Better support for treating templates and macros as symbols.

This allows you to pass a template or a macro to another macro
which can then inspect the implementation of the former template/macro
using `getImpl`.

Since templates can be freely redefined, this allows you to treat
their symbols as compile-time variables that have lexical scope.
A motivating PoC example for a logging library taking advantage of
this will be provided in the next commit.

Implementation details:

* The name of a template or a macro will be consider a symbol if
  the template/macro requires parameters

* For parameterless templates/macros, you can use `bindSym`, which
  was extended to also work outside of compile-time procs.

compiler/ast.nim

@@ -1615,6 +1615,19 @@ proc originatingModule*(s: PSym): PSym =
 proc isRoutine*(s: PSym): bool {.inline.} =
   result = s.kind in skProcKinds
 
+proc isCompileTimeProc*(s: PSym): bool {.inline.} =
+  result = s.kind == skMacro or
+           s.kind == skProc and sfCompileTime in s.flags
+
+proc requiredParams*(s: PSym): int =
+  # Returns the number of required params (without default values)
+  # XXX: Perhaps we can store this in the `offset` field of the
+  # symbol instead?
+  for i in 1 ..< s.typ.len:
+    if s.typ.n[i].sym.ast != nil:
+      return i - 1
+  return s.typ.len - 1
+
 proc hasPattern*(s: PSym): bool {.inline.} =
   result = isRoutine(s) and s.ast.sons[patternPos].kind != nkEmpty
 

compiler/evaltempl.nim

@@ -63,7 +63,7 @@ proc evalTemplateArgs(n: PNode, s: PSym; fromHlo: bool): PNode =
   # if the template has zero arguments, it can be called without ``()``
   # `n` is then a nkSym or something similar
   var totalParams = case n.kind
-    of nkCall, nkInfix, nkPrefix, nkPostfix, nkCommand, nkCallStrLit: n.len-1
+    of nkCallKinds: n.len-1
     else: 0
 
   var

compiler/semexprs.nim

@@ -960,18 +960,20 @@ proc semSym(c: PContext, n: PNode, sym: PSym, flags: TExprFlags): PNode =
     else:
       result = newSymNode(s, n.info)
   of skMacro:
-    if efNoEvaluateGeneric in flags and s.ast[genericParamsPos].len > 0:
+    if efNoEvaluateGeneric in flags and s.ast[genericParamsPos].len > 0 or
+       (n.kind notin nkCallKinds and s.requiredParams > 0):
       markUsed(n.info, s, c.graph.usageSym)
       styleCheckUse(n.info, s)
-      result = newSymNode(s, n.info)
+      result = symChoice(c, n, s, scClosed)
     else:
       result = semMacroExpr(c, n, n, s, flags)
   of skTemplate:
     if efNoEvaluateGeneric in flags and s.ast[genericParamsPos].len > 0 or
+       (n.kind notin nkCallKinds and s.requiredParams > 0) or
        sfCustomPragma in sym.flags:
       markUsed(n.info, s, c.graph.usageSym)
       styleCheckUse(n.info, s)
-      result = newSymNode(s, n.info)
+      result = symChoice(c, n, s, scClosed)
     else:
       result = semTemplateExpr(c, n, s, flags)
   of skParam:

compiler/semmagic.nim

@@ -199,6 +199,10 @@ proc semBindSym(c: PContext, n: PNode): PNode =
   if s != nil:
     # we need to mark all symbols:
     var sc = symChoice(c, id, s, TSymChoiceRule(isMixin.intVal))
+    if not getCurrOwner(c).isCompileTimeProc:
+      # inside regular code, bindSym resolves to the sym-choice
+      # nodes (see tinspectsymbol)
+      return sc
     result.add(sc)
   else:
     errorUndeclaredIdentifier(c, n.sons[1].info, sl.strVal)

compiler/sigmatch.nim

@@ -2032,8 +2032,9 @@ proc paramTypesMatch*(m: var TCandidate, f, a: PType,
     y.calleeSym = m.calleeSym
     z.calleeSym = m.calleeSym
     var best = -1
-    for i in countup(0, sonsLen(arg) - 1):
-      if arg.sons[i].sym.kind in {skProc, skFunc, skMethod, skConverter, skIterator}:
+    for i in 0 ..< arg.len:
+      if arg.sons[i].sym.kind in {skProc, skFunc, skMethod, skConverter,
+                                  skIterator, skMacro, skTemplate}:
         copyCandidate(z, m)
         z.callee = arg.sons[i].typ
         if tfUnresolved in z.callee.flags: continue
@@ -2062,6 +2063,7 @@ proc paramTypesMatch*(m: var TCandidate, f, a: PType,
               x = z
             elif cmp == 0:
               y = z           # z is as good as x
+
     if x.state == csEmpty:
       result = nil
     elif y.state == csMatch and cmpCandidates(x, y) == 0:
@@ -2070,7 +2072,7 @@ proc paramTypesMatch*(m: var TCandidate, f, a: PType,
       # ambiguous: more than one symbol fits!
       # See tsymchoice_for_expr as an example. 'f.kind == tyExpr' should match
       # anyway:
-      if f.kind == tyExpr: result = arg
+      if f.kind in {tyExpr, tyStmt}: result = arg
       else: result = nil
     else:
       # only one valid interpretation found: