Merge branch 'rules/oss' into rules/rules-cc-rules

6 files changed, 310 insertions, 120 deletions

diff --git a/CC/EXPRESSIONS b/CC/EXPRESSIONS
index e97ed76..2a5011d 100644
--- a/CC/EXPRESSIONS
+++ b/CC/EXPRESSIONS
@@ -6,9 +6,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "CC"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -21,9 +19,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "CXX"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -36,9 +32,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "AR"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -51,9 +45,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "CFLAGS"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -66,9 +58,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "CXXFLAGS"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -81,9 +71,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "LDFLAGS"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -96,14 +84,25 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "ENV"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       , ["default", {"type": "empty_map"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "map_provider"}
     }
   }
+, "default-PATH":
+  { "vars": ["defaults-transition"]
+  , "imports": {"list_provider": ["./", "..", "field_list_provider"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["fieldname", "defaults"]
+      , ["provider", "PATH"]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
+      ]
+    , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
+    }
+  }
 , "default-TOOLCHAIN":
   { "vars": ["defaults-transition"]
   , "imports": {"map_provider": ["./", "..", "field_map_provider"]}
@@ -112,9 +111,7 @@
     , "bindings":
       [ ["fieldname", "defaults"]
       , ["provider", "TOOLCHAIN"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       , ["default", {"type": "empty_map"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "map_provider"}
@@ -142,29 +139,39 @@
       }
     }
   }
-, "defaults-base-provides":
-  { "doc": ["Query list-provider from 'base' targets (last wins)"]
+, "defaults-base-provides-list":
+  { "doc": ["Query list of providers from 'base' targets"]
   , "vars": ["provider", "default"]
   , "vars_doc":
-    { "provider": ["The name of the list-provider in the provides map."]
+    { "provider": ["The name of the provider in the provides map."]
     , "default": ["The default if provider is missing (default: [])."]
     }
   , "imports": {"provider_list": ["./", "..", "field_provider_list"]}
   , "expression":
     { "type": "let*"
     , "bindings": [["fieldname", "base"]]
+    , "body": {"type": "CALL_EXPRESSION", "name": "provider_list"}
+    }
+  }
+, "defaults-base-provides":
+  { "doc": ["Query provider from 'base' targets (last wins)"]
+  , "vars": ["provider", "default"]
+  , "vars_doc":
+    { "provider": ["The name of the provider in the provides map."]
+    , "default": ["The default if provider is missing (default: [])."]
+    }
+  , "imports": {"base-provides-list": "defaults-base-provides-list"}
+  , "expression":
+    { "type": "foldl"
+    , "var": "next"
+    , "start": {"type": "var", "name": "default", "default": []}
+    , "accum_var": "curr"
+    , "range": {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
     , "body":
-      { "type": "foldl"
-      , "var": "next"
-      , "start": {"type": "var", "name": "default", "default": []}
-      , "accum_var": "curr"
-      , "range": {"type": "CALL_EXPRESSION", "name": "provider_list"}
-      , "body":
-        { "type": "if"
-        , "cond": {"type": "var", "name": "next"}
-        , "then": {"type": "var", "name": "next"}
-        , "else": {"type": "var", "name": "curr"}
-        }
+      { "type": "if"
+      , "cond": {"type": "var", "name": "next"}
+      , "then": {"type": "var", "name": "next"}
+      , "else": {"type": "var", "name": "curr"}
       }
     }
   }
@@ -900,6 +907,7 @@
     , "objects": "objects"
     , "default-AR": "default-AR"
     , "default-ENV": "default-ENV"
+    , "default-PATH": "default-PATH"
     , "default-TOOLCHAIN": "default-TOOLCHAIN"
     , "default-NON_SYSTEM_TOOLS": "default-NON_SYSTEM_TOOLS"
     }
@@ -957,6 +965,36 @@
             ]
           }
         ]
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
+          }
+        ]
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
+                , "$1":
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
+                }
+              }
+            ]
+          }
+        ]
       , ["objects", {"type": "CALL_EXPRESSION", "name": "objects"}]
       , [ "base name"
         , { "type": "if"
@@ -1517,6 +1555,7 @@
     , "flags": "flags"
     , "objects": "objects"
     , "default-ENV": "default-ENV"
+    , "default-PATH": "default-PATH"
     , "default-LDFLAGS": "default-LDFLAGS"
     , "default-TOOLCHAIN": "default-TOOLCHAIN"
     , "default-NON_SYSTEM_TOOLS": "default-NON_SYSTEM_TOOLS"
@@ -1564,6 +1603,36 @@
             ]
           }
         ]
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
+          }
+        ]
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
+                , "$1":
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
+                }
+              }
+            ]
+          }
+        ]
       , ["hdrs", {"type": "empty_map"}]
       , ["objects", {"type": "CALL_EXPRESSION", "name": "objects"}]
       , [ "link-args"
diff --git a/CC/RULES b/CC/RULES
index 96d1db4..fa133e4 100644
--- a/CC/RULES
+++ b/CC/RULES
@@ -26,7 +26,10 @@
       [ "Optional toolchain directory. A collection of artifacts that provide"
       , "the tools CC, CXX, and AR (if needed). Note that only artifacts of"
       , "the specified targets are considered (no runfiles etc.). Specifying"
-      , "this field overlays artifacts from \"base\"."
+      , "this field extends artifacts from \"base\". If the toolchain"
+      , "supports cross-compilation, it should perform a dispatch on the"
+      , "configuration variable \"BUILD_ARCH\" to determine for which"
+      , "architecture to generate code for."
       ]
     , "deps":
       [ "Optional CC libraries any CC library and CC binary implicitly depend"
@@ -66,13 +69,15 @@
       ]
     , "PATH":
       [ "Path for looking up the compilers. Individual paths are joined"
-      , "with \":\"."
+      , "with \":\". Specifying this field extends values from \"base\"."
       ]
     }
-  , "config_vars": ["ARCH", "HOST_ARCH"]
+  , "config_vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
   , "imports":
     { "base-provides": "defaults-base-provides"
-    , "artifacts": ["./", "..", "field_artifacts"]
+    , "base-provides-list": "defaults-base-provides-list"
+    , "artifacts_list": ["./", "..", "field_artifacts_list"]
+    , "nub_left": ["", "nub_left"]
     , "compile-deps": "compile-deps"
     , "compile-args-deps": "compile-args-deps"
     , "link-deps": "link-deps"
@@ -143,23 +148,26 @@
           , "else": {"type": "CALL_EXPRESSION", "name": "base-provides"}
           }
         ]
-      , ["provider", "ENV"]
-      , ["default", {"type": "empty_map"}]
-      , [ "ENV"
-        , { "type": "if"
-          , "cond": {"type": "var", "name": "PATH"}
-          , "then":
-            { "type": "singleton_map"
-            , "key": "PATH"
-            , "value":
-              { "type": "join"
-              , "separator": ":"
-              , "$1": {"type": "var", "name": "PATH"}
+      , ["provider", "PATH"]
+      , [ "PATH"
+        , { "type": "++"
+          , "$1":
+            [ {"type": "var", "name": "PATH"}
+            , { "type": "++"
+              , "$1": {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
               }
-            }
-          , "else": {"type": "CALL_EXPRESSION", "name": "base-provides"}
+            ]
           }
         ]
+      , [ "PATH"
+        , { "type": "let*"
+          , "bindings": [["list", {"type": "var", "name": "PATH"}]]
+          , "body": {"type": "CALL_EXPRESSION", "name": "nub_left"}
+          }
+        ]
+      , ["provider", "ENV"]
+      , ["default", {"type": "empty_map"}]
+      , ["ENV", {"type": "CALL_EXPRESSION", "name": "base-provides"}]
       , ["provider", "NON_SYSTEM_TOOLS"]
       , ["default", {"type": "empty_map"}]
       , [ "NON_SYSTEM_TOOLS"
@@ -226,24 +234,28 @@
       , ["provider", "TOOLCHAIN"]
       , ["default", {"type": "empty_map"}]
       , [ "TOOLCHAIN"
-        , { "type": "map_union"
+        , { "type": "disjoint_map_union"
+          , "msg": "toolchain artifacts may not overlap"
           , "$1":
-            [ {"type": "CALL_EXPRESSION", "name": "base-provides"}
-            , { "type": "if"
-              , "cond": {"type": "FIELD", "name": "toolchain"}
-              , "then":
-                { "type": "let*"
-                , "bindings":
-                  [ ["fieldname", "toolchain"]
-                  , [ "transition"
-                    , {"type": "CALL_EXPRESSION", "name": "for host"}
+            { "type": "++"
+            , "$1":
+              [ {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
+              , { "type": "if"
+                , "cond": {"type": "FIELD", "name": "toolchain"}
+                , "then":
+                  { "type": "let*"
+                  , "bindings":
+                    [ ["fieldname", "toolchain"]
+                    , [ "transition"
+                      , {"type": "CALL_EXPRESSION", "name": "for host"}
+                      ]
                     ]
-                  ]
-                , "body": {"type": "CALL_EXPRESSION", "name": "artifacts"}
+                  , "body":
+                    {"type": "CALL_EXPRESSION", "name": "artifacts_list"}
+                  }
                 }
-              , "else": {"type": "empty_map"}
-              }
-            ]
+              ]
+            }
           }
         ]
       , [ "CFLAGS"
@@ -300,6 +312,7 @@
           , "CXXFLAGS"
           , "LDFLAGS"
           , "AR"
+          , "PATH"
           , "ENV"
           , "TOOLCHAIN"
           , "NON_SYSTEM_TOOLS"
diff --git a/CC/auto/RULES b/CC/auto/RULES
index 247ee01..0e156c9 100644
--- a/CC/auto/RULES
+++ b/CC/auto/RULES
@@ -156,6 +156,7 @@
     , "flags-cc": ["./", "..", "flags-cc"]
     , "flags-cxx": ["./", "..", "flags-cxx"]
     , "default-ENV": ["./", "..", "default-ENV"]
+    , "default-PATH": ["./", "..", "default-PATH"]
     , "default-TOOLCHAIN": ["./", "..", "default-TOOLCHAIN"]
     , "default-NON_SYSTEM_TOOLS": ["./", "..", "default-NON_SYSTEM_TOOLS"]
     }
@@ -222,6 +223,36 @@
             ]
           }
         ]
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
+          }
+        ]
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
+                , "$1":
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
+                }
+              }
+            ]
+          }
+        ]
       , [ "c.flags"
         , { "type": "BLOB"
           , "data":
diff --git a/CC/pkgconfig/EXPRESSIONS b/CC/pkgconfig/EXPRESSIONS
index 4c174c4..535faf6 100644
--- a/CC/pkgconfig/EXPRESSIONS
+++ b/CC/pkgconfig/EXPRESSIONS
@@ -1,6 +1,9 @@
 { "pkgconfig result":
   { "vars": ["ENV", "name", "args", "stage"]
-  , "imports": {"default-ENV": ["./", "..", "default-ENV"]}
+  , "imports":
+    { "default-ENV": ["./", "..", "default-ENV"]
+    , "default-PATH": ["./", "..", "default-PATH"]
+    }
   , "expression":
     { "type": "let*"
     , "bindings":
@@ -12,6 +15,36 @@
             ]
           }
         ]
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
+          }
+        ]
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
+                , "$1":
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
+                }
+              }
+            ]
+          }
+        ]
       , [ "cflags-filename"
         , {"type": "join", "$1": [{"type": "var", "name": "name"}, ".cflags"]}
         ]
diff --git a/CC/proto/EXPRESSIONS b/CC/proto/EXPRESSIONS
index 6be74df..29c205c 100644
--- a/CC/proto/EXPRESSIONS
+++ b/CC/proto/EXPRESSIONS
@@ -6,9 +6,7 @@
     , "bindings":
       [ ["fieldname", "proto-defaults"]
       , ["provider", "PROTOC"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -21,9 +19,7 @@
     , "bindings":
       [ ["fieldname", "proto-defaults"]
       , ["provider", "LDFLAGS"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -36,9 +32,7 @@
     , "bindings":
       [ ["fieldname", "proto-defaults"]
       , ["provider", "GRPC_PLUGIN"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
     }
@@ -51,14 +45,25 @@
     , "bindings":
       [ ["fieldname", "proto-defaults"]
       , ["provider", "ENV"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       , ["default", {"type": "empty_map"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "map_provider"}
     }
   }
+, "default-PATH":
+  { "vars": ["defaults-transition"]
+  , "imports": {"list_provider": ["./", "../..", "field_list_provider"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["fieldname", "proto-defaults"]
+      , ["provider", "PATH"]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
+      ]
+    , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
+    }
+  }
 , "default-TOOLCHAIN":
   { "vars": ["defaults-transition"]
   , "imports": {"map_provider": ["./", "../..", "field_map_provider"]}
@@ -67,9 +72,7 @@
     , "bindings":
       [ ["fieldname", "proto-defaults"]
       , ["provider", "TOOLCHAIN"]
-      , [ "transition"
-        , {"type": "var", "name": "defaults-transition", "default": null}
-        ]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
       , ["default", {"type": "empty_map"}]
       ]
     , "body": {"type": "CALL_EXPRESSION", "name": "map_provider"}
@@ -128,6 +131,7 @@
     , "default-LDFLAGS": "default-LDFLAGS"
     , "default-GRPC_PLUGIN": "default-GRPC_PLUGIN"
     , "default-ENV": "default-ENV"
+    , "default-PATH": "default-PATH"
     , "default-TOOLCHAIN": "default-TOOLCHAIN"
     , "default-NON_SYSTEM_TOOLS": "default-NON_SYSTEM_TOOLS"
     }
@@ -182,7 +186,7 @@
             }
           }
         ]
-      , [ "protoc-ENV"
+      , [ "ENV"
         , { "type": "map_union"
           , "$1":
             [ {"type": "CALL_EXPRESSION", "name": "default-ENV"}
@@ -190,6 +194,36 @@
             ]
           }
         ]
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
+          }
+        ]
+      , [ "protoc-ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
+                , "$1":
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
+                }
+              }
+            ]
+          }
+        ]
       , ["protoc-deps", {"type": "CALL_EXPRESSION", "name": "protoc-deps"}]
       , [ "proto srcs"
         , { "type": "disjoint_map_union"
diff --git a/CC/proto/RULES b/CC/proto/RULES
index ac7a371..8108161 100644
--- a/CC/proto/RULES
+++ b/CC/proto/RULES
@@ -19,7 +19,7 @@
       [ "Optional toolchain directory. A collection of artifacts that provide"
       , "the protobuf compiler and the GRPC plugin (if needed). Note that only"
       , "artifacts of the specified targets are considered (no runfiles etc.)."
-      , "Specifying this field overlays artifacts from \"base\"."
+      , "Specifying this field extends artifacts from \"base\"."
       ]
     , "deps":
       [ "Optional CC libraries the resulting CC proto libraries implicitly"
@@ -51,12 +51,14 @@
       ]
     , "PATH":
       [ "Path for looking up the proto compiler. Individual paths are joined"
-      , "with \":\"."
+      , "with \":\". Specifying this field extends values from \"base\"."
       ]
     }
   , "imports":
     { "base-provides": ["./", "..", "defaults-base-provides"]
-    , "artifacts": ["", "field_artifacts"]
+    , "base-provides-list": ["./", "..", "defaults-base-provides-list"]
+    , "artifacts_list": ["", "field_artifacts_list"]
+    , "nub_left": ["", "nub_left"]
     , "compile-deps": ["CC", "compile-deps"]
     , "compile-args-deps": ["CC", "compile-args-deps"]
     , "link-deps": ["CC", "link-deps"]
@@ -100,23 +102,26 @@
           , "else": {"type": "CALL_EXPRESSION", "name": "base-provides"}
           }
         ]
-      , ["provider", "ENV"]
-      , ["default", {"type": "empty_map"}]
-      , [ "ENV"
-        , { "type": "if"
-          , "cond": {"type": "var", "name": "PATH"}
-          , "then":
-            { "type": "singleton_map"
-            , "key": "PATH"
-            , "value":
-              { "type": "join"
-              , "separator": ":"
-              , "$1": {"type": "var", "name": "PATH"}
+      , ["provider", "PATH"]
+      , [ "PATH"
+        , { "type": "++"
+          , "$1":
+            [ {"type": "var", "name": "PATH"}
+            , { "type": "++"
+              , "$1": {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
               }
-            }
-          , "else": {"type": "CALL_EXPRESSION", "name": "base-provides"}
+            ]
           }
         ]
+      , [ "PATH"
+        , { "type": "let*"
+          , "bindings": [["list", {"type": "var", "name": "PATH"}]]
+          , "body": {"type": "CALL_EXPRESSION", "name": "nub_left"}
+          }
+        ]
+      , ["provider", "ENV"]
+      , ["default", {"type": "empty_map"}]
+      , ["ENV", {"type": "CALL_EXPRESSION", "name": "base-provides"}]
       , ["provider", "NON_SYSTEM_TOOLS"]
       , ["default", {"type": "empty_map"}]
       , [ "NON_SYSTEM_TOOLS"
@@ -160,24 +165,28 @@
       , ["provider", "TOOLCHAIN"]
       , ["default", {"type": "empty_map"}]
       , [ "TOOLCHAIN"
-        , { "type": "map_union"
+        , { "type": "disjoint_map_union"
+          , "msg": "toolchain artifacts may not overlap"
           , "$1":
-            [ {"type": "CALL_EXPRESSION", "name": "base-provides"}
-            , { "type": "if"
-              , "cond": {"type": "FIELD", "name": "toolchain"}
-              , "then":
-                { "type": "let*"
-                , "bindings":
-                  [ ["fieldname", "toolchain"]
-                  , [ "transition"
-                    , {"type": "CALL_EXPRESSION", "name": "for host"}
+            { "type": "++"
+            , "$1":
+              [ {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
+              , { "type": "if"
+                , "cond": {"type": "FIELD", "name": "toolchain"}
+                , "then":
+                  { "type": "let*"
+                  , "bindings":
+                    [ ["fieldname", "toolchain"]
+                    , [ "transition"
+                      , {"type": "CALL_EXPRESSION", "name": "for host"}
+                      ]
                     ]
-                  ]
-                , "body": {"type": "CALL_EXPRESSION", "name": "artifacts"}
+                  , "body":
+                    {"type": "CALL_EXPRESSION", "name": "artifacts_list"}
+                  }
                 }
-              , "else": {"type": "empty_map"}
-              }
-            ]
+              ]
+            }
           }
         ]
       , [ "LDFLAGS"
@@ -215,6 +224,7 @@
           [ "PROTOC"
           , "LDFLAGS"
           , "GRPC_PLUGIN"
+          , "PATH"
           , "ENV"
           , "TOOLCHAIN"
           , "NON_SYSTEM_TOOLS"