cps, cps/environment: only desym environment fields (#73)

* cps, cps/environment: only desym environment access

This is a WIP commit.

Experiments shows that we only have to desym due to issues in
environment definition and access.

Upstream bug: nim-lang/Nim#17851

This commit disable blanket desymification and only perform them
on environment as a workaround for the mentioned bug, which fixes
the foreign symbol tests.

* cps: disable blanket desym with comments

* cps: nicer getCallSym interface

* cps/environment: don't desym Env type

The better fix in #72 removed the need for this 🎉.

* cps/[environment, spec]: added genField for generating object fields

A proper workaround for nim-lang/Nim#17851,
which lets us remove the desym injections into cps/environment.

* cps: cater getCallSym to reviews

* cps/spec: English is hard

cps.nim

@@ -28,6 +28,7 @@ when defined(yourdaywillcomelittleonecommayourdaywillcomedotdotdot):
 
 func getCallSym(n: NimNode): NimNode =
   ## Get the symbol that is being called
+  ## Returns nil if there is no symbol
   expectKind n, callish
   result = n[0]
   while result != nil:
@@ -37,18 +38,18 @@ func getCallSym(n: NimNode): NimNode =
     of nnkSym:
       break
     of nnkIdent:
-      raise newException(CatchableError, "This call is not typed")
+      result = nil
     else:
-      assert false, "unknown node type: " & $result.kind
-  assert not result.isNil
+      raise newException(Defect, "unknown node type: " & $result.kind)
 
 proc isCpsCall(n: NimNode): bool =
   ## true if this node holds a call to a cps procedure
   assert not n.isNil
   if len(n) > 0:
     if n.kind in callish:
-      let p = n.getCallSym.getImpl
-      result = p.hasPragma("cpsCall")
+      let callee = n.getCallSym
+      if not callee.isNil:
+        result = callee.getImpl.hasPragma("cpsCall")
 
 proc firstReturn(p: NimNode): NimNode =
   ## find the first return statement within statement lists, or nil
@@ -808,9 +809,11 @@ proc cpsXfrmProc(T: NimNode, n: NimNode): NimNode =
   env = env.storeType(force = off)
 
   # Araq: "learn how to desemantic your ast, knuckleheads"
-  n.body = replacedSymsWithIdents(n.body)
-  types = replacedSymsWithIdents(types)
-  booty = replacedSymsWithIdents(booty)
+  # No longer necessary as we are desym-ing on a selective basis
+  when false:
+    n.body = replacedSymsWithIdents(n.body)
+    types = replacedSymsWithIdents(types)
+    booty = replacedSymsWithIdents(booty)
 
   # lifting the generated proc bodies
   result = lambdaLift(types, n)

cps/environment.nim

@@ -38,7 +38,7 @@ type
     fn: NimNode                     # the sym we use for the goto target
     ex: NimNode                     # the sym we use for stored exception
     rs: NimNode                     # the sym we use for "yielded" result
-  
+
 func insideCps*(e: Env): bool = len(e.gotos) > 0 or len(e.breaks) > 0
 
 template searchScope(env: Env; x: untyped;
@@ -204,13 +204,13 @@ proc init(e: var Env) =
   e.seen = initHashSet[string]()
   if e.fn.isNil:
     when cpsFn:
-      e.fn = genSym(nskField, "fn")
+      e.fn = genField("fn")
     else:
       e.fn = ident"fn"
   if e.ex.isNil:
-    e.ex = genSym(nskField, "ex")
+    e.ex = genField("ex")
   if e.rs.isNil:
-    e.rs = genSym(nskField, "result")
+    e.rs = genField("result")
   e.id = genSym(nskType, "env")
 
 proc allPairs(e: Env): seq[Pair] =
@@ -393,7 +393,7 @@ iterator addIdentDef(e: var Env; kind: NimNodeKind; n: NimNode): Pair =
       # iterate over the identifier names (a, b, c)
       for name in n[0 ..< len(n)-2]:  # ie. omit (:type) and (=default)
         # create a new identifier for the object field
-        let field = genSym(nskField, name.strVal)
+        let field = genField(name.strVal)
         let value = newTree(kind,     # ident: <no var> type = default
                             newIdentDefs(name, stripVar(n[^2]), n[^1]))
         e = e.set(field, value)
@@ -404,7 +404,7 @@ iterator addIdentDef(e: var Env; kind: NimNodeKind; n: NimNode): Pair =
     let tup = n.last
     for i in 0 ..< len(tup):
       let name = n[i]
-      let field = genSym(nskField, name.strVal)
+      let field = genField(name.strVal)
       let value = newTree(kind,
                           newIdentDefs(name, getTypeInst(tup[i]), tup[i]))
       e = e.set(field, value)

cps/spec.nim

@@ -275,3 +275,9 @@ proc errorAst*(s: string): NimNode =
 proc errorAst*(n: NimNode; s = "creepy ast"): NimNode =
   ## embed an error with a message
   errorAst s & ":\n" & treeRepr(n) & "\n"
+
+proc genField*(ident = ""): NimNode =
+  ## generate a unique field to put inside an object definition
+  ##
+  ## made as a workaround for [nim-lang/Nim#17851](https://github.com/nim-lang/Nim/issues/17851)
+  desym genSym(nskField, ident)

tests/taste.nim

@@ -588,35 +588,29 @@ testes:
 
   block:
     ## call a macro that calls a foreign symbol
-    when true:
-      skip "not working yet, see #53"
-    else:
-      r = 0
-      proc foo() {.cps: Cont.} =
-        inc r
-        let i = 42
-        noop()
-        inc r
-        check jsonifyImplicit(i) == $i
+    r = 0
+    proc foo() {.cps: Cont.} =
+      inc r
+      let i = 42
+      noop()
+      inc r
+      check jsonifyImplicit(i) == $i
 
-      trampoline foo()
-      check r == 2
+    trampoline foo()
+    check r == 2
 
   block:
     ## call a template with explicit bind
-    when true:
-      skip "not working yet, see #53"
-    else:
-      r = 0
-      proc foo() {.cps: Cont.} =
-        inc r
-        let i = 42
-        noop()
-        inc r
-        check jsonifyBind(i) == $i
+    r = 0
+    proc foo() {.cps: Cont.} =
+      inc r
+      let i = 42
+      noop()
+      inc r
+      check jsonifyBind(i) == $i
 
-      trampoline foo()
-      check r == 2
+    trampoline foo()
+    check r == 2
 
   block:
     ## template call in nested call nodes