{ "defaults":
  { "doc":
    [ "A rule to provide defaults for the usage of the shell"
    , ""
    , "All targets using invocations of the shell use the target"
    , "[\"shel\", \"defaults\"] to determine which shell to use and how to"
    , "invoke it. The definition of this default target is probably the only"
    , "meaningful use of this rule."
    ]
  , "target_fields": ["base", "toolchain"]
  , "string_fields": ["sh", "PATH", "bin dirs"]
  , "field_doc":
    { "base": ["Other targets (using the same rule) to inherit values from."]
    , "toolchain":
      [ "Optional toolchain directory. A collection of artifacts that"
      , "form the toolchain, in particular the shell itself, where not taken"
      , "from the ambient host environment."
      , "Values provided from base are extended."
      , "This field is built for the host."
      ]
    , "sh":
      [ "The name of the sh binary; if the the field \"toolchain\" is"
      , "not empty, the value is interpreted as relative to the toolchain"
      , "directory."
      ]
    , "PATH":
      [ "Paths for looking up system tools."
      , "Specifying this field extends values from \"base\"."
      ]
    , "bin dirs":
      [ "Directories of the toolchain that contain additional binaries."
      , "Shell-specific rules will add those into PATH."
      ]
    }
  , "config_vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
  , "imports":
    { "for host": ["transitions", "for host"]
    , "artifacts_list": ["", "field_artifacts_list"]
    , "base-provides-list": ["CC", "defaults-base-provides-list"]
    , "base-provides-++": ["CC", "defaults-base-provides-++"]
    , "base-provides": ["CC", "defaults-base-provides"]
    }
  , "config_transitions":
    {"toolchain": [{"type": "CALL_EXPRESSION", "name": "for host"}]}
  , "expression":
    { "type": "let*"
    , "bindings":
      [ [ "TOOLCHAIN"
        , { "type": "disjoint_map_union"
          , "msg": "toolchain artifacts must not overlap"
          , "$1":
            { "type": "++"
            , "$1":
              [ { "type": "let*"
                , "bindings":
                  [ ["provider", "TOOLCHAIN"]
                  , ["default", {"type": "empty_map"}]
                  ]
                , "body":
                  {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
                }
              , { "type": "let*"
                , "bindings":
                  [ ["fieldname", "toolchain"]
                  , [ "transition"
                    , {"type": "CALL_EXPRESSION", "name": "for host"}
                    ]
                  ]
                , "body": {"type": "CALL_EXPRESSION", "name": "artifacts_list"}
                }
              ]
            }
          }
        ]
      , [ "sh"
        , { "type": "if"
          , "cond": {"type": "FIELD", "name": "sh"}
          , "then": {"type": "FIELD", "name": "sh"}
          , "else":
            { "type": "let*"
            , "bindings": [["provider", "sh"]]
            , "body": {"type": "CALL_EXPRESSION", "name": "base-provides"}
            }
          }
        ]
      , [ "NON_SYSTEM_TOOLS"
        , { "type": "map_union"
          , "$1":
            { "type": "++"
            , "$1":
              [ [ { "type": "let*"
                  , "bindings":
                    [ ["provider", "NON_SYSTEM_TOOLS"]
                    , ["default", {"type": "empty_map"}]
                    ]
                  , "body":
                    {"type": "CALL_EXPRESSION", "name": "base-provides"}
                  }
                ]
              , { "type": "if"
                , "cond": {"type": "FIELD", "name": "sh"}
                , "then":
                  [ { "type": "singleton_map"
                    , "key": "sh"
                    , "value":
                      { "type": "if"
                      , "cond": {"type": "FIELD", "name": "toolchain"}
                      , "then": true
                      , "else": false
                      }
                    }
                  ]
                }
              ]
            }
          }
        ]
      , [ "PATH"
        , { "type": "nub_left"
          , "$1":
            { "type": "++"
            , "$1":
              [ {"type": "FIELD", "name": "PATH"}
              , { "type": "let*"
                , "bindings": [["provider", "PATH"]]
                , "body":
                  {"type": "CALL_EXPRESSION", "name": "base-provides-++"}
                }
              ]
            }
          }
        ]
      , [ "bin dirs"
        , { "type": "nub_left"
          , "$1":
            { "type": "++"
            , "$1":
              [ {"type": "FIELD", "name": "bin dirs"}
              , { "type": "let*"
                , "bindings": [["provider", "bin dirs"]]
                , "body":
                  {"type": "CALL_EXPRESSION", "name": "base-provides-++"}
                }
              ]
            }
          }
        ]
      ]
    , "body":
      { "type": "RESULT"
      , "provides":
        { "type": "env"
        , "vars": ["TOOLCHAIN", "sh", "NON_SYSTEM_TOOLS", "PATH", "bin dirs"]
        }
      }
    }
  }
}