allows access to .compileTime vars at runtime (#12128)

compiler/ccgexprs.nim

@@ -2533,6 +2533,9 @@ proc expr(p: BProc, n: PNode, d: var TLoc) =
     of skVar, skForVar, skResult, skLet:
       if {sfGlobal, sfThread} * sym.flags != {}:
         genVarPrototype(p.module, n)
+        if sfCompileTime in sym.flags:
+          genSingleVar(p, sym, n, astdef(sym))
+
       if sym.loc.r == nil or sym.loc.t == nil:
         #echo "FAILED FOR PRCO ", p.prc.name.s
         #echo renderTree(p.prc.ast, {renderIds})

compiler/ccgstmts.nim

@@ -271,19 +271,16 @@ proc genGotoVar(p: BProc; value: PNode) =
   else:
     lineF(p, cpsStmts, "goto NIMSTATE_$#;$n", [value.intVal.rope])
 
-proc genSingleVar(p: BProc, a: PNode) =
+proc genSingleVar(p: BProc, v: PSym; vn, value: PNode) =
-  let vn = a.sons[0]
-  let v = vn.sym
-  if sfCompileTime in v.flags: return
   if sfGoto in v.flags:
     # translate 'var state {.goto.} = X' into 'goto LX':
-    genGotoVar(p, a.sons[2])
+    genGotoVar(p, value)
     return
   var targetProc = p
   var traverseProc: Rope
   if sfGlobal in v.flags:
     if v.flags * {sfImportc, sfExportc} == {sfImportc} and
-        a.sons[2].kind == nkEmpty and
+        value.kind == nkEmpty and
         v.loc.flags * {lfHeader, lfNoDecl} != {}:
       return
     if sfPure in v.flags:
@@ -313,14 +310,13 @@ proc genSingleVar(p: BProc, a: PNode) =
     if traverseProc != nil and not p.hcrOn:
       registerTraverseProc(p, v, traverseProc)
   else:
-    let value = a.sons[2]
     let imm = isAssignedImmediately(p.config, value)
     if imm and p.module.compileToCpp and p.splitDecls == 0 and
         not containsHiddenPointer(v.typ):
       # C++ really doesn't like things like 'Foo f; f = x' as that invokes a
       # parameterless constructor followed by an assignment operator. So we
       # generate better code here: 'Foo f = x;'
-      genLineDir(p, a)
+      genLineDir(p, vn)
       let decl = localVarDecl(p, vn)
       var tmp: TLoc
       if value.kind in nkCallKinds and value[0].kind == nkSym and
@@ -363,12 +359,17 @@ proc genSingleVar(p: BProc, a: PNode) =
     lineCg(targetProc, cpsStmts, "if (hcrRegisterGlobal($3, \"$1\", sizeof($2), $4, (void**)&$1))$N",
            [v.loc.r, rdLoc(v.loc), getModuleDllPath(p.module, v), traverseProc])
     startBlock(targetProc)
-  if a.sons[2].kind != nkEmpty:
+  if value.kind != nkEmpty:
-    genLineDir(targetProc, a)
+    genLineDir(targetProc, vn)
-    loadInto(targetProc, a.sons[0], a.sons[2], v.loc)
+    loadInto(targetProc, vn, value, v.loc)
   if forHcr:
     endBlock(targetProc)
 
+proc genSingleVar(p: BProc, a: PNode) =
+  let v = a[0].sym
+  if sfCompileTime in v.flags: return
+  genSingleVar(p, v, a[0], a.sons[2])
+
 proc genClosureVar(p: BProc, a: PNode) =
   var immediateAsgn = a.sons[2].kind != nkEmpty
   var v: TLoc

compiler/pragmas.nim

@@ -839,7 +839,7 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
       of wCompileTime:
         noVal(c, it)
         incl(sym.flags, sfCompileTime)
-        incl(sym.loc.flags, lfNoDecl)
+        #incl(sym.loc.flags, lfNoDecl)
       of wGlobal:
         noVal(c, it)
         incl(sym.flags, sfGlobal)
@@ -1131,7 +1131,7 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
     elif comesFromPush and whichKeyword(ident) in {wTags, wRaises}:
       discard "ignore the .push pragma; it doesn't apply"
     else:
-      if sym == nil or (sym != nil and sym.kind in {skVar, skLet, skParam,
+      if sym == nil or (sym.kind in {skVar, skLet, skParam,
                         skField, skProc, skFunc, skConverter, skMethod, skType}):
         n.sons[i] = semCustomPragma(c, it)
       elif sym != nil:

doc/manual.rst

@@ -5928,6 +5928,31 @@ Is the same as:
   proc astHelper(n: NimNode): NimNode {.compileTime.} =
     result = n
 
+``compileTime`` variables are available at runtime too. This simplifies certain
+idioms where variables are filled at compile-time (for example, lookup tables)
+but accessed at runtime:
+
+.. code-block:: nim
+    :test: "nim c -r $1"
+
+  import macros
+
+  var nameToProc {.compileTime.}: seq[(string, proc (): string {.nimcall.})]
+
+  macro registerProc(p: untyped): untyped =
+    result = newTree(nnkStmtList, p)
+
+    let procName = p[0]
+    let procNameAsStr = $p[0]
+    result.add quote do:
+      nameToProc.add((`procNameAsStr`, `procName`))
+
+  proc foo: string {.registerProc.} = "foo"
+  proc bar: string {.registerProc.} = "bar"
+  proc baz: string {.registerProc.} = "baz"
+
+  doAssert nameToProc[2][1]() == "baz"
+
 
 noReturn pragma
 ---------------

tests/vm/tcompiletimetable.nim

@@ -3,7 +3,10 @@ discard """
 3
 4:2
 Got Hi
-Got Hey'''
+Got Hey
+a
+b
+c'''
 """
 
 # bug #404
@@ -47,3 +50,9 @@ addStuff("Hey"): echo "Hey"
 addStuff("Hi"): echo "Hi"
 dump()
 
+# ensure .compileTime vars can be used at runtime:
+import macros
+
+var xzzzz {.compileTime.}: array[3, string] = ["a", "b", "c"]
+
+for i in 0..high(xzzzz): echo xzzzz[i]