Add errorhint for nonexisting fields and properties (#55165)

I played a bit with error hints and crafted this: ```julia julia> (1+2im).real ERROR: FieldError: type Complex has no field real, available fields: `re`, `im` julia> nothing.xy ERROR: FieldError: type Nothing has no field xy; Nothing has no fields at all. julia> svd(rand(2,2)).VV ERROR: FieldError: type SVD has no field VV, available fields: `U`, `S`, `Vt` Available properties: `V` ``` --------- Co-authored-by: Lilith Orion Hafner <[email protected]>
JuliaLang · Sep 20, 2024 · 220742d · 220742d · Zentrik · Sep 26, 2024
1 parent 7f7a472
commit 220742d
Show file tree

Hide file tree

Showing 4 changed files with 39 additions and 10 deletions.
diff --git a/base/docs/basedocs.jl b/base/docs/basedocs.jl
@@ -1694,7 +1694,7 @@ julia> ab = AB(1, 3)
 AB(1.0f0, 3.0)
 
 julia> ab.c # field `c` doesn't exist
-ERROR: FieldError: type AB has no field c
+ERROR: FieldError: type AB has no field `c`, available fields: `a`, `b`
 Stacktrace:
 [...]
 ```

diff --git a/base/errorshow.jl b/base/errorshow.jl
@@ -378,7 +378,7 @@ end
 
 function showerror(io::IO, exc::FieldError)
     @nospecialize
-    print(io, "FieldError: type $(exc.type |> nameof) has no field $(exc.field)")
+    print(io, "FieldError: type $(exc.type |> nameof) has no field `$(exc.field)`")
     Base.Experimental.show_error_hints(io, exc)
 end
 
@@ -1102,7 +1102,7 @@ end
 Experimental.register_error_hint(methods_on_iterable, MethodError)
 
 # Display a hint in case the user tries to access non-member fields of container type datastructures
-function fielderror_hint_handler(io, exc)
+function fielderror_dict_hint_handler(io, exc)
     @nospecialize
     field = exc.field
     type = exc.type
@@ -1113,7 +1113,32 @@ function fielderror_hint_handler(io, exc)
     end
 end
 
-Experimental.register_error_hint(fielderror_hint_handler, FieldError)
+Experimental.register_error_hint(fielderror_dict_hint_handler, FieldError)
+
+function fielderror_listfields_hint_handler(io, exc)
+    fields = fieldnames(exc.type)
+    if isempty(fields)
+        print(io, "; $(nameof(exc.type)) has no fields at all.")
+    else
+        print(io, ", available fields: $(join(map(k -> "`$k`", fields), ", "))")
+    end
+    props = _propertynames_bytype(exc.type)
+    isnothing(props) && return
+    props = setdiff(props, fields)
+    isempty(props) && return
+    print(io, "\nAvailable properties: $(join(map(k -> "`$k`", props), ", "))")
+end
+
+function _propertynames_bytype(T::Type)
+    which(propertynames, (T,)) === which(propertynames, (Any,)) && return nothing
+    inferred_names = promote_op(Val∘propertynames, T)
+    inferred_names isa DataType && inferred_names <: Val || return nothing
+    inferred_names = inferred_names.parameters[1]
+    inferred_names isa NTuple{<:Any, Symbol} || return nothing
+    return Symbol[inferred_names[i] for i in 1:length(inferred_names)]
+end
+
+Experimental.register_error_hint(fielderror_listfields_hint_handler, FieldError)
 
 # ExceptionStack implementation
 size(s::ExceptionStack) = size(s.stack)

diff --git a/base/reflection.jl b/base/reflection.jl
@@ -1017,7 +1017,7 @@ julia> struct Foo
        end
 
 julia> Base.fieldindex(Foo, :z)
-ERROR: FieldError: type Foo has no field z
+ERROR: FieldError: type Foo has no field `z`, available fields: `x`, `y`
 Stacktrace:
 [...]
 

diff --git a/test/errorshow.jl b/test/errorshow.jl
@@ -10,7 +10,8 @@ Base.Experimental.register_error_hint(Base.noncallable_number_hint_handler, Meth
 Base.Experimental.register_error_hint(Base.string_concatenation_hint_handler, MethodError)
 Base.Experimental.register_error_hint(Base.methods_on_iterable, MethodError)
 Base.Experimental.register_error_hint(Base.nonsetable_type_hint_handler, MethodError)
-Base.Experimental.register_error_hint(Base.fielderror_hint_handler, FieldError)
+Base.Experimental.register_error_hint(Base.fielderror_listfields_hint_handler, FieldError)
+Base.Experimental.register_error_hint(Base.fielderror_dict_hint_handler, FieldError)
 
 @testset "SystemError" begin
     err = try; systemerror("reason", Cint(0)); false; catch ex; ex; end::SystemError
@@ -808,12 +809,13 @@ end
 @test_throws ArgumentError("invalid index: \"foo\" of type String") [1]["foo"]
 @test_throws ArgumentError("invalid index: nothing of type Nothing") [1][nothing]
 
-# issue #53618
-@testset "FieldErrorHint" begin
+# issue #53618, pr #55165
+@testset "FieldErrorHints" begin
     struct FieldFoo
         a::Float32
         b::Int
     end
+    Base.propertynames(foo::FieldFoo) = (:a, :x, :y)
 
     s = FieldFoo(1, 2)
 
@@ -823,7 +825,9 @@ end
 
     # Check error message first
     errorMsg = sprint(Base.showerror, ex)
-    @test occursin("FieldError: type FieldFoo has no field c", errorMsg)
+    @test occursin("FieldError: type FieldFoo has no field `c`", errorMsg)
+    @test occursin("available fields: `a`, `b`", errorMsg)
+    @test occursin("Available properties: `x`, `y`", errorMsg)
 
     d = Dict(s => 1)
 
@@ -840,7 +844,7 @@ end
     ex = test.value::FieldError
 
     errorMsg = sprint(Base.showerror, ex)
-    @test occursin("FieldError: type Dict has no field c", errorMsg)
+    @test occursin("FieldError: type Dict has no field `c`", errorMsg)
     # Check hint message
     hintExpected = "Did you mean to access dict values using key: `:c` ? Consider using indexing syntax dict[:c]\n"
     @test occursin(hintExpected, errorMsg)