process non-language pragma nodes in templates (#24183)

fixes #24186 

When encountering pragma nodes in templates, if it's a language pragma,
we don't process the name, and only any values if they exist. If it's
not a language pragma, we process the full node. Previously only the
values of colon expressions were processed.

To make this simpler, `whichPragma` is patched to consider bracketed
hint/warning etc pragmas like `{.hint[HintName]: off.}` as being a
pragma of kind `wHint` rather than an invalid pragma which would have to
be checked separately. From looking at the uses of `whichPragma` this
doesn't seem like it would cause problems.

Generics have [the same
problem](https://github.com/nim-lang/Nim/blob/a27542195c9ba760d58e9d1e977313bc322a1ede/compiler/semgnrc.nim#L619)
(causing #18649), but to make it work we need to make sure the
templates/macros don't get evaluated or get evaluated correctly (i.e.
passing the proc node as the final argument), either with #23094 or by
completely disabling template/macro evaluation when processing the
pragma node, which would also cover `{.pragma.}` templates.

compiler/semtempl.nim

@@ -535,13 +535,20 @@ proc semTemplBody(c: var TemplCtx, n: PNode): PNode =
   of nkConverterDef:
     result = semRoutineInTemplBody(c, n, skConverter)
   of nkPragmaExpr:
-    result[0] = semTemplBody(c, n[0])
+    result = semTemplBodySons(c, n)
   of nkPostfix:
     result[1] = semTemplBody(c, n[1])
   of nkPragma:
-    for x in n:
-      if x.kind == nkExprColonExpr:
-        x[1] = semTemplBody(c, x[1])
+    for i in 0 ..< n.len:
+      let x = n[i]
+      let prag = whichPragma(x)
+      if prag == wInvalid:
+        # only sem if not a language-level pragma 
+        result[i] = semTemplBody(c, x)
+      elif x.kind in nkPragmaCallKinds:
+        # is pragma, but value still needs to be checked
+        for j in 1 ..< x.len:
+          x[j] = semTemplBody(c, x[j])
   of nkBracketExpr:
     if n.typ == nil:
       # if a[b] is nested inside a typed expression, don't convert it

compiler/trees.nim

@@ -147,6 +147,13 @@ proc whichPragma*(n: PNode): TSpecialWord =
   of nkCast: return wCast
   of nkClosedSymChoice, nkOpenSymChoice:
     return whichPragma(key[0])
+  of nkBracketExpr:
+    if n.kind notin nkPragmaCallKinds: return wInvalid
+    result = whichPragma(key[0])
+    if result notin {wHint, wHintAsError, wWarning, wWarningAsError}:
+      # note bracket pragmas, see processNote
+      result = wInvalid
+    return
   else: return wInvalid
   if result in nonPragmaWordsLow..nonPragmaWordsHigh:
     result = wInvalid

tests/template/tpragma.nim

@@ -0,0 +1,28 @@
+# issue #24186
+
+macro mymacro(typ: typedesc; def) =
+  def
+
+macro mymacro2(typ: typedesc; typ2: typedesc; def) =
+  def
+
+template mytemplate(typ: typedesc) =   # works
+  proc myproc() {.mymacro: typ .} =
+    discard
+
+template mytemplate2(typ: typedesc) =   # Error: undeclared identifier: 'typ'
+  proc myproc2() {.mymacro(typ) .} =
+    discard
+
+template mytemplate3(typ: typedesc, typ2: typedesc) =  # Error: undeclared identifier: 'typ'
+  proc myproc3() {.mymacro2(typ, typ2) .} =
+    discard
+
+template mytemplate4() =  # works
+  proc myproc4() {.mymacro2(string, int) .} =
+    discard
+
+mytemplate(string)
+mytemplate2(string)
+mytemplate3(string, int)
+mytemplate4()