Output format: json

The json output format is intended to be used as a machine-readable output, to be interpreted by tooling, although humans may also use it, as it provides the most detailed output of all supported output formats.

As described on the output-formats page, cargo-msrv reports the status of the program via events. A processor transforms these events into their output-format. In case of the json output format, events are almost 1-on-1 serialized to json (there are a few exceptions), and then printed to stderr. Each json serialized event ends with a newline. Each line thus represents a single serialized event.

To use the json output format, run cargo-msrv with the --output-format json option. For example, if you want to find the MSRV, you could run cargo msrv find --output-format json.

In the next section, you can find a description of the common fields of events. The section thereafter gives an overview of each of the supported events, with for each event its event specific fields.

Events and scope

Cargo MSRV currently reports two types of events: unscoped and scoped events. Unscoped events report about an action on a certain point in time, while scoped events report about an action which took place over a period of time.

In the context of the json output format, an unscoped event will print a single json-line to the stderr, while a scoped event will print two json-lines to the stderr (one prior to starting the action, and one after the action has been completed).

Common fields on events

name	optional	values	description
type	no		Identifies a specific event.
scope	yes		A pair of events which mark the start and end of an action. Together these two individual events are called a scoped event.
scope.id	no		A unique id to match up the two events marking the begin and end of an action. The current incremental nature is an implementation detail and not guaranteed.
scope.marker	no	"start" or "end"	Whether the event marks the beginning or the end of the action

The type field can be used to identify a specific event.

The scope field is only present for scoped events. The start value (on the marker subfield) marks the start of a scoped event, while end marks the end of a scoped event.

List of events

Event: `Meta`

type: meta

description: Reports metadata about the currently running cargo-msrv program instance.

fields:

name	description
instance	Name of the running `cargo-msrv` program as defined on compile time. This will usually be `cargo-msrv`.
version	Version of the running `cargo-msrv` program as defined on compile time.
sha_short	Short SHA hash of the git commit used to compile and build `cargo-msrv`.
target_triple	Target triple of toolchain used to compile and build `cargo-msrv`.
cargo_features	Features which were enabled during the compilation of `cargo-msrv`.
rustc	Version of `rustc` used to compile `cargo-msrv`.

example:

{
  "type": "meta",
  "instance": "cargo-msrv",
  "version": "0.15.1",
  "sha_short": "79582b6",
  "target_triple": "x86_64-pc-windows-msvc",
  "cargo_features": "default,rust_releases_dist_source",
  "rustc": "1.62.0"
}

Event: `FetchIndex`

type: fetch_index

description: Prior to determining the MSRV of a crate, we have to figure out which Rust versions are available. We obtain those using the rust-releases library. The FetchIndex event reports that the index is being fetched, and details which source is used.

fields:

name	description
source	Place from where the available Rust releases are obtained

example:

{
  "type": "fetch_index",
  "source": "rust_changelog",
  "scope": "start"
}
{
  "type": "fetch_index",
  "source": "rust_changelog",
  "scope": "end"
}

Event: `CheckToolchain`

type: check_toolchain

description: The primary way for cargo-msrv to determine whether a given Rust toolchain is compatible with your crate, is by installing a toolchain and using it to check a crate for compatibility with this toolchain. The CheckToolchain event is wrapped around this process and notifies you about the start and end of this process. This event is called as a scoped event, and within it's scope, you'll find the following events: setup_toolchain, check_method and check_result, which are described in more detail below.

fields:

name	description
toolchain	The toolchain to be located or installed
toolchain.version	The Rust version of the toolchain
toolchain.target	The target-triple of the toolchain

example:

{
  "type": "check_toolchain",
  "toolchain": {
    "version": "1.35.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "scope": "start"
}
{
  "type": "check_toolchain",
  "toolchain": {
    "version": "1.35.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "scope": "end"
}

Event: `SetupToolchain`

type: setup_toolchain

fields:

name	description
toolchain	The toolchain to be located or installed
toolchain.version	The Rust version of the toolchain
toolchain.target	The target-triple of the toolchain

example:

{
  "type": "setup_toolchain",
  "toolchain": {
    "version": "1.47.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "scope": "start"
}
{
  "type": "setup_toolchain",
  "toolchain": {
    "version": "1.47.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "scope": "end"
}

Event: `CheckMethod`

type: check_method

description: Reports which method has been used to check whether a toolchain is compatible with a crate.

fields:

name	optional	condition	description
toolchain	no		The toolchain to be located or installed
toolchain.version	no		The Rust version of the toolchain
toolchain.target	no		The target-triple of the toolchain
method	no		The method used to check for compatibility
method.type	no		The type of method
method.args	no	method.type = `rustup_run`	The arguments provided to rustup
method.path	yes	method.type = `rustup_run`	The path provided to rustup, if any

example:

{
  "type": "check_method",
  "toolchain": {
    "version": "1.37.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "method": {
    "rustup_run": {
      "args": [
        "1.37.0-x86_64-pc-windows-msvc",
        "cargo",
        "check"
      ],
      "path": "..\\air3\\"
    }
  }
}

Event: `CheckResult`

type: check_result

description: Reports the result of a cargo-msrv compatibility check.

fields:

name	optional	condition	description
toolchain	no		The toolchain to be located or installed
toolchain.version	no		The Rust version of the toolchain
toolchain.target	no		The target-triple of the toolchain
is_compatible	no		Boolean value stating compatibility
error	yes	is_compatible = `false`	Error message of a failed compatibility check, if any

example:

{
  "type": "check_result",
  "toolchain": {
    "version": "1.38.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "is_compatible": true
}

{
  "type": "check_result",
  "toolchain": {
    "version": "1.37.0",
    "target": "x86_64-pc-windows-msvc"
  },
  "is_compatible": false,
  "error": "error: failed to parse lock file at: .\\air3\\Cargo.lock\n\nCaused by:\ninvalid serialized PackageId for key `package.dependencies`\n"
}

Event: `AuxiliaryOutput`

type: auxiliary_output

description: Reports about additional output written by cargo-msrv when applicable. For example, if the --write-msrv or --write-toolchain-file flag is provided, the MSRV will be written to the Cargo manifest or the Rust toolchain file respectively. The act of writing this (additional) output is reported by this event.

fields:

name	optional	condition	description
destination	no		The destination of the auxiliary output
destination.type	no		Type of destination, currently only "file"
destination.path	no	if destination.type = `file`	Path of the written or amended file
item	no		What kind of output is written
item.type	no		Type of output item
item.kind	no	if item.type = `msrv`	To which field the MSRV was written in the Cargo manifest, "rust-version" or "metadata_fallback"
item.kind	no	if item.type = `toolchain_file`	Which toolchain file kind was written, "legacy" or "toml"

example:

{
  "type": "auxiliary_output",
  "destination": {
    "type": "file",
    "path": "..\\air3\\Cargo.toml"
  },
  "item": {
    "type": "msrv",
    "kind": "rust_version"
  }
}

Event: `Progress`

type: progress

description: Reports on the progress of an ongoing MSRV search.

fields:

name	optional	description
current	no	Index of the currently running check into the sorted search space. Starts at `0`.
search_space_size	no	The size of the search space.
iteration	no	How many iterations have been completed, plus one for the currently running iteration. Starts at `1`.

Event: `SubcommandInit`

type: subcommand_init

description: Reports the start of a subcommand flow.

fields:

name	optional	condition	description
subcommand_id	no		A name identifying the subcommand

Event: `SubcommandResult`

type: subcommand_result

description: Reports the outcome of a subcommand flow.

fields:

name	optional	condition	description
subcommand_id	no		A name identifying the subcommand

result	no	subcommand_id = `find`	Result of find command
result.success	no	subcommand_id = `find`	Whether the MSRV was found or not
result.version	no	subcommand_id = `find` and result.success = `true`	The Minimum Supported Rust Version (MSRV)

result	no	subcommand_id = `list`	Result of list command
result.variant	no	subcommand_id = `list`	Type of list output. Either `direct-deps` or `ordered-by-msrv`.
result.list	no	subcommand_id = `list` and result.variant = `direct-deps`	List of direct dependencies of the selected crate
result.list.name	no	subcommand_id = `list` and result.variant = `direct-deps`	Name of the crate
result.list.version	no	subcommand_id = `list` and result.variant = `direct-deps`	Version of the crate
result.list.msrv	no	subcommand_id = `list` and result.variant = `direct-deps`	MSRV of the crate if any, `null` if the MSRV is not set
result.list.dependencies	no	subcommand_id = `list` and result.variant = `direct-deps`	Dependencies of the given crate, relevant for the MSRV
result.list	no	subcommand_id = `list` and result.variant = `ordered-by-msrv`	List of all dependencies relevant for the MSRV, categorised by their MSRV
result.list.msrv	no	subcommand_id = `list` and result.variant = `ordered-by-msrv`	A value for the MSRV specified by at least one crate
result.list.dependencies	no	subcommand_id = `list` and result.variant = `ordered-by-msrv`	List of dependencies which specified the same value for the MSRV

result	no	subcommand_id = `set`	Result of set command
result.version	no	subcommand_id = `set`	Which version was set as MSRV
result.manifest_path	no	subcommand_id = `set`	Relative path of file where the MSRV was written to

result	no	subcommand_id = `show`	Result of show command
result.version	no	subcommand_id = `show`	MSRV as set for the given crate
result.manifest_path	no	subcommand_id = `show`	Relative path of file where the MSRV was read from

result	no	subcommand_id = `verify`	Result of verify command
result.toolchain	no	subcommand_id = `verify`	The toolchain to be located or installed
result.toolchain.version	no	subcommand_id = `verify`	The Rust version of the verified toolchain
result.toolchain.target	no	subcommand_id = `verify`	The target-triple of the verified toolchain
result.is_compatible	no	subcommand_id = `verify`	Boolean value stating compatibility
result.error	yes	subcommand_id = `verify` and result.is_compatible = `false`	Error message of a failed verify check, if any

example 1: find

{
  "type": "subcommand_result",
  "subcommand_id": "find",
  "result": {
    "version": "1.38.0",
    "success": true
  }
}

example 2: list with direct-deps

{
  "type": "subcommand_result",
  "subcommand_id": "list",
  "result": {
    "variant": "direct-deps",
    "list": [
      {
        "name": "crossbeam-channel",
        "version": "0.5.4",
        "msrv": "1.36.0",
        "dependencies": [
          "cfg-if",
          "crossbeam-utils",
          "num_cpus",
          "rand",
          "signal-hook"
        ]
      }
    ]
  }
}

Formatted:

{
  "type": "subcommand_result",
  "subcommand_id": "list",
  "result": {
    "variant": "direct-deps",
    "list": [
      {
        "name": "crossbeam-channel",
        "version": "0.5.4",
        "msrv": "1.36.0",
        "dependencies": [
          "cfg-if",
          "crossbeam-utils",
          "num_cpus",
          "rand",
          "signal-hook"
        ]
      }
    ]
  }
}

example 3: list with ordered-by-msrv

{
  "type": "subcommand_result",
  "subcommand_id": "list",
  "result": {
    "variant": "ordered-by-msrv",
    "list": [
      {
        "msrv": "1.38.0",
        "dependencies": [
          "storyteller"
        ]
      },
      {
        "msrv": "1.36.0",
        "dependencies": [
          "crossbeam-channel",
          "crossbeam-utils"
        ]
      },
      {
        "msrv": null,
        "dependencies": [
          "cfg-if",
          "lazy_static"
        ]
      }
    ]
  }
}

Formatted:

{
  "type": "subcommand_result",
  "subcommand_id": "list",
  "result": {
    "variant": "ordered-by-msrv",
    "list": [
      {
        "msrv": "1.38.0",
        "dependencies": [
          "storyteller"
        ]
      },
      {
        "msrv": "1.36.0",
        "dependencies": [
          "crossbeam-channel",
          "crossbeam-utils"
        ]
      },
      {
        "msrv": null,
        "dependencies": [
          "cfg-if",
          "lazy_static"
        ]
      }
    ]
  }
}

example 5: set:

{
  "type": "subcommand_result",
  "subcommand_id": "set",
  "result": {
    "version": "1.38.0",
    "manifest_path": "..\\air3\\Cargo.toml"
  }
}

example 6: show:

{
  "type": "subcommand_result",
  "subcommand_id": "show",
  "result": {
    "version": "1.38.0",
    "manifest_path": "..\\air3\\Cargo.toml"
  }
}

example 7: verify:

{
  "type": "subcommand_result",
  "subcommand_id": "verify",
  "result": {
    "toolchain": {
      "version": "1.38.0",
      "target": "x86_64-pc-windows-msvc"
    },
    "is_compatible": true
  }
}

Event: `TerminateWithFailure`

type: terminate_with_failure

description: Reports about failure which led to program termination with a non-zero exit code.

fields:

name	optional	description
reason	no	Reason of failure
reason.description	no	Describes why cargo-msrv will terminate with a non-zero exit code

example:

{
  "type": "terminate_with_failure",
  "reason": {
    "description": "MSRV was not specified in Cargo manifest at '..\\air\\Cargo.toml'"
  }
}

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