backport: merge bitcoin#18952,18817

src/qt/bitcoin.cpp

@@ -206,6 +206,7 @@ BitcoinApplication::BitcoinApplication(interfaces::Node& node):
     pollShutdownTimer(nullptr),
     returnValue(0)
 {
+    // Qt runs setlocale(LC_ALL, "") on initialization.
     setQuitOnLastWindowClosed(false);
 }
 

test/functional/test_framework/test_framework.py

@@ -238,8 +238,18 @@ def setup(self):
 
         config = self.config
 
-        self.options.bitcoind = os.getenv("BITCOIND", default=config["environment"]["BUILDDIR"] + '/src/dashd' + config["environment"]["EXEEXT"])
-        self.options.bitcoincli = os.getenv("BITCOINCLI", default=config["environment"]["BUILDDIR"] + '/src/dash-cli' + config["environment"]["EXEEXT"])
+        fname_bitcoind = os.path.join(
+            config["environment"]["BUILDDIR"],
+            "src",
+            "dashd" + config["environment"]["EXEEXT"]
+        )
+        fname_bitcoincli = os.path.join(
+            config["environment"]["BUILDDIR"],
+            "src",
+            "dash-cli" + config["environment"]["EXEEXT"]
+        )
+        self.options.bitcoind = os.getenv("BITCOIND", default=fname_bitcoind)
+        self.options.bitcoincli = os.getenv("BITCOINCLI", default=fname_bitcoincli)
 
         self.extra_args_from_options = self.options.dashd_extra_args
 

test/lint/lint-locale-dependence.sh

@@ -8,6 +8,39 @@ export LC_ALL=C
 # TODO: Reduce KNOWN_VIOLATIONS by replacing uses of locale dependent stoul/strtol with locale
 #       independent ToIntegral<T>(...).
 # TODO: Reduce KNOWN_VIOLATIONS by replacing uses of locale dependent snprintf with strprintf.
+
+# Be aware that bitcoind and bitcoin-qt differ in terms of localization: Qt
+# opts in to POSIX localization by running setlocale(LC_ALL, "") on startup,
+# whereas no such call is made in bitcoind.
+#
+# Qt runs setlocale(LC_ALL, "") on initialization. This installs the locale
+# specified by the user's LC_ALL (or LC_*) environment variable as the new
+# C locale.
+#
+# In contrast, bitcoind does not opt in to localization -- no call to
+# setlocale(LC_ALL, "") is made and the environment variables LC_* are
+# thus ignored.
+#
+# This results in situations where bitcoind is guaranteed to be running
+# with the classic locale ("C") whereas the locale of bitcoin-qt will vary
+# depending on the user's environment variables.
+#
+# An example: Assuming the environment variable LC_ALL=de_DE then the
+# call std::to_string(1.23) will return "1.230000" in bitcoind but
+# "1,230000" in bitcoin-qt.
+#
+# From the Qt documentation:
+# "On Unix/Linux Qt is configured to use the system locale settings by default.
+#  This can cause a conflict when using POSIX functions, for instance, when
+#  converting between data types such as floats and strings, since the notation
+#  may differ between locales. To get around this problem, call the POSIX function
+#  setlocale(LC_NUMERIC,"C") right after initializing QApplication, QGuiApplication
+#  or QCoreApplication to reset the locale that is used for number formatting to
+#  "C"-locale."
+#
+# See https://doc.qt.io/qt-5/qcoreapplication.html#locale-settings and
+# https://stackoverflow.com/a/34878283 for more details.
+
 KNOWN_VIOLATIONS=(
     "src/bitcoin-tx.cpp.*stoul"
     "src/dbwrapper.cpp.*stoul"