error on user pragma args (#21776)

closes #20978

compiler/pragmas.nim

@@ -826,7 +826,8 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
                   validPragmas: TSpecialWords,
                   comesFromPush, isStatement: bool): bool =
   var it = n[i]
-  var key = if it.kind in nkPragmaCallKinds and it.len > 1: it[0] else: it
+  let keyDeep = it.kind in nkPragmaCallKinds and it.len > 1
+  var key = if keyDeep: it[0] else: it
   if key.kind == nkBracketExpr:
     processNote(c, it)
     return
@@ -852,6 +853,9 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
     if c.instCounter > 100:
       globalError(c.config, it.info, "recursive dependency: " & userPragma.name.s)
 
+    if keyDeep:
+      localError(c.config, it.info, "user pragma cannot have arguments")
+
     pragma(c, sym, userPragma.ast, validPragmas, isStatement)
     n.sons[i..i] = userPragma.ast.sons # expand user pragma with its content
     i.inc(userPragma.ast.len - 1) # inc by -1 is ok, user pragmas was empty

tests/pragmas/tuserpragmaargs.nim

@@ -0,0 +1,5 @@
+var foo {.exportc: "abc".} = 123
+{.pragma: importc2, importc.}
+var bar {.importc2: "abc".}: int #[tt.Error
+                  ^ user pragma cannot have arguments]#
+echo bar