Ensure that gc interface remains non-raising (#25006)

GC_fullCollect in particular has an annoying `Exception` effect

lib/system/arc.nim

@@ -14,6 +14,8 @@ at offset 0 then. The ``ref`` object header is independent from the
 runtime type and only contains a reference count.
 ]#
 
+{.push raises: [].}
+
 when defined(gcOrc):
   const
     rcIncrement = 0b10000 # so that lowest 4 bits are not touched
@@ -269,3 +271,5 @@ when defined(gcDestructors):
   proc nimGetVTable(p: pointer, index: int): pointer
         {.compilerRtl, inline, raises: [].} =
     result = cast[ptr PNimTypeV2](p).vTable[index]
+
+{.pop.} # raises: []

lib/system/cyclebreaker.nim

@@ -62,8 +62,8 @@ const
   colorMask = 0b011
 
 type
-  TraceProc = proc (p, env: pointer) {.nimcall, benign.}
-  DisposeProc = proc (p: pointer) {.nimcall, benign.}
+  TraceProc = proc (p, env: pointer) {.nimcall, benign, raises: [].}
+  DisposeProc = proc (p: pointer) {.nimcall, benign, raises: [].}
 
 template color(c): untyped = c.rc and colorMask
 template setColor(c, col) =

lib/system/gc.nim

@@ -62,6 +62,7 @@ comparisons).
 ]#
 
 {.push profiler:off.}
+{.push raises: [].}
 
 const
   CycleIncrease = 2 # is a multiplicative increase
@@ -914,4 +915,5 @@ when not defined(useNimRtl):
         result.add "[GC] stack bottom: " & gch.stack.bottom.repr
       result.add "[GC] max stack size: " & $gch.stat.maxStackSize & "\n"
 
+{.pop.} # raises: []
 {.pop.} # profiler: off, stackTrace: off

lib/system/gc_interface.nim

@@ -25,33 +25,33 @@ when hasAlloc and not defined(js) and not usesDestructors:
   proc GC_enable*() {.rtl, inl, benign, raises: [].}
     ## Enables the GC again.
 
-  proc GC_fullCollect*() {.rtl, benign.}
+  proc GC_fullCollect*() {.rtl, benign, raises: [].}
     ## Forces a full garbage collection pass.
     ## Ordinary code does not need to call this (and should not).
 
-  proc GC_enableMarkAndSweep*() {.rtl, benign.}
-  proc GC_disableMarkAndSweep*() {.rtl, benign.}
+  proc GC_enableMarkAndSweep*() {.rtl, benign, raises: [].}
+  proc GC_disableMarkAndSweep*() {.rtl, benign, raises: [].}
     ## The current implementation uses a reference counting garbage collector
     ## with a seldomly run mark and sweep phase to free cycles. The mark and
     ## sweep phase may take a long time and is not needed if the application
     ## does not create cycles. Thus the mark and sweep phase can be deactivated
     ## and activated separately from the rest of the GC.
 
-  proc GC_getStatistics*(): string {.rtl, benign.}
+  proc GC_getStatistics*(): string {.rtl, benign, raises: [].}
     ## Returns an informative string about the GC's activity. This may be useful
     ## for tweaking.
 
-  proc GC_ref*[T](x: ref T) {.magic: "GCref", benign.}
-  proc GC_ref*[T](x: seq[T]) {.magic: "GCref", benign.}
-  proc GC_ref*(x: string) {.magic: "GCref", benign.}
+  proc GC_ref*[T](x: ref T) {.magic: "GCref", benign, raises: [].}
+  proc GC_ref*[T](x: seq[T]) {.magic: "GCref", benign, raises: [].}
+  proc GC_ref*(x: string) {.magic: "GCref", benign, raises: [].}
     ## Marks the object `x` as referenced, so that it will not be freed until
     ## it is unmarked via `GC_unref`.
     ## If called n-times for the same object `x`,
     ## n calls to `GC_unref` are needed to unmark `x`.
 
-  proc GC_unref*[T](x: ref T) {.magic: "GCunref", benign.}
-  proc GC_unref*[T](x: seq[T]) {.magic: "GCunref", benign.}
-  proc GC_unref*(x: string) {.magic: "GCunref", benign.}
+  proc GC_unref*[T](x: ref T) {.magic: "GCunref", benign, raises: [].}
+  proc GC_unref*[T](x: seq[T]) {.magic: "GCunref", benign, raises: [].}
+  proc GC_unref*(x: string) {.magic: "GCunref", benign, raises: [].}
     ## See the documentation of `GC_ref <#GC_ref,string>`_.
 
   proc nimGC_setStackBottom*(theStackBottom: pointer) {.compilerRtl, noinline, benign, raises: [].}

lib/system/orc.nim

@@ -14,6 +14,8 @@
 # R.D. Lins / Information Processing Letters 109 (2008) 71–78
 #
 
+{.push raises: [].}
+
 include cellseqs_v2
 
 const
@@ -27,8 +29,8 @@ const
   logOrc = defined(nimArcIds)
 
 type
-  TraceProc = proc (p, env: pointer) {.nimcall, benign.}
-  DisposeProc = proc (p: pointer) {.nimcall, benign.}
+  TraceProc = proc (p, env: pointer) {.nimcall, benign, raises: [].}
+  DisposeProc = proc (p: pointer) {.nimcall, benign, raises: [].}
 
 template color(c): untyped = c.rc and colorMask
 template setColor(c, col) =
@@ -545,3 +547,5 @@ proc nimDecRefIsLastCyclicStatic(p: pointer; desc: PNimTypeV2): bool {.compilerR
       dec cell.rc, rcIncrement
     #if cell.color == colPurple:
     rememberCycle(result, cell, desc)
+
+{.pop.} # raises: []