rules: Refactoring and minor improvements

Compared to the previous commit, the action graphs for just
and its unit tests are unchanged.
- Git hash of action graph for ["",""]:
    c6e75f17abd7ffaab6ff9bb725ad67ec0bf6c973
- Git hash of action graph for ["test/buildtool","TESTS"]:
    8063dfb3dd7daa9ae01d95c177e14946f785c57e

Refactor:
- "local cflags" to "private-cflags"
- "local defines" to "private-defines"
- "link externals" to "private-ldflags"
- "deps" to "private-deps" for (test) binaries
- "proto" to "private-proto" for binaries

Improvements:
- consistent variable declaration order:
    OS, ARCH, HOST_ARCH, TARGET_ARCH,
    CC, CXX, CFLAGS, CXXFLAGS, ADD_CFLAGS, ADD_CXXFLAGS,
    AR, ENV, PATH
- use fields close to their definition (in RULES)
- use common expression for binaries and test binaries
- split expression "flags" and "compiler"
  ... to separate ones for CC and CXX.
- rename "transition" to "deps-transition"
  ... to avoid conflicts with other transitions.
- support "defaults-transition" for CC expressions

Implement:
- "cflags" for libraries
- "private-cflags" for (test) binaries
- "private-defines" for test binaries
- "private-ldflags" for test binaries
- (public) "defines" for libraries

2 files changed, 23 insertions, 9 deletions

diff --git a/shell/test/EXPRESSIONS b/shell/test/EXPRESSIONS
index 24bf9ec..444de92 100644
--- a/shell/test/EXPRESSIONS
+++ b/shell/test/EXPRESSIONS
@@ -1,5 +1,13 @@
 { "test-action":
-  { "vars": ["name", "test.sh", "ATTEMPT", "TEST_ENV"]
+  { "vars":
+    [ "TEST_ENV"
+    , "ATTEMPT"
+    , "name"
+    , "test.sh"
+    , "keep"
+    , "runner"
+    , "deps-fieldname"
+    ]
   , "imports":
     { "artifacts_list": ["./", "../..", "field_artifacts_list"]
     , "runfiles_list": ["./", "../..", "field_runfiles_list"]
@@ -12,7 +20,7 @@
           , "$1":
             { "type": "foreach"
             , "var": "runner"
-            , "range": {"type": "FIELD", "name": "runner"}
+            , "range": {"type": "var", "name": "runner"}
             , "body":
               { "type": "map_union"
               , "$1":
@@ -35,12 +43,17 @@
         , { "type": "TREE"
           , "$1":
             { "type": "disjoint_map_union"
-            , "msg": "Field 'deps' has to stage in a conflict free way"
+            , "msg":
+              [ "Field"
+              , {"type": "var", "name": "deps-fieldname"}
+              , "has to stage in a conflict free way"
+              ]
             , "$1":
               { "type": "++"
               , "$1":
                 { "type": "let*"
-                , "bindings": [["fieldname", "deps"]]
+                , "bindings":
+                  [["fieldname", {"type": "var", "name": "deps-fieldname"}]]
                 , "body":
                   [ {"type": "CALL_EXPRESSION", "name": "runfiles_list"}
                   , {"type": "CALL_EXPRESSION", "name": "artifacts_list"}
@@ -72,7 +85,7 @@
             [ ["result", "stdout", "stderr", "time-start", "time-stop"]
             , { "type": "foreach"
               , "var": "filename"
-              , "range": {"type": "FIELD", "name": "keep"}
+              , "range": {"type": "var", "name": "keep"}
               , "body":
                 { "type": "join"
                 , "$1": ["work/", {"type": "var", "name": "filename"}]
@@ -95,9 +108,7 @@
           }
         ]
       , [ "cmd"
-        , { "type": "++"
-          , "$1": [["./runner"], {"type": "FIELD", "name": "keep"}]
-          }
+        , {"type": "++", "$1": [["./runner"], {"type": "var", "name": "keep"}]}
         ]
       , [ "test_env"
         , {"type": "var", "name": "TEST_ENV", "default": {"type": "empty_map"}}
@@ -142,7 +153,7 @@
     }
   }
 , "test-result":
-  { "vars": ["name", "test.sh", "TEST_ENV"]
+  { "vars": ["TEST_ENV", "name", "test.sh", "keep", "runner", "deps-fieldname"]
   , "imports": {"action": "test-action"}
   , "expression":
     { "type": "let*"
diff --git a/shell/test/RULES b/shell/test/RULES
index 4242d94..990e8d9 100644
--- a/shell/test/RULES
+++ b/shell/test/RULES
@@ -75,6 +75,9 @@
           , "$1": {"type": "join", "$1": {"type": "FIELD", "name": "name"}}
           }
         ]
+      , ["keep", {"type": "FIELD", "name": "keep"}]
+      , ["runner", {"type": "FIELD", "name": "runner"}]
+      , ["deps-fieldname", "deps"]
       ]
     , "body":
       { "type": "if"