fixes #25263; provides a new switch mangle:nim/cpp for debug name mangling (#25264)

fixes #25263

- [x] documentation and changelogs

compiler/ccgtypes.nim

@@ -75,7 +75,7 @@ proc mangleProc(m: BModule; s: PSym; makeUnique: bool): string =
 proc fillBackendName(m: BModule; s: PSym) =
   if s.loc.snippet == "":
     var result: Rope
-    if not m.compileToCpp and s.kind in routineKinds and optCDebug in m.g.config.globalOptions and
+    if s.kind in routineKinds and {optCDebug, optItaniumMangle} * m.g.config.globalOptions == {optCDebug, optItaniumMangle} and
       m.g.config.symbolFiles == disabledSf:
       result = mangleProc(m, s, false).rope
     else:

compiler/commands.nim

@@ -364,6 +364,7 @@ proc testCompileOption*(conf: ConfigRef; switch: string, info: TLineInfo): bool
     result = false
   of "panics": result = contains(conf.globalOptions, optPanics)
   of "jsbigint64": result = contains(conf.globalOptions, optJsBigInt64)
+  of "mangle": result = contains(conf.globalOptions, optItaniumMangle)
   else:
     result = false
     invalidCmdLineOption(conf, passCmd1, switch, info)
@@ -762,6 +763,14 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
       conf.globalOptions.excl optCDebug
     else:
       localError(conf, info, "expected native|gdb|on|off but found " & arg)
+  of "mangle":
+    case arg.normalize
+    of "nim":
+      conf.globalOptions.excl optItaniumMangle
+    of "cpp":
+      conf.globalOptions.incl optItaniumMangle
+    else:
+      localError(conf, info, "expected nim|cpp but found " & arg)
   of "g": # alias for --debugger:native
     conf.globalOptions.incl optCDebug
     conf.options.incl optLineDir

compiler/options.nim

@@ -110,6 +110,7 @@ type                          # please make sure we have under 32 options
     optEnableDeepCopy         # ORC specific: enable 'deepcopy' for all types.
     optShowNonExportedFields  # for documentation: show fields that are not exported
     optJsBigInt64             # use bigints for 64-bit integers in JS
+    optItaniumMangle          # mangling follows the Itanium spec
 
   TGlobalOptions* = set[TGlobalOption]