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

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:

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:

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:

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

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 SetupToolchain event reports about the process of locating or installing a given toolchain.

fields:

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:

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:

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:

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:

Event: SubcommandInit

type: subcommand_init

description: Reports the start of a subcommand flow.

fields:

Event: SubcommandResult

type: subcommand_result

description: Reports the outcome of a subcommand flow.

fields:

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:

example:

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