# Module cargo::util::context

source ·
Expand description

Cargo’s config system.

The `GlobalContext` object contains general information about the environment, and provides access to Cargo’s configuration files.

### §Config value API

The primary API for fetching user-defined config values is the `GlobalContext::get` method. It uses `serde` to translate config values to a target type.

There are a variety of helper types for deserializing some common formats:

- `value::Value`: This type provides access to the location where the config value was defined.
- `ConfigRelativePath`: For a path that is relative to where it is defined.
- `PathAndArgs`: Similar to `ConfigRelativePath`, but also supports a list of arguments, useful for programs to execute.
- `StringList`: Get a value that is either a list or a whitespace split string.

### §Map key recommendations

Handling tables that have arbitrary keys can be tricky, particularly if it should support environment variables. In general, if possible, the caller should pass the full key path into the `get()` method so that the config deserializer can properly handle environment variables (which need to be uppercased, and dashes converted to underscores).

A good example is the `[target]` table. The code will request `target.$TRIPLE` and the config system can then appropriately fetch environment variables like `CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER`. Conversely, it is not possible do the same thing for the `cfg()` target tables (because Cargo must fetch all of them), so those do not support environment variables.

Try to avoid keys that are a prefix of another with a dash/underscore. For example `build.target` and `build.target-dir`. This is OK if these are not structs/maps, but if it is a struct or map, then it will not be able to read the environment variable due to ambiguity. (See `ConfigMapAccess` for more details.)

### §Internal API

Internally config values are stored with the `ConfigValue` type after they have been loaded from disk. This is similar to the `toml::Value` type, but includes the definition location. The `get()` method uses serde to translate from `ConfigValue` and environment variables to the caller’s desired type.

## Modules§

- de 🔒
  Support for deserializing configuration via `serde`
- environment 🔒
  Encapsulates snapshotting of environment variables.
- key 🔒
- path 🔒
- target 🔒
- value 🔒
  Deserialization of a `Value<T>` type which tracks where it was deserialized from.

## Macros§

- get_value_typed 🔒

## Structs§

- BuildTargetConfig
  Configuration for `build.target`.
- CargoBuildConfig
- CargoFutureIncompatConfig
- CargoHttpConfig
- CargoNetConfig
- CargoResolverConfig
- CargoSshConfig
- ConfigError
  Internal error for serde errors.
- ConfigKey
  Key for a configuration variable.
- ConfigRelativePath
  Use with the `get` API to fetch a string that will be converted to a `PathBuf`. Relative paths are converted to absolute paths based on the location of the config file.
- CredentialCacheValue
  A previously generated authentication token and the data needed to determine if it can be reused.
- EnvConfigValue
- GlobalContext
  Configuration information for cargo. This is not specific to a build, it is information relating to cargo itself.
- MissingFieldError 🔒
- PathAndArgs
  A config type that is a program to run.
- ProgressConfig
- SslVersionConfigRange
- StringList
  A type to deserialize a list of strings from a toml file.
- TargetCfgConfig
  Config definition of a `[target.'cfg(…)']` table.
- TargetConfig
  Config definition of a `[target]` table or `[host]`.
- TermConfig
- UnmergedStringList
  StringList automatically merges config values with environment values, this instead follows the precedence rules, so that eg. a string list found in the environment will be used instead of one in a config file.
- Value
  A type which can be deserialized as a configuration value which records where it was deserialized from.

## Enums§

- BuildTargetConfigInner 🔒
- CargoFutureIncompatFrequencyConfig
- CargoResolverPrecedence
- ConfigValue
- Definition
  Location where a config value is defined.
- EnvConfigValueInner 🔒
- JobsConfig
  Configuration for `jobs` in `build` section. There are two ways to configure: An integer or a simple string expression.
- ProgressWhen
- SslVersionConfig
  Configuration for `ssl-version` in `http` section There are two ways to configure:
- Tool 🔒
- WhyLoad 🔒
  Indicates why a config value is being loaded.

## Functions§

- disables_multiplexing_for_bad_curl 🔒
  Disable HTTP/2 multiplexing for some broken versions of libcurl.
- homedir
- parse_document 🔒
- progress_or_string 🔒
- save_credentials

## Type Aliases§

- EnvConfig
- OptValue