cmd/cue/cmd/help.go

// Copyright 2020 CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cmd

import (
	"github.com/spf13/cobra"
)

// TODO: intersperse the examples at the end of the texts in the
// body of text to make things more concerte for the user early on?
// The current approach works will if users just print the text without
// "more" or "less", in which case the examples show more prominently.
// The user can then scroll up to get a more in-depth explanation. But is
// this how users use it?

func newHelpTopics(c *Command) []*cobra.Command {
	return []*cobra.Command{
		inputsHelp,
		flagsHelp,
		filetypeHelp,
	}
}

var inputsHelp = &cobra.Command{
	Use:   "inputs",
	Short: "package list, patterns, and files",
	Long: `Many commands apply to a set of inputs:

cue <command> [inputs]

The list [inputs] may specify CUE packages, CUE files, non-CUE
files or some combinations of those. An empty list specifies
the package in the current directory, provided there is a single
named package in this directory.

CUE packages are specified as an import path. An import path
that is a rooted path --one that begins with a "." or ".."
element-- is interpreted as a file system path and denotes the
package instance in that directory.

Otherwise, the import path P denotes and external package found
in cue.mod/{pkg|gen|usr}/P.

An import path may contain one or more "..." to match any
subdirectory: pkg/... matches all packages below pkg, including
pkg itself, while foo/.../bar matches all directories named bar
within foo. In all cases, directories containing cue.mod
directories are excluded from the result.

A package may also be specified as a list of .cue files.
The special symbol '-' denotes stdin or stdout and defaults to
the cue file type for stdin. For stdout, the default depends on
the cue command. A .cue file package may not be combined with
regular packages.

Non-cue files are interpreted based on their file extension or,
if present, an explicit file qualifier (see the "filetypes"
help topic). Non-cue files may be interpreted as concrete data
or schema. Schema are treated as single-file packages by default.
See the "filetypes" and "flags" help topics on how to combine
schema into a single package.

Data files can be combined into a single package, in which case
each file is unified into a defined location within this single
package. If a data file has multiple values, such as allowed
with JSON Lines or YAML, each value is interpreted as a separate
file.

The --schema/-d flag can be used to unify each data file against
a specific schema within a non-data package. For OpenAPI, the -d
flag specifies a schema name. For JSON Schema the -d flag
specifies a schema defined in "definitions". In all other cases,
the -d flag is a CUE expression that is evaluated within the
package.

Examples (also see also "flags" and "filetypes" help topics):

# Show the definition of each package named foo for each
# directory dir under path.
$ cue def ./path/.../dir:foo

# Unify each document in foo.yaml with the value Foo in pkg.
$ cue export ./pkg -d Foo foo.yaml

# Unify data.json with schema.json.
$ cue export data.json schema: schema.json
`,
}

var flagsHelp = &cobra.Command{
	Use:   "flags",
	Short: "common flags for composing packages",
	Long: `Non-CUE files are treated as individual files by
default, but can be combined into a single package using a
combination of the following flags.


Assigning values to a CUE path

The --path/-l flag can be used to specify a CUE path at which to
place a value. Each -l flag specifies either a CUE expression or
a CUE field (without the value following the colon), both of
which are evaluated within the value. Together, the -l flags
specify the path at increasingly deeper nesting. In the path
notation, path elements that end with a "::", instead of ":",
are created as definitions. An expression may refer to builtin
packages as long as the name can be uniquely identified.

The --with-context flag can be used to evaluate the label
expression within a struct of contextual data, instead of
within the value itself. This struct has the following fields:

{
	// data holds the original source data
	// (perhaps one of several records in a file).
	data: _
	// filename holds the full path to the file.
	filename: string
	// index holds the 0-based index element of the
	// record within the file. For files containing only
	// one record, this will be 0.
	index: uint & <recordCount
	// recordCount holds the total number of records
	// within the file.
	recordCount: int & >=1
}


Handling multiple documents or streams

To handle multi-document files, such as JSON Lines or YAML
files with document separators (---), the user must specify
a the --path, --list, or --files flag.
The --path flag merges each element into a single package as
if each element was defined in a separate file. The --list flag
concatenates each entry in a file into a list.
Using --list flag in combination with the --path flag
concatenates entries with the same path into a list, instead of
unifying them.
Finally, the --files option causes each entry to be written to
a different file. The -files flag may only be used in
combination with the import command.


Examples:

# Put a value at a path based on its "kind" and "name" fields.
$ cue eval -l 'strings.ToLower(kind)' -l name foo.yaml

# Include a schema under the "myschema" field using the path notation.
$ cue eval -l myschema: schema: foo.json

# Base the path values on its kind and file name.
$ cue eval --with-context -l 'path.Base(filename)' -l data.kind foo.yaml
`,
}

var filetypeHelp = &cobra.Command{
	Use:   "filetypes",
	Short: "supported file types and qualifiers",
	Long: `The cue tools supports the following file types:

    Tag         Extensions      Description
    cue         .cue            CUE source files.
    json        .json           JSON files.
    yaml        .yaml/.yml      YAML files.
    jsonl       .jsonl/.ldjson  Line-separated JSON values.
    jsonschema                  JSON Schema.
    openapi                     OpenAPI schema.
    proto        .proto         Protocol Buffer definitions.
    go          .go             Go source files.
    text        .txt            Raw text file; the evaluated
                                value must be of type string.

OpenAPI, JSON Schema and Protocol Buffer definitions are
always interpreted as schema. YAML and JSON are always
interpreted as data. CUE and Go are interpreted as schema by
default, but may be selected to operate in data mode.

The cue tool will infer a file's type from its extension by
default. The user my override this behavior by using qualifiers.
A qualifier takes the form

    <tag>{'+'<tag>}':'

For instance,

	cue eval json: foo.data

specifies that 'foo.data' should be read as a JSON file. File
formats that do not have a default extension may be represented
in any data format using the same notation:

   cue def jsonschema: bar.cue foo.yaml openapi+yaml: baz.def

interprets the files bar.cue and foo.yaml as data in the
respective formats encoding an JSON Schema, while 'baz.def' is
defined to be a YAML file which contents encode OpenAPI
definitions.

A qualifier applies to all files following it on the command line
until the next qualifier. The cue tool does not allow a ':' in
filenames.

The following tags can be used in qualifiers to further
influence input or output. For input these act as
restrictions, validating the input. For output these act
as filters, showing only the requested data and picking
defaults as requested.

    Tag         Description
    data        Require concrete input and output that does
                not require any evaluation.
    graph       Like data, but allow references.
    schema      Export data and definitions.

Many commands also support the --out and --outfile/-o flags.
The --out flag specifies the output type using a qualifier
(without the ':'). The -o flag specifies an output file
possibly prefixed with a qualifier.

Examples:

# Interpret bar.cue and foo.yaml as OpenAPI data.
$ cue def openapi: bar.cue foo.yaml

# Write a CUE package as OpenAPI encoded as YAML, using
# an alternate file extension.
$ cue def -o openapi+yaml:foo.openapi

# Print the data for the current package as YAML.
$ cue export --out=yaml

# Print the string value of the "name" field as a string.
$ cue export -e name --out=text

# Write the string value of the "name" field to a text file.
$ cue export -e name -o=foo.txt

# Write the string value of the "name" field to a file foo.
$ cue export -e name -o=text:foo
`,
}

// TODO: tags
// - doc/nodoc
// - attr/noattr
// - id=<url>

// TODO: filetypes:
// - textpb
// - binpb

// TODO: document
// <tag>['='<value>]{'+'<tag>['='<value>]}':'

// TODO: cue.mod help topic