From eabd5509d0c936759b82260d1e516425c020e880 Mon Sep 17 00:00:00 2001
From: Martin Vidner <martin@vidner.net>
Date: Fri, 11 Apr 2025 17:34:02 +0200
Subject: [PATCH] demonstrate bug: service provides array_of_hashes but
 misdeclares as a{sv}

This is an easy to make mistake because the spec unhelpfully
exposes the wire format and works with arrays of dictionary entries instead of
with hashes
---
 lib/dbus/data.rb                       |  3 +++
 lib/dbus/type.rb                       |  2 +-
 spec/mock-service/spaghetti-monster.rb |  6 ++++++
 spec/property_spec.rb                  | 14 ++++++++++++++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/dbus/data.rb b/lib/dbus/data.rb
index da8d5ec..8fa44c2 100644
--- a/lib/dbus/data.rb
+++ b/lib/dbus/data.rb
@@ -44,6 +44,9 @@ def make_typed(type, value)
       # not nil because DBus.type validates
 
       data_class.from_typed(value, type: type)
+    rescue StandardError => e
+      msg = "When making #{type.inspect} from an instance of #{value.class}: " + e.message
+      raise e.exception(msg)
     end
     module_function :make_typed
 
diff --git a/lib/dbus/type.rb b/lib/dbus/type.rb
index 4941605..ab1238f 100644
--- a/lib/dbus/type.rb
+++ b/lib/dbus/type.rb
@@ -363,7 +363,7 @@ def self.[](key_type, value_type)
     end
 
     # @example
-    #   t = Type::Hash[Type::INT16]
+    #   t = Type::Hash[Type::STRING, Type::VARIANT]
     Hash = HashFactory
 
     # Syntactic helper for constructing a struct Type.
diff --git a/spec/mock-service/spaghetti-monster.rb b/spec/mock-service/spaghetti-monster.rb
index f925374..50ee59f 100755
--- a/spec/mock-service/spaghetti-monster.rb
+++ b/spec/mock-service/spaghetti-monster.rb
@@ -46,6 +46,10 @@ def initialize(path)
       "two" => "dva",
       "three" => [3, 3, 3]
     }
+    # reproduce bug:
+    # type mismatch (user means to declare array_of_hashes as aa{sv})
+    # should produce informative error
+    @array_of_hashes = [@my_dict.dup]
     @my_variant = @my_array.dup
     # 201 is a RET instruction for ZX Spectrum which has turned 40 recently
     @my_byte = 201
@@ -140,6 +144,8 @@ def explosive
     dbus_attr_accessor :my_array, "aq"
     dbus_attr_accessor :my_dict, "a{sv}"
     dbus_attr_accessor :my_variant, "v"
+    # intentional bug to test reporting it: declaring an array of dict-entries instead
+    dbus_attr_reader :array_of_hashes, "a{sv}"
 
     dbus_attr_accessor :my_byte, "y"
 
diff --git a/spec/property_spec.rb b/spec/property_spec.rb
index 372dea4..60ded74 100755
--- a/spec/property_spec.rb
+++ b/spec/property_spec.rb
@@ -179,6 +179,20 @@
       val = @iface["MyArray"]
       expect(val).to eq([42, 43])
     end
+
+    it "a wrongly typed property provides a helpful message" do
+      # Now we get:
+      #   When getting 'org.ruby.SampleInterface.ArrayOfHashes':
+      #     When making ARRAY: [DICT_ENTRY: [STRING, VARIANT]] from an instance of Array:
+      #       When making DICT_ENTRY: [STRING, VARIANT] from an instance of Hash:
+      #         Specified type has 2 members but value has 3 members;
+      #           caused by 1 sender=:1.70...
+      # But we should really say
+      #    When making HASH: [STRING, VARIANT] from an instance of Array
+      # and document better this pitfall.
+      # Do we want to quote the entire data?
+      expect { @iface["ArrayOfHashes"] }.to raise_error(/DWIM/)
+    end
   end
 
   context "a dict-typed property" do