifestProtoText can only manifest objects", path)
    ),
}