New/better macro pragmas, mark some as experimental (#19406)

* New/better macro pragmas, make some experimental

fix #15920, close #18212, close #14781, close #6696,
close https://github.com/nim-lang/RFCs/issues/220

Variable macro pragmas have been changed to
only take a unary section node.
They can now also be applied in sections with multiple variables,
as well as `const` sections. They also accept arguments.

Templates now support macro pragmas, mirroring other routine types.

Type and variable macro pragmas have been made experimental.
Symbols without parentheses instatiating nullary macros or templates
has also been documented in the experimental manual.

A check for a redefinition error based on the left hand side of variable
definitions when using variable macro pragmas was disabled.
This nerfs `byaddr` specifically, however this has been documented as
a consequence of the experimental features `byaddr` uses.

Given how simple these changes are I'm worried if I'm missing something.

* accomodate compiler boot

* allow weird pragmas

* add test for #10994

* remove some control flow, try remove some logic

1 files changed, 12 insertions, 54 deletions

diff --git a/tests/stdlib/tdecls.nim b/tests/stdlib/tdecls.nim
index c0d6f8a08..4e7407045 100644
--- a/tests/stdlib/tdecls.nim
+++ b/tests/stdlib/tdecls.nim
@@ -13,15 +13,18 @@ template fun() =
   var b {.byaddr.}: int = s[0]
   doAssert a.addr == b.addr
 
-  doAssert not compiles(block:
-    # redeclaration not allowed
-    var foo = 0
-    var foo {.byaddr.} = s[0])
-
-  doAssert not compiles(block:
-    # ditto
-    var foo {.byaddr.} = s[0]
-    var foo {.byaddr.} = s[0])
+  when false:
+    # template specific redeclaration issue
+    # see https://github.com/nim-lang/Nim/issues/8275
+    doAssert not compiles(block:
+      # redeclaration not allowed
+      var foo = 0
+      var foo {.byaddr.} = s[0])
+
+    doAssert not compiles(block:
+      # ditto
+      var foo {.byaddr.} = s[0]
+      var foo {.byaddr.} = s[0])
 
   block:
     var b {.byaddr.} = s[1] # redeclaration ok in sub scope
@@ -44,48 +47,3 @@ fun2()
 static: fun2()
 when false: # pending bug #13887
   static: fun()
-
-## We can define custom pragmas in user code
-template byUnsafeAddr(lhs, typ, expr) =
-  when typ is type(nil):
-    let tmp = addr(expr)
-  else:
-    let tmp: ptr typ = addr(expr)
-  template lhs: untyped = tmp[]
-
-block:
-  let s = @["foo", "bar"]
-  let a {.byUnsafeAddr.} = s[0]
-  doAssert a == "foo"
-  doAssert a[0].addr == s[0][0].addr
-
-block: # nkAccQuoted
-  # shows using a keyword, which requires nkAccQuoted
-  template `cast`(lhs, typ, expr) =
-    when typ is type(nil):
-      let tmp = addr(expr)
-    else:
-      let tmp: ptr typ = addr(expr)
-    template lhs: untyped = tmp[]
-
-  block:
-    let s = @["foo", "bar"]
-    let a {.`byUnsafeAddr`.} = s[0]
-    doAssert a == "foo"
-    doAssert a[0].addr == s[0][0].addr
-
-  block:
-    let s = @["foo", "bar"]
-    let a {.`cast`.} = s[0]
-    doAssert a == "foo"
-    doAssert a[0].addr == s[0][0].addr
-
-block: # bug #15920
-  template foo(lhs, typ, expr) =
-    let lhs = expr
-  proc fun1()=
-    let a {.foo.} = 1
-  template fun2()=
-    let a {.foo.} = 1
-  fun1() # ok
-  fun2() # BUG