foreign: Implement 'expand_exec' via POSIX shell

... and coreutils by default. This has the advantage that no
C compiler and no specific toolchain definition is required
to build rule-internal tools. 'expand_exec' is provided via
an implicit target with proper config transition for host,
so it could be overwritten by the rule user. The C code of
the previous implementation is still kept as an example.

2 files changed, 24 insertions, 17 deletions

diff --git a/CC/foreign/make/EXPRESSIONS b/CC/foreign/make/EXPRESSIONS
index aeafbfc..ceb5913 100644
--- a/CC/foreign/make/EXPRESSIONS
+++ b/CC/foreign/make/EXPRESSIONS
@@ -25,7 +25,7 @@
     , "BUILD_POSITION_INDEPENDENT"
     , "TIMEOUT_SCALE"
     , "defaults-transition"
-    , "host-defaults-transition"
+    , "expand_exec"
     ]
   , "imports":
     { "artifacts": ["", "field_artifacts"]
@@ -40,7 +40,6 @@
     , "default-PATH": ["CC", "default-PATH"]
     , "default-TOOLCHAIN": ["CC", "default-TOOLCHAIN"]
     , "default-NON_SYSTEM_TOOLS": ["CC", "default-NON_SYSTEM_TOOLS"]
-    , "expand_exec_tool": ["./", "..", "expand_exec_tool"]
     , "foreign-MAKE": ["CC/foreign", "default-MAKE"]
     , "foreign-ENV": ["CC/foreign", "default-ENV"]
     , "foreign-PATH": ["CC/foreign", "default-PATH"]
@@ -50,17 +49,7 @@
   , "expression":
     { "type": "let*"
     , "bindings":
-      [ [ "expand_exec"
-        , { "type": "let*"
-          , "bindings":
-            [ [ "defaults-transition"
-              , {"type": "var", "name": "host-defaults-transition"}
-              ]
-            ]
-          , "body": {"type": "CALL_EXPRESSION", "name": "expand_exec_tool"}
-          }
-        ]
-      , ["TOOLCHAIN_DIR", "toolchain"]
+      [ ["TOOLCHAIN_DIR", "toolchain"]
       , [ "TOOLCHAIN"
         , { "type": "disjoint_map_union"
           , "msg": "Toolchain trees may not overlap"
diff --git a/CC/foreign/make/RULES b/CC/foreign/make/RULES
index 08e5414..76fca18 100644
--- a/CC/foreign/make/RULES
+++ b/CC/foreign/make/RULES
@@ -41,6 +41,7 @@
   , "implicit":
     { "defaults": [["CC", "defaults"]]
     , "foreign-defaults": [["CC/foreign", "defaults"]]
+    , "expand_exec": [["./", "..", "expand_exec"]]
     }
   , "field_doc":
     { "project":
@@ -172,6 +173,7 @@
   , "config_transitions":
     { "defaults":
       [{"type": "empty_map"}, {"type": "CALL_EXPRESSION", "name": "for host"}]
+    , "expand_exec": [{"type": "CALL_EXPRESSION", "name": "for host"}]
     }
   , "expression":
     { "type": "let*"
@@ -221,8 +223,15 @@
       , ["pre_cmds", {"type": "FIELD", "name": "pre_cmds"}]
       , ["post_cmds", {"type": "FIELD", "name": "post_cmds"}]
       , ["defaults-transition", {"type": "empty_map"}]
-      , [ "host-defaults-transition"
-        , {"type": "CALL_EXPRESSION", "name": "for host"}
+      , [ "expand_exec"
+        , { "type": "let*"
+          , "bindings":
+            [ ["fieldname", "expand_exec"]
+            , ["location", "expand_exec"]
+            , ["transition", {"type": "CALL_EXPRESSION", "name": "for host"}]
+            ]
+          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
+          }
         ]
       , ["full_install_dir", {"type": "CALL_EXPRESSION", "name": "make-build"}]
       , [ "install_dir"
@@ -323,6 +332,7 @@
     { "defaults": [["CC", "defaults"]]
     , "foreign-defaults": [["CC/foreign", "defaults"]]
     , "config_reader": [["CC", "prebuilt/read_pkgconfig.py"]]
+    , "expand_exec": [["./", "..", "expand_exec"]]
     }
   , "field_doc":
     { "project":
@@ -492,6 +502,7 @@
   , "config_transitions":
     { "defaults":
       [{"type": "empty_map"}, {"type": "CALL_EXPRESSION", "name": "for host"}]
+    , "expand_exec": [{"type": "CALL_EXPRESSION", "name": "for host"}]
     }
   , "expression":
     { "type": "let*"
@@ -630,8 +641,15 @@
       , ["pre_cmds", {"type": "FIELD", "name": "pre_cmds"}]
       , ["post_cmds", {"type": "FIELD", "name": "post_cmds"}]
       , ["defaults-transition", {"type": "empty_map"}]
-      , [ "host-defaults-transition"
-        , {"type": "CALL_EXPRESSION", "name": "for host"}
+      , [ "expand_exec"
+        , { "type": "let*"
+          , "bindings":
+            [ ["fieldname", "expand_exec"]
+            , ["location", "expand_exec"]
+            , ["transition", {"type": "CALL_EXPRESSION", "name": "for host"}]
+            ]
+          , "body": {"type": "CALL_EXPRESSION", "name": "stage_field"}
+          }
         ]
       , ["full_install_dir", {"type": "CALL_EXPRESSION", "name": "make-build"}]
       , [ "install_dir"