From c18e94e8d3044812ebfed8966dd4eabc5194c130 Mon Sep 17 00:00:00 2001
From: pnezis <pnezis@gmail.com>
Date: Mon, 9 Mar 2026 16:46:10 +0200
Subject: [PATCH] Fix `Float.parse/1` inconsistent error handling for
 non-scientific notation overflow

`Float.parse/1` was returning `:error` for overflow in scientific notation (e.g.,
"1.0e400") but raising `ArgumentError` for equivalent overflow in non-scientific
notation (e.g., a 310-digit number). This violated the documented behavior that
states `Float.parse/1` should return `:error` when the float exceeds the maximum
size.
---
 lib/elixir/lib/float.ex               | 17 +++--------------
 lib/elixir/test/elixir/float_test.exs |  5 +++++
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/lib/elixir/lib/float.ex b/lib/elixir/lib/float.ex
index 801fa649c8a..ac721dda52b 100644
--- a/lib/elixir/lib/float.ex
+++ b/lib/elixir/lib/float.ex
@@ -186,10 +186,9 @@ defmodule Float do
        when exp_marker in ~c"eE" and sign in ~c"-+" and digit in ?0..?9,
        do: parse_unsigned(rest, true, true, [digit, sign, ?e | add_dot(acc, dot?)])
 
-  # When floats are expressed in scientific notation, :erlang.binary_to_float/1 can raise an
-  # ArgumentError if the e exponent is too big. For example, "1.0e400". Because of this, we
-  # rescue the ArgumentError here and return an error.
-  defp parse_unsigned(rest, dot?, true = _e?, acc) do
+  # :erlang.binary_to_float/1 can raise an ArgumentError if the e exponent is too big. For example,
+  # "1.0e400". Because of this, we rescue the ArgumentError here and return an error.
+  defp parse_unsigned(rest, dot?, _, acc) do
     acc
     |> add_dot(dot?)
     |> :lists.reverse()
@@ -200,16 +199,6 @@ defmodule Float do
     float -> {float, rest}
   end
 
-  defp parse_unsigned(rest, dot?, false = _e?, acc) do
-    float =
-      acc
-      |> add_dot(dot?)
-      |> :lists.reverse()
-      |> :erlang.list_to_float()
-
-    {float, rest}
-  end
-
   defp add_dot(acc, true), do: acc
   defp add_dot(acc, false), do: [?0, ?. | acc]
 
diff --git a/lib/elixir/test/elixir/float_test.exs b/lib/elixir/test/elixir/float_test.exs
index fbc9230a490..945aca6ec67 100644
--- a/lib/elixir/test/elixir/float_test.exs
+++ b/lib/elixir/test/elixir/float_test.exs
@@ -57,6 +57,11 @@ defmodule FloatTest do
     assert Float.parse("1.7976931348623159e308") === :error
     assert Float.parse("1.7976931348623159e+308") === :error
     assert Float.parse("9e8363") === :error
+
+    # Non-scientific notation overflow
+    assert Float.parse(String.duplicate("9", 310) <> ".0") === :error
+    assert Float.parse("-" <> String.duplicate("9", 310) <> ".0") === :error
+    assert Float.parse(String.duplicate("9", 310) <> ".0foo") === :error
   end
 
   test "floor/1" do