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

11 files changed, 693 insertions, 202 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"
diff --git a/EXPRESSIONS b/EXPRESSIONS
index c84ebf4..59efead 100644
--- a/EXPRESSIONS
+++ b/EXPRESSIONS
@@ -273,4 +273,35 @@
       }
     }
   }
+, "reverse_list":
+  { "doc": ["Returns the list in reverse order."]
+  , "vars": ["list"]
+  , "vars_doc": {"list": ["The list to reverse."]}
+  , "expression":
+    { "type": "foldl"
+    , "var": "item"
+    , "start": []
+    , "accum_var": "out"
+    , "range": {"type": "var", "name": "list"}
+    , "body":
+      { "type": "++"
+      , "$1":
+        [[{"type": "var", "name": "item"}], {"type": "var", "name": "out"}]
+      }
+    }
+  }
+, "nub_left":
+  { "doc": ["Removes all but the leftmost duplicate from the list."]
+  , "vars": ["list"]
+  , "vars_doc": {"list": ["The list to remove duplicates from."]}
+  , "imports": {"reverse": "reverse_list"}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["list", {"type": "CALL_EXPRESSION", "name": "reverse"}]
+      , ["list", {"type": "nub_right", "$1": {"type": "var", "name": "list"}}]
+      ]
+    , "body": {"type": "CALL_EXPRESSION", "name": "reverse"}
+    }
+  }
 }
diff --git a/patch/EXPRESSIONS b/patch/EXPRESSIONS
new file mode 100644
index 0000000..7f8ce19
--- /dev/null
+++ b/patch/EXPRESSIONS
@@ -0,0 +1,77 @@
+{ "default-PATCH":
+  { "vars": ["defaults-transition"]
+  , "imports": {"list_provider": ["./", "..", "field_list_provider"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["fieldname", "patch-defaults"]
+      , ["provider", "PATCH"]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
+      ]
+    , "body": {"type": "CALL_EXPRESSION", "name": "list_provider"}
+    }
+  }
+, "default-ENV":
+  { "vars": ["defaults-transition"]
+  , "imports": {"map_provider": ["./", "..", "field_map_provider"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["fieldname", "patch-defaults"]
+      , ["provider", "ENV"]
+      , ["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", "patch-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"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["fieldname", "patch-defaults"]
+      , ["provider", "TOOLCHAIN"]
+      , ["transition", {"type": "var", "name": "defaults-transition"}]
+      , ["default", {"type": "empty_map"}]
+      ]
+    , "body": {"type": "CALL_EXPRESSION", "name": "map_provider"}
+    }
+  }
+, "default-NON_SYSTEM_TOOLS":
+  { "vars": ["defaults-transition"]
+  , "expression":
+    { "type": "map_union"
+    , "$1":
+      { "type": "foreach"
+      , "var": "x"
+      , "range": {"type": "FIELD", "name": "patch-defaults"}
+      , "body":
+        { "type": "DEP_PROVIDES"
+        , "dep": {"type": "var", "name": "x"}
+        , "provider": "NON_SYSTEM_TOOLS"
+        , "transition":
+          { "type": "var"
+          , "name": "defaults-transition"
+          , "default": {"type": "empty_map"}
+          }
+        , "default": {"type": "empty_map"}
+        }
+      }
+    }
+  }
+}
diff --git a/patch/RULES b/patch/RULES
index b1ba95e..712a487 100644
--- a/patch/RULES
+++ b/patch/RULES
@@ -1,18 +1,156 @@
-{ "file":
+{ "defaults":
+  { "doc":
+    [ "A rule to provide defaults."
+    , "All targets take their defaults for PATCH from the target"
+    , "[\"\", \"defaults\"]. This is probably the only sensible"
+    , "use of this rule. As targets form a different root, the defaults"
+    , "can be provided without changing this directory."
+    ]
+  , "target_fields": ["base", "toolchain"]
+  , "string_fields": ["PATCH", "PATH", "SYSTEM_TOOLS"]
+  , "field_doc":
+    { "base": ["Other targets (using the same rule) to inherit values from."]
+    , "toolchain":
+      [ "Optional toolchain directory. A collection of artifacts that provide"
+      , "the tool PATCH. Note that only artifacts of"
+      , "the specified targets are considered (no runfiles etc.). Specifying"
+      , "this field extends artifacts from \"base\"."
+      ]
+    , "PATCH": ["The patch binary to use"]
+    , "SYSTEM_TOOLS":
+      [ "List of tools (\"PATCH\") that should be taken from"
+      , "the system instead of from \"toolchain\" (if specified)."
+      ]
+    , "PATH":
+      [ "Path for looking up the compilers. Individual paths are joined"
+      , "with \":\". Specifying this field extends values from \"base\"."
+      ]
+    }
+  , "config_vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
+  , "imports":
+    { "base-provides": ["CC", "defaults-base-provides"]
+    , "base-provides-list": ["CC", "defaults-base-provides-list"]
+    , "artifacts_list": ["", "field_artifacts_list"]
+    , "nub_left": ["", "nub_left"]
+    , "for host": ["transitions", "for host"]
+    }
+  , "config_transitions":
+    {"toolchain": [{"type": "CALL_EXPRESSION", "name": "for host"}]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ ["PATCH", {"type": "FIELD", "name": "PATCH"}]
+      , ["PATH", {"type": "FIELD", "name": "PATH"}]
+      , ["provider", "PATCH"]
+      , [ "PATCH"
+        , { "type": "if"
+          , "cond": {"type": "var", "name": "PATCH"}
+          , "then": {"type": "var", "name": "PATCH"}
+          , "else": {"type": "CALL_EXPRESSION", "name": "base-provides"}
+          }
+        ]
+      , ["provider", "PATH"]
+      , [ "PATH"
+        , { "type": "++"
+          , "$1":
+            [ {"type": "var", "name": "PATH"}
+            , { "type": "++"
+              , "$1": {"type": "CALL_EXPRESSION", "name": "base-provides-list"}
+              }
+            ]
+          }
+        ]
+      , [ "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"
+        , { "type": "map_union"
+          , "$1":
+            { "type": "++"
+            , "$1":
+              [ [{"type": "CALL_EXPRESSION", "name": "base-provides"}]
+              , { "type": "if"
+                , "cond": {"type": "FIELD", "name": "PATCH"}
+                , "then":
+                  [ { "type": "singleton_map"
+                    , "key": "PATCH"
+                    , "value":
+                      { "type": "if"
+                      , "cond": {"type": "FIELD", "name": "toolchain"}
+                      , "then": true
+                      , "else": false
+                      }
+                    }
+                  ]
+                }
+              , { "type": "foreach"
+                , "range": {"type": "FIELD", "name": "SYSTEM_TOOLS"}
+                , "var": "tool"
+                , "body":
+                  { "type": "singleton_map"
+                  , "key": {"type": "var", "name": "tool"}
+                  , "value": false
+                  }
+                }
+              ]
+            }
+          }
+        ]
+      , ["provider", "TOOLCHAIN"]
+      , ["default", {"type": "empty_map"}]
+      , [ "TOOLCHAIN"
+        , { "type": "disjoint_map_union"
+          , "msg": "toolchain artifacts may not overlap"
+          , "$1":
+            { "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_list"}
+                  }
+                }
+              ]
+            }
+          }
+        ]
+      ]
+    , "body":
+      { "type": "RESULT"
+      , "provides":
+        { "type": "env"
+        , "vars": ["PATCH", "PATH", "ENV", "TOOLCHAIN", "NON_SYSTEM_TOOLS"]
+        }
+      }
+    }
+  }
+, "file":
   { "doc": ["Replace a file, logically in place, by a patched version"]
   , "target_fields": ["src", "patch"]
-  , "string_fields": ["patch-part"]
   , "config_vars": ["PATCH", "ENV"]
+  , "implicit": {"patch-defaults": ["defaults"]}
   , "field_doc":
     { "src":
       [ "The single source file to patch, typically an explicit file reference."
       ]
     , "patch": ["The patch to apply."]
-    , "patch-part":
-      [ "If the patch contains hunks for multiple files, only apply hunks for"
-      , "the specified file path. Individual directory components are joined"
-      , "with \"/\". Note that the patch must be provided in unified format."
-      ]
     }
   , "artifacts_doc":
     ["The patched file, staged to the position the of the original file"]
@@ -20,104 +158,144 @@
   , "imports":
     { "stage_field": ["./", "..", "stage_singleton_field"]
     , "stage_artifact": ["./", "..", "stage_artifact_to_singleton_field"]
+    , "default-PATCH": "default-PATCH"
+    , "default-TOOLCHAIN": "default-TOOLCHAIN"
+    , "default-ENV": "default-ENV"
+    , "default-PATH": "default-PATH"
+    , "default-NON_SYSTEM_TOOLS": "default-NON_SYSTEM_TOOLS"
     }
   , "expression":
     { "type": "let*"
     , "bindings":
-      [ [ "orig"
-        , { "type": "let*"
-          , "bindings": [["fieldname", "src"], ["location", "orig"]]
-          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
+      [ ["TOOLCHAIN_DIR", "toolchain"]
+      , ["TOOLCHAIN", {"type": "CALL_EXPRESSION", "name": "default-TOOLCHAIN"}]
+      , [ "TOOLCHAIN"
+        , { "type": "to_subdir"
+          , "subdir": {"type": "var", "name": "TOOLCHAIN_DIR"}
+          , "$1": {"type": "var", "name": "TOOLCHAIN"}
           }
         ]
-      , [ "patch"
-        , { "type": "let*"
-          , "bindings": [["fieldname", "patch"], ["location", "patch"]]
-          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
+      , [ "NON_SYSTEM_TOOLS"
+        , {"type": "CALL_EXPRESSION", "name": "default-NON_SYSTEM_TOOLS"}
+        ]
+      , [ "PATCH"
+        , { "type": "var"
+          , "name": "PATCH"
+          , "default":
+            { "type": "join"
+            , "$1":
+              { "type": "++"
+              , "$1":
+                [ { "type": "if"
+                  , "cond":
+                    { "type": "lookup"
+                    , "key": "PATCH"
+                    , "map": {"type": "var", "name": "NON_SYSTEM_TOOLS"}
+                    }
+                  , "then":
+                    ["./", {"type": "var", "name": "TOOLCHAIN_DIR"}, "/"]
+                  }
+                , {"type": "CALL_EXPRESSION", "name": "default-PATCH"}
+                ]
+              }
+            }
+          }
+        ]
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "CALL_EXPRESSION", "name": "default-ENV"}
+            , {"type": "var", "name": "ENV", "default": {"type": "empty_map"}}
+            ]
           }
         ]
-      , [ "patch-part"
-        , { "type": "join"
-          , "separator": "\\/"
-          , "$1": {"type": "FIELD", "name": "patch-part"}
+      , [ "ENV_PATH"
+        , { "type": "lookup"
+          , "map": {"type": "var", "name": "ENV"}
+          , "key": "PATH"
           }
         ]
-      , [ "splitpatch"
-        , { "type": "BLOB"
-          , "data":
-            { "type": "join"
-            , "separator": "\n"
-            , "$1":
-              [ "set -e"
-              , { "type": "join"
+      , [ "ENV"
+        , { "type": "map_union"
+          , "$1":
+            [ {"type": "var", "name": "ENV"}
+            , { "type": "singleton_map"
+              , "key": "PATH"
+              , "value":
+                { "type": "join"
+                , "separator": ":"
                 , "$1":
-                  [ { "type": "join_cmd"
-                    , "$1":
-                      [ "sed"
-                      , "-n"
-                      , { "type": "join"
-                        , "$1":
-                          [ "/^--- "
-                          , {"type": "var", "name": "patch-part"}
-                          , "/,"
-                          , "/^[^-+@\\ ]\\|^---\\ /p"
-                          ]
-                        }
-                      ]
-                    }
-                  , " $1 | sed '$d' > patch"
-                  ]
+                  { "type": "++"
+                  , "$1":
+                    [ {"type": "CALL_EXPRESSION", "name": "default-PATH"}
+                    , { "type": "if"
+                      , "cond": {"type": "var", "name": "ENV_PATH"}
+                      , "then": [{"type": "var", "name": "ENV_PATH"}]
+                      }
+                    ]
+                  }
                 }
-              ]
-            }
+              }
+            ]
+          }
+        ]
+      , [ "orig"
+        , { "type": "let*"
+          , "bindings": [["fieldname", "src"], ["location", "orig"]]
+          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
           }
         ]
       , [ "patch"
-        , { "type": "if"
-          , "cond": {"type": "var", "name": "patch-part"}
-          , "then":
-            { "type": "ACTION"
-            , "inputs":
-              { "type": "map_union"
+        , { "type": "let*"
+          , "bindings": [["fieldname", "patch"], ["location", "patch"]]
+          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
+          }
+        ]
+      , [ "script"
+        , { "type": "singleton_map"
+          , "key": "run_patch.sh"
+          , "value":
+            { "type": "BLOB"
+            , "data":
+              { "type": "join"
+              , "separator": "\n"
               , "$1":
-                [ { "type": "to_subdir"
-                  , "subdir": "in"
-                  , "$1": {"type": "var", "name": "patch"}
-                  }
-                , { "type": "singleton_map"
-                  , "key": "splitpatch"
-                  , "value": {"type": "var", "name": "splitpatch"}
+                [ "set -e"
+                , "cp orig patched"
+                , "chmod +w patched"
+                , { "type": "join"
+                  , "$1":
+                    [ { "type": "join_cmd"
+                      , "$1":
+                        [ {"type": "var", "name": "PATCH", "default": "patch"}
+                        , "patched"
+                        , "patch"
+                        ]
+                      }
+                    , " >log || (cat log && exit 1)"
+                    ]
                   }
                 ]
               }
-            , "outs": ["patch"]
-            , "cmd": ["sh", "./splitpatch", "in/patch"]
-            , "env":
-              {"type": "var", "name": "ENV", "default": {"type": "empty_map"}}
             }
-          , "else": {"type": "var", "name": "patch"}
           }
         ]
       , [ "inputs"
         , { "type": "map_union"
           , "$1":
-            [{"type": "var", "name": "orig"}, {"type": "var", "name": "patch"}]
+            [ {"type": "var", "name": "orig"}
+            , {"type": "var", "name": "patch"}
+            , {"type": "var", "name": "TOOLCHAIN"}
+            , {"type": "var", "name": "script"}
+            ]
           }
         ]
       , [ "patched"
         , { "type": "ACTION"
           , "inputs": {"type": "var", "name": "inputs"}
           , "outs": ["patched"]
-          , "cmd":
-            [ {"type": "var", "name": "PATCH", "default": "patch"}
-            , "-s"
-            , "--read-only=ignore"
-            , "--follow-symlinks"
-            , "-o"
-            , "patched"
-            , "orig"
-            , "patch"
-            ]
+          , "cmd": ["sh", "./run_patch.sh"]
+          , "env": {"type": "var", "name": "ENV"}
           }
         ]
       , [ "result"
diff --git a/patch/TARGETS b/patch/TARGETS
new file mode 100644
index 0000000..9a0ad77
--- /dev/null
+++ b/patch/TARGETS
@@ -0,0 +1,6 @@
+{ "defaults":
+  { "type": ["patch", "defaults"]
+  , "PATCH": ["patch"]
+  , "PATH": ["/bin", "/usr/bin"]
+  }
+}
diff --git a/transitions/EXPRESSIONS b/transitions/EXPRESSIONS
index db401a0..fef8542 100644
--- a/transitions/EXPRESSIONS
+++ b/transitions/EXPRESSIONS
@@ -1,13 +1,22 @@
 { "for host":
-  { "vars": ["ARCH", "HOST_ARCH"]
+  { "vars": ["ARCH", "HOST_ARCH", "TARGET_ARCH"]
   , "expression":
-    { "type": "singleton_map"
-    , "key": "TARGET_ARCH"
-    , "value":
-      { "type": "var"
-      , "name": "HOST_ARCH"
-      , "default": {"type": "var", "name": "ARCH"}
-      }
+    { "type": "let*"
+    , "bindings":
+      [ [ "BUILD_ARCH"
+        , { "type": "var"
+          , "name": "TARGET_ARCH"
+          , "default": {"type": "var", "name": "ARCH"}
+          }
+        ]
+      , [ "TARGET_ARCH"
+        , { "type": "var"
+          , "name": "HOST_ARCH"
+          , "default": {"type": "var", "name": "ARCH"}
+          }
+        ]
+      ]
+    , "body": {"type": "env", "vars": ["BUILD_ARCH", "TARGET_ARCH"]}
     }
   }
 , "with fPIC":