logging: Ensure -debug=0/none behaves consistently with -nodebug

Previously, -nodebug cleared all prior -debug configurations in the
command line while allowing subsequent debug options to be applied.
However, -debug=0 and -debug=none completely disabled debugging,
even for categories specified afterward.

This commit ensures consistency by making -debug=0 and -debug=none
behave like -nodebug: they now clear previously set debug configurations
but do not disable debugging for categories specified later.

Co-Authored-By: Ryan Ofsky <ryan@ofsky.org>

Author: danielabrozzoni

doc/release-notes-31767.md

@@ -0,0 +1,3 @@
+Logging
+---
+Passing -debug=0 or -debug=none now behaves like -nodebug: previously set debug categories will be cleared, but subsequent -debug options will still be applied.

src/init/common.cpp

@@ -80,15 +80,17 @@ util::Result<void> SetLoggingLevel(const ArgsManager& args)
 util::Result<void> SetLoggingCategories(const ArgsManager& args)
 {
     if (args.IsArgSet("-debug")) {
-        // Special-case: if -debug=0/-nodebug is set, turn off debugging messages
         const std::vector<std::string> categories = args.GetArgs("-debug");
 
-        if (std::none_of(categories.begin(), categories.end(),
-            [](std::string cat){return cat == "0" || cat == "none";})) {
-            for (const auto& cat : categories) {
-                if (!LogInstance().EnableCategory(cat)) {
-                    return util::Error{strprintf(_("Unsupported logging category %s=%s."), "-debug", cat)};
-                }
+        // Special-case: Disregard any debugging categories appearing before -debug=0/none
+        const auto last_negated = std::find_if(categories.rbegin(), categories.rend(),
+                                               [](const std::string& cat) { return cat == "0" || cat == "none"; });
+
+        const auto categories_to_process = (last_negated == categories.rend()) ? categories : std::ranges::subrange(last_negated.base(), categories.end());
+
+        for (const auto& cat : categories_to_process) {
+            if (!LogInstance().EnableCategory(cat)) {
+                return util::Error{strprintf(_("Unsupported logging category %s=%s."), "-debug", cat)};
             }
         }
     }