rpc: Quote user supplied descriptor in error msg

Author: MarcoFalke

src/script/descriptor.cpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2018-2021 The Bitcoin Core developers
+// Copyright (c) 2018-2022 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -1222,7 +1222,7 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
         error = "A function is needed within P2WSH";
         return nullptr;
     }
-    error = strprintf("%s is not a valid descriptor function", std::string(expr.begin(), expr.end()));
+    error = strprintf("'%s' is not a valid descriptor function", std::string(expr.begin(), expr.end()));
     return nullptr;
 }
 

test/functional/rpc_getdescriptorinfo.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright (c) 2019-2020 The Bitcoin Core developers
+# Copyright (c) 2019-2022 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test getdescriptorinfo RPC.
@@ -30,7 +30,7 @@ def test_desc(self, desc, isrange, issolvable, hasprivatekeys):
     def run_test(self):
         assert_raises_rpc_error(-1, 'getdescriptorinfo', self.nodes[0].getdescriptorinfo)
         assert_raises_rpc_error(-3, 'Expected type string', self.nodes[0].getdescriptorinfo, 1)
-        assert_raises_rpc_error(-5, 'is not a valid descriptor function', self.nodes[0].getdescriptorinfo, '')
+        assert_raises_rpc_error(-5, "'' is not a valid descriptor function", self.nodes[0].getdescriptorinfo, "")
 
         # P2PK output with the specified public key.
         self.test_desc('pk(0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798)', isrange=False, issolvable=True, hasprivatekeys=False)