Tuple decoders set path

3 files changed, 80 insertions, 25 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a74ee6a..85afcef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,8 @@
 - The `dynamic.typed_tuple*` functions have been renamed to `dynamic.tuple*`.
 - The `dynamic.field` and `dynamic.element` functions now requires the type of
   the field to be specified.
+- The `dynamic.DecodeError` now has a `path` field.
+- The decoder functions of the `dynamic` module now return multiple errors.
 
 ## v0.18.1 - 2021-12-19
 
diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index 81a7a92..9a626dc 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -530,8 +530,12 @@ pub fn tuple2(
 ) -> Result(#(a, b), DecodeErrors) {
   try _ = assert_is_tuple(value, 2)
   let #(first, second) = unsafe_coerce(value)
-  try a = decode_first(first)
-  try b = decode_second(second)
+  try a =
+    decode_first(first)
+    |> map_errors(push_path(_, "0"))
+  try b =
+    decode_second(second)
+    |> map_errors(push_path(_, "1"))
   Ok(#(a, b))
 }
 
@@ -556,6 +560,19 @@ fn put_expected(error: DecodeError, expected: String) -> DecodeError {
   DecodeError(..error, expected: expected)
 }
 
+fn push_path(error: DecodeError, name: t) -> DecodeError {
+  let name = from(name)
+  let decoder = any(_, [string, fn(x) { result.map(int(x), int.to_string) }])
+  let name = case decoder(name) {
+    Ok(name) -> name
+    Error(_) ->
+      ["<", classify(name), ">"]
+      |> string_builder.from_strings
+      |> string_builder.to_string
+  }
+  DecodeError(..error, path: [name, ..error.path])
+}
+
 /// Checks to see if a `Dynamic` value is a 3-element tuple containing
 /// specifically typed elements.
 ///
@@ -581,9 +598,15 @@ pub fn tuple3(
 ) -> Result(#(a, b, c), DecodeErrors) {
   try _ = assert_is_tuple(value, 3)
   let #(first, second, third) = unsafe_coerce(value)
-  try a = decode_first(first)
-  try b = decode_second(second)
-  try c = decode_third(third)
+  try a =
+    decode_first(first)
+    |> map_errors(push_path(_, "0"))
+  try b =
+    decode_second(second)
+    |> map_errors(push_path(_, "1"))
+  try c =
+    decode_third(third)
+    |> map_errors(push_path(_, "2"))
   Ok(#(a, b, c))
 }
 
@@ -614,10 +637,18 @@ pub fn tuple4(
 ) -> Result(#(a, b, c, d), DecodeErrors) {
   try _ = assert_is_tuple(value, 4)
   let #(first, second, third, fourth) = unsafe_coerce(value)
-  try a = decode_first(first)
-  try b = decode_second(second)
-  try c = decode_third(third)
-  try d = decode_fourth(fourth)
+  try a =
+    decode_first(first)
+    |> map_errors(push_path(_, "0"))
+  try b =
+    decode_second(second)
+    |> map_errors(push_path(_, "1"))
+  try c =
+    decode_third(third)
+    |> map_errors(push_path(_, "2"))
+  try d =
+    decode_fourth(fourth)
+    |> map_errors(push_path(_, "3"))
   Ok(#(a, b, c, d))
 }
 
@@ -648,11 +679,21 @@ pub fn tuple5(
 ) -> Result(#(a, b, c, d, e), DecodeErrors) {
   try _ = assert_is_tuple(value, 5)
   let #(first, second, third, fourth, fifth) = unsafe_coerce(value)
-  try a = decode_first(first)
-  try b = decode_second(second)
-  try c = decode_third(third)
-  try d = decode_fourth(fourth)
-  try e = decode_fifth(fifth)
+  try a =
+    decode_first(first)
+    |> map_errors(push_path(_, "0"))
+  try b =
+    decode_second(second)
+    |> map_errors(push_path(_, "1"))
+  try c =
+    decode_third(third)
+    |> map_errors(push_path(_, "2"))
+  try d =
+    decode_fourth(fourth)
+    |> map_errors(push_path(_, "3"))
+  try e =
+    decode_fifth(fifth)
+    |> map_errors(push_path(_, "4"))
   Ok(#(a, b, c, d, e))
 }
 
@@ -684,12 +725,24 @@ pub fn tuple6(
 ) -> Result(#(a, b, c, d, e, f), DecodeErrors) {
   try _ = assert_is_tuple(value, 6)
   let #(first, second, third, fourth, fifth, sixth) = unsafe_coerce(value)
-  try a = decode_first(first)
-  try b = decode_second(second)
-  try c = decode_third(third)
-  try d = decode_fourth(fourth)
-  try e = decode_fifth(fifth)
-  try f = decode_sixth(sixth)
+  try a =
+    decode_first(first)
+    |> map_errors(push_path(_, "0"))
+  try b =
+    decode_second(second)
+    |> map_errors(push_path(_, "1"))
+  try c =
+    decode_third(third)
+    |> map_errors(push_path(_, "2"))
+  try d =
+    decode_fourth(fourth)
+    |> map_errors(push_path(_, "3"))
+  try e =
+    decode_fifth(fifth)
+    |> map_errors(push_path(_, "4"))
+  try f =
+    decode_sixth(sixth)
+    |> map_errors(push_path(_, "5"))
   Ok(#(a, b, c, d, e, f))
 }
 
diff --git a/test/gleam/dynamic_test.gleam b/test/gleam/dynamic_test.gleam
index f6622aa..7d490dc 100644
--- a/test/gleam/dynamic_test.gleam
+++ b/test/gleam/dynamic_test.gleam
@@ -380,7 +380,7 @@ pub fn tuple2_test() {
   |> dynamic.from
   |> dynamic.tuple2(dynamic.int, dynamic.int)
   |> should.equal(Error([
-    DecodeError(expected: "Int", found: "String", path: []),
+    DecodeError(expected: "Int", found: "String", path: ["1"]),
   ]))
 
   #(1, 2, 3)
@@ -417,7 +417,7 @@ pub fn tuple3_test() {
   |> dynamic.from
   |> dynamic.tuple3(dynamic.int, dynamic.int, dynamic.int)
   |> should.equal(Error([
-    DecodeError(expected: "Int", found: "String", path: []),
+    DecodeError(expected: "Int", found: "String", path: ["2"]),
   ]))
 
   #(1, 2)
@@ -454,7 +454,7 @@ pub fn tuple4_test() {
   |> dynamic.from
   |> dynamic.tuple4(dynamic.int, dynamic.int, dynamic.int, dynamic.int)
   |> should.equal(Error([
-    DecodeError(expected: "Int", found: "String", path: []),
+    DecodeError(expected: "Int", found: "String", path: ["3"]),
   ]))
 
   #(1, 2)
@@ -509,7 +509,7 @@ pub fn tuple5_test() {
     dynamic.int,
   )
   |> should.equal(Error([
-    DecodeError(expected: "Int", found: "String", path: []),
+    DecodeError(expected: "Int", found: "String", path: ["4"]),
   ]))
 
   #(1, 2)
@@ -579,7 +579,7 @@ pub fn tuple6_test() {
     dynamic.int,
   )
   |> should.equal(Error([
-    DecodeError(expected: "Int", found: "String", path: []),
+    DecodeError(expected: "Int", found: "String", path: ["5"]),
   ]))
 
   #(1, 2)