{ "field_artifacts_list":
  { "doc": ["Query list of artifacts from target_field's targets"]
  , "vars": ["fieldname", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "expression":
    { "type": "foreach"
    , "var": "x"
    , "range": {"type": "FIELD", "name": {"type": "var", "name": "fieldname"}}
    , "body":
      { "type": "DEP_ARTIFACTS"
      , "dep": {"type": "var", "name": "x"}
      , "transition":
        {"type": "var", "name": "transition", "default": {"type": "empty_map"}}
      }
    }
  }
, "field_artifacts":
  { "doc": ["Query and merge artifacts from target_field's targets"]
  , "vars": ["fieldname", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "imports": {"artifacts_list": "field_artifacts_list"}
  , "expression":
    { "type": "disjoint_map_union"
    , "msg":
      ["artifacts", {"type": "var", "name": "fieldname"}, "must not overlap"]
    , "$1": {"type": "CALL_EXPRESSION", "name": "artifacts_list"}
    }
  }
, "field_runfiles_list":
  { "doc": ["Query list of runfiles from target_field's targets"]
  , "vars": ["fieldname", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "expression":
    { "type": "foreach"
    , "var": "x"
    , "range": {"type": "FIELD", "name": {"type": "var", "name": "fieldname"}}
    , "body":
      { "type": "DEP_RUNFILES"
      , "dep": {"type": "var", "name": "x"}
      , "transition":
        {"type": "var", "name": "transition", "default": {"type": "empty_map"}}
      }
    }
  }
, "field_runfiles":
  { "doc": ["Query and merge runfiles from target_field's targets"]
  , "vars": ["fieldname", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "imports": {"runfiles_list": "field_runfiles_list"}
  , "expression":
    { "type": "disjoint_map_union"
    , "msg":
      ["runfiles", {"type": "var", "name": "fieldname"}, "must not overlap"]
    , "$1": {"type": "CALL_EXPRESSION", "name": "runfiles_list"}
    }
  }
, "field_provider_list":
  { "doc": ["Query list of providers from targets' provides map"]
  , "vars": ["fieldname", "provider", "transition", "default"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "provider": ["The name of the map provider in the provides map."]
    , "transition": ["The optional configuration transition for the targets."]
    , "default": ["The default if the provider was not found (default: [])."]
    }
  , "expression":
    { "type": "foreach"
    , "var": "x"
    , "range": {"type": "FIELD", "name": {"type": "var", "name": "fieldname"}}
    , "body":
      { "type": "DEP_PROVIDES"
      , "dep": {"type": "var", "name": "x"}
      , "provider": {"type": "var", "name": "provider"}
      , "transition":
        {"type": "var", "name": "transition", "default": {"type": "empty_map"}}
      , "default": {"type": "var", "name": "default", "default": []}
      }
    }
  }
, "field_map_provider":
  { "doc": ["Query and merge map-providers from targets' provides map"]
  , "vars": ["fieldname", "provider", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "provider": ["The name of the map provider in the provides map."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "imports": {"provider_list": "field_provider_list"}
  , "expression":
    { "type": "disjoint_map_union"
    , "msg":
      ["Overlapping entries in provider", {"type": "var", "name": "provider"}]
    , "$1":
      { "type": "let*"
      , "bindings": [["default", {"type": "empty_map"}]]
      , "body": {"type": "CALL_EXPRESSION", "name": "provider_list"}
      }
    }
  }
, "field_list_provider":
  { "doc": ["Query and merge list-providers from targets' provides map"]
  , "vars": ["fieldname", "provider", "transition"]
  , "vars_doc":
    { "fieldname": ["The name of the target_field to query."]
    , "provider": ["The name of the list provider in the provides map."]
    , "transition": ["The optional configuration transition for the targets."]
    }
  , "imports": {"provider_list": "field_provider_list"}
  , "expression":
    {"type": "++", "$1": {"type": "CALL_EXPRESSION", "name": "provider_list"}}
  }
, "action_env":
  { "vars": ["ENV"]
  , "expression":
    { "type": "map_union"
    , "$1":
      [ {"type": "singleton_map", "key": "PATH", "value": "/bin:/usr/bin"}
      , {"type": "var", "name": "ENV", "default": {"type": "empty_map"}}
      ]
    }
  }
, "stage_singleton_field":
  { "vars": ["fieldname", "transition", "location"]
  , "expression":
    { "type": "assert_non_empty"
    , "msg":
      ["No artifact specified in field", {"type": "var", "name": "fieldname"}]
    , "$1":
      { "type": "disjoint_map_union"
      , "msg":
        [ "Expecting (essentially) a single artifact in field"
        , {"type": "var", "name": "fieldname"}
        ]
      , "$1":
        { "type": "foreach"
        , "var": "src"
        , "range":
          {"type": "FIELD", "name": {"type": "var", "name": "fieldname"}}
        , "body":
          { "type": "disjoint_map_union"
          , "$1":
            { "type": "foreach"
            , "var": "artifact"
            , "range":
              { "type": "values"
              , "$1":
                { "type": "DEP_ARTIFACTS"
                , "dep": {"type": "var", "name": "src"}
                , "transition":
                  { "type": "var"
                  , "name": "transition"
                  , "default": {"type": "empty_map"}
                  }
                }
              }
            , "body":
              { "type": "singleton_map"
              , "key": {"type": "var", "name": "location"}
              , "value": {"type": "var", "name": "artifact"}
              }
            }
          }
        }
      }
    }
  }
, "stage_artifact_to_singleton_field":
  { "vars": ["artifact", "fieldname", "transition"]
  , "expression":
    { "type": "let*"
    , "bindings":
      [ [ "location"
        , { "type": "++"
          , "$1":
            { "type": "foreach"
            , "var": "src"
            , "range":
              {"type": "FIELD", "name": {"type": "var", "name": "fieldname"}}
            , "body":
              { "type": "keys"
              , "$1":
                { "type": "DEP_ARTIFACTS"
                , "dep": {"type": "var", "name": "src"}
                , "transition":
                  { "type": "var"
                  , "name": "transition"
                  , "default": {"type": "empty_map"}
                  }
                }
              }
            }
          }
        ]
      , [ "staged_artifact"
        , { "type": "foreach_map"
          , "range": {"type": "var", "name": "artifact"}
          , "var_val": "val"
          , "body":
            { "type": "foreach"
            , "range": {"type": "var", "name": "location"}
            , "var": "pos"
            , "body":
              { "type": "singleton_map"
              , "key": {"type": "var", "name": "pos"}
              , "value": {"type": "var", "name": "val"}
              }
            }
          }
        ]
      ]
    , "body":
      { "type": "disjoint_map_union"
      , "$1": {"type": "++", "$1": {"type": "var", "name": "staged_artifact"}}
      }
    }
  }
, "nub_left":
  { "doc": ["Removes all but the leftmost duplicate from the list."]
  , "vars": ["list"]
  , "vars_doc": {"list": ["The list to remove duplicates from."]}
  , "expression":
    { "type": "let*"
    , "bindings":
      [ ["list", {"type": "reverse", "$1": {"type": "var", "name": "list"}}]
      , ["list", {"type": "nub_right", "$1": {"type": "var", "name": "list"}}]
      , ["list", {"type": "reverse", "$1": {"type": "var", "name": "list"}}]
      ]
    , "body": {"type": "var", "name": "list"}
    }
  }
}