Merge pull request #19 from JuliaObjects/setproperr

Improve setproperties error message

Author: jw3126

src/ConstructionBase.jl

@@ -39,32 +39,37 @@ struct NamedTupleConstructor{names} end
     end
 end
 
-function assert_hasfields(T, fnames)
-    for fname in fnames
-        if !(fname in fieldnames(T))
-            msg = "$T has no field $fname"
-            throw(ArgumentError(msg))
-        end
-    end
-end
-
 function setproperties(obj; kw...)
     setproperties(obj, (;kw...))
 end
 
 @generated function setproperties(obj, patch::NamedTuple)
-    assert_hasfields(obj, fieldnames(patch))
-    args = map(fieldnames(obj)) do fn
-        if fn in fieldnames(patch)
-            :(patch.$fn)
-        else
-            :(obj.$fn)
+    if issubset(fieldnames(patch), fieldnames(obj))
+        args = map(fieldnames(obj)) do fn
+            if fn in fieldnames(patch)
+                :(patch.$fn)
+            else
+                :(obj.$fn)
+            end
         end
+        return Expr(:block,
+            Expr(:meta, :inline),
+            Expr(:call,:(constructorof($obj)), args...)
+        )
+    else
+        :(setproperties_unknown_field_error(obj, patch))
     end
-    Expr(:block,
-        Expr(:meta, :inline),
-        Expr(:call,:(constructorof($obj)), args...)
-    )
+end
+
+function setproperties_unknown_field_error(obj, patch)
+    O = typeof(obj)
+    P = typeof(patch)
+    msg = """
+    Failed to assign properties $(fieldnames(P)) to object with fields $(fieldnames(O)).
+    You may want to overload
+    ConstructionBase.setproperties(obj::$O, patch::NamedTuple)
+    """
+    throw(ArgumentError(msg))
 end
 
 

test/runtests.jl

@@ -24,8 +24,18 @@ end
     @test setproperties(o, (a=2, b=3.0)) === AB(2,3.0)
     @test setproperties(o, a=2, b=3.0) === AB(2,3.0)
 
-    @test_throws ArgumentError setproperties(o, (a=2, c=3.0))
-    @test_throws ArgumentError setproperties(o, a=2, c=3.0)
+    res = @test_throws ArgumentError setproperties(o, (a=2, this_field_does_not_exist=3.0))
+    msg = sprint(showerror, res.value)
+    @test occursin("this_field_does_not_exist", msg)
+    @test occursin("overload", msg)
+    @test occursin("ConstructionBase.setproperties", msg)
+
+    res = @test_throws ArgumentError setproperties(o, a=2, this_field_does_not_exist=3.0)
+    msg = sprint(showerror, res.value)
+    @test occursin("this_field_does_not_exist", msg)
+    @test occursin("overload", msg)
+    @test occursin("ConstructionBase.setproperties", msg)
+
     @test setproperties(Empty(), NamedTuple()) === Empty()
     @test setproperties(Empty()) === Empty()