imports: Fix GRPC dependencies

... as the BUILD.bazel files that are the basis for the TARGETS
files seen to declare the dependencies in an incomplete way. Target
`grpc_base_c` needs `grpc_init()` and `grpc_shutdown()` from target
`grpc` (source `init.cc`). Adding this target dependency results
in a cycle.

This commit solves the issue by producing fewer but larger
libraries (as done in GRPC's CMakeLists.txt):
- `libgpr.a`: all gpr code
- `libgrpc.a`: all gprc code, depending on `libgpr.a`
- `libgrpc++.a`: all grpc++ code, depending on `libgrpc.a`

3 files changed, 235 insertions, 9 deletions

diff --git a/etc/import/RULES.grpc b/etc/import/RULES.grpc
new file mode 100644
index 00000000..195d3e25
--- /dev/null
+++ b/etc/import/RULES.grpc
@@ -0,0 +1,212 @@
+{ "combined lib":
+  { "doc": ["Combine multiple static libraries into a single one."]
+  , "target_fields": ["deps"]
+  , "string_fields": ["name", "stage"]
+  , "config_vars": ["AR", "ENV"]
+  , "implicit": {"defaults": [["@", "rules", "CC", "defaults"]]}
+  , "field_doc":
+    { "name":
+      ["The name of the library (without leading \"lib\" or trailing \".a\")."]
+    , "deps": ["All libraries (includes transitive) that should be combined."]
+    , "stage":
+      [ "The logical location of all public headers and the resulting library"
+      , "file. Individual directory components are joined with \"/\"."
+      ]
+    }
+  , "config_doc":
+    { "AR":
+      [ "The archive tool to used for creating the library. If None, the"
+      , "respective value from [\"@\", \"rules\", \"CC\", \"defaults\"] will"
+      , "be taken."
+      ]
+    , "ENV": ["The environment for any action generated."]
+    }
+  , "imports":
+    { "compile-deps": ["@", "rules", "CC", "compile-deps"]
+    , "compile-args-deps": ["@", "rules", "CC", "compile-args-deps"]
+    , "link-deps": ["@", "rules", "CC", "link-deps"]
+    , "link-args-deps": ["@", "rules", "CC", "link-args-deps"]
+    , "cflags-files-deps": ["@", "rules", "CC", "cflags-files-deps"]
+    , "ldflags-files-deps": ["@", "rules", "CC", "ldflags-files-deps"]
+    , "default-AR": ["@", "rules", "CC", "default-AR"]
+    }
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ [ "AR"
+        , { "type": "var"
+          , "name": "AR"
+          , "default": {"type": "CALL_EXPRESSION", "name": "default-AR"}
+          }
+        ]
+      , ["name", {"type": "join", "$1": {"type": "FIELD", "name": "name"}}]
+      , [ "stage"
+        , { "type": "join"
+          , "separator": "/"
+          , "$1": {"type": "FIELD", "name": "stage"}
+          }
+        ]
+      , [ "libname"
+        , { "type": "join"
+          , "$1": ["lib", {"type": "var", "name": "name"}, ".a"]
+          }
+        ]
+      , [ "libpath"
+        , { "type": "if"
+          , "cond": {"type": "var", "name": "stage"}
+          , "then":
+            { "type": "join"
+            , "separator": "/"
+            , "$1":
+              [ {"type": "var", "name": "stage"}
+              , {"type": "var", "name": "libname"}
+              ]
+            }
+          , "else": {"type": "var", "name": "libname"}
+          }
+        ]
+      , ["deps-fieldnames", ["deps"]]
+      , ["compile-deps", {"type": "CALL_EXPRESSION", "name": "compile-deps"}]
+      , [ "compile-args"
+        , {"type": "CALL_EXPRESSION", "name": "compile-args-deps"}
+        ]
+      , ["unstaged libs", {"type": "CALL_EXPRESSION", "name": "link-deps"}]
+      , [ "libs"
+        , { "type": "to_subdir"
+          , "subdir": "libs"
+          , "$1": {"type": "var", "name": "unstaged libs"}
+          }
+        ]
+      , ["link-deps", {"type": "empty_map"}]
+      , [ "link-args-deps"
+        , {"type": "CALL_EXPRESSION", "name": "link-args-deps"}
+        ]
+      , [ "non-lib-link-args-deps"
+        , { "type": "++"
+          , "$1":
+            { "type": "foreach"
+            , "var": "arg"
+            , "range": {"type": "var", "name": "link-args-deps"}
+            , "body":
+              { "type": "if"
+              , "cond":
+                { "type": "lookup"
+                , "map": {"type": "var", "name": "unstaged libs"}
+                , "key": {"type": "var", "name": "arg"}
+                }
+              , "then": []
+              , "else": [{"type": "var", "name": "arg"}]
+              }
+            }
+          }
+        ]
+      , [ "link-args"
+        , { "type": "++"
+          , "$1":
+            [ [{"type": "var", "name": "libpath"}]
+            , {"type": "var", "name": "non-lib-link-args-deps"}
+            ]
+          }
+        ]
+      , [ "ldflags-files"
+        , {"type": "CALL_EXPRESSION", "name": "ldflags-files-deps"}
+        ]
+      , [ "cflags-files"
+        , {"type": "CALL_EXPRESSION", "name": "cflags-files-deps"}
+        ]
+      , [ "package"
+        , { "type": "let*"
+          , "bindings": [["name", {"type": "var", "name": "name"}]]
+          , "body":
+            {"type": "env", "vars": ["name", "cflags-files", "ldflags-files"]}
+          }
+        ]
+      , [ "combine.sh"
+        , { "type": "singleton_map"
+          , "key": "combine.sh"
+          , "value":
+            { "type": "BLOB"
+            , "data":
+              { "type": "join"
+              , "separator": "\n"
+              , "$1":
+                [ "set -eu"
+                , "readonly ROOT=$(pwd)"
+                , "readonly AR=$1"
+                , "readonly OUT=$2"
+                , "shift 2"
+                , "for l in $@; do"
+                , "  OUTDIR=${ROOT}/objs/$l"
+                , "  mkdir -p $OUTDIR"
+                , "  cd $OUTDIR"
+                , "  $AR -t $ROOT/$l | sort | uniq -c | sed -e 's/^\\s*//' > obj.list"
+                , "  NUM=$(wc -l obj.list | cut -d' ' -f1)"
+                , "  for o in $(seq 1 $NUM); do"
+                , "    CNT=$(sed ''$o'q;d' obj.list | cut -d' ' -f1)"
+                , "    OBJ=$(sed ''$o'q;d' obj.list | cut -d' ' -f2)"
+                , "    for i in $(seq 1 $CNT); do"
+                , "      mkdir -p $i"
+                , "      $AR -xN $i $ROOT/$l $OBJ"
+                , "      mv *.o $i/"
+                , "    done"
+                , "  done"
+                , "  cd - >/dev/null"
+                , "  $AR -qc $OUT $OUTDIR/*/*.o"
+                , "done"
+                , "$AR s $OUT"
+                ]
+              }
+            }
+          }
+        ]
+      , [ "combined lib"
+        , { "type": "ACTION"
+          , "outs": [{"type": "var", "name": "libname"}]
+          , "inputs":
+            { "type": "disjoint_map_union"
+            , "$1":
+              [ {"type": "var", "name": "libs"}
+              , {"type": "var", "name": "combine.sh"}
+              ]
+            }
+          , "cmd":
+            { "type": "++"
+            , "$1":
+              [ [ "sh"
+                , "combine.sh"
+                , {"type": "var", "name": "AR"}
+                , {"type": "var", "name": "libname"}
+                ]
+              , {"type": "keys", "$1": {"type": "var", "name": "libs"}}
+              ]
+            }
+          , "env":
+            {"type": "var", "name": "ENV", "default": {"type": "empty_map"}}
+          }
+        ]
+      ]
+    , "body":
+      { "type": "RESULT"
+      , "artifacts": {"type": "var", "name": "combined lib"}
+      , "provides":
+        { "type": "map_union"
+        , "$1":
+          [ { "type": "env"
+            , "vars":
+              [ "compile-deps"
+              , "compile-args"
+              , "link-deps"
+              , "link-args"
+              , "package"
+              ]
+            }
+          , { "type": "var"
+            , "name": "extra-provides"
+            , "default": {"type": "empty_map"}
+            }
+          ]
+        }
+      }
+    }
+  }
+}
diff --git a/etc/import/TARGETS.grpc b/etc/import/TARGETS.grpc
index baadd06a..ce60ec3d 100644
--- a/etc/import/TARGETS.grpc
+++ b/etc/import/TARGETS.grpc
@@ -92,11 +92,13 @@
     , ["@", "absl", "absl/time", "time"]
     ]
   }
+, "gpr_combined":
+  {"type": "combined lib", "name": ["gpr"], "deps": ["gpr_base"]}
 , "gpr_internal":
   { "type": ["@", "rules", "CC", "library"]
   , "name": ["gpr"]
   , "hdrs": [["./", "include/grpc", "gpr_public_headers"]]
-  , "deps": ["gpr_base"]
+  , "deps": ["gpr_combined"]
   }
 , "atomic":
   { "type": ["@", "rules", "CC", "library"]
@@ -1416,9 +1418,9 @@
     , "grpc_server_backward_compatibility"
     ]
   }
-, "grpc_internal":
+, "grpc_main":
   { "type": ["@", "rules", "CC", "library"]
-  , "name": ["grpc"]
+  , "name": ["grpc_main"]
   , "srcs":
     [ "src/core/lib/surface/init.cc"
     , "src/core/plugin_registry/grpc_plugin_registry.cc"
@@ -1440,6 +1442,13 @@
     , "grpc_transport_chttp2_server_secure"
     ]
   }
+, "grpc_combined":
+  {"type": "combined lib", "name": ["grpc"], "deps": ["grpc_main"]}
+, "grpc_internal":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["grpc"]
+  , "deps": ["grpc_combined", "gpr"]
+  }
 , "grpc++_sources":
   { "type": ["@", "rules", "data", "staged"]
   , "srcs":
@@ -1541,9 +1550,9 @@
     , "grpc_health_upb"
     ]
   }
-, "grpc++internal":
+, "grpc++_main":
   { "type": ["@", "rules", "CC", "library"]
-  , "name": ["grpc++"]
+  , "name": ["grpc++_main"]
   , "srcs":
     [ "src/cpp/client/insecure_credentials.cc"
     , "src/cpp/client/secure_credentials.cc"
@@ -1564,15 +1573,19 @@
     , "src/cpp/server/secure_server_credentials.h"
     ]
   , "deps":
-    [ "gpr"
-    , "grpc"
-    , "grpc++_base"
+    [ "grpc++_base"
     , "grpc++_codegen_base"
     , "grpc++_codegen_base_src"
     , "grpc++_codegen_proto"
-    , "grpc_secure"
     ]
   }
+, "grpc++combined":
+  {"type": "combined lib", "name": ["grpc++"], "deps": ["grpc++_main"]}
+, "grpc++internal":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["grpc++"]
+  , "deps": ["grpc++combined", "grpc"]
+  }
 , "grpc++":
   { "type": "export"
   , "target": "grpc++internal"
diff --git a/etc/repos.json b/etc/repos.json
index a2ce0aca..f3dbad6e 100644
--- a/etc/repos.json
+++ b/etc/repos.json
@@ -366,6 +366,7 @@
       }
     , "target_root": "import targets"
     , "target_file_name": "TARGETS.grpc"
+    , "rule_file_name": "RULES.grpc"
     , "bindings":
       { "rules": "rules-grpc"
       , "protobuf": "protobuf"