Don't raise on overflowing floats in Float.parse/1 (#12099)

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 and return an error.

Author: whatyouhide

lib/elixir/lib/float.ex

@@ -119,7 +119,8 @@ defmodule Float do
   returned.
 
   If the size of float exceeds the maximum size of `1.7976931348623157e+308`,
-  the `ArgumentError` exception is raised.
+  `:error` is returned even though the textual representation itself might be
+  well formed.
 
   If you want to convert a string-formatted float directly to a float,
   `String.to_float/1` can be used instead.
@@ -135,6 +136,8 @@ defmodule Float do
 
       iex> Float.parse("pi")
       :error
+      iex> Float.parse("1.7976931348623159e+308")
+      :error
 
   """
   @spec parse(binary) :: {float, binary} | :error
@@ -172,7 +175,18 @@ defmodule Float do
        when exp_marker in 'eE' and sign in '-+' and digit in ?0..?9,
        do: parse_unsigned(rest, true, true, <<add_dot(acc, dot?)::binary, ?e, sign, digit>>)
 
-  defp parse_unsigned(rest, dot?, _e?, acc),
+  # 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(add_dot(acc, dot?))
+  rescue
+    ArgumentError -> :error
+  else
+    float -> {float, rest}
+  end
+
+  defp parse_unsigned(rest, dot?, false = _e?, acc),
     do: {:erlang.binary_to_float(add_dot(acc, dot?)), rest}
 
   defp add_dot(acc, true), do: acc

lib/elixir/test/elixir/float_test.exs

@@ -24,6 +24,7 @@ defmodule FloatTest do
     assert Float.parse("-12.32453e-10") === {-1.232453e-9, ""}
     assert Float.parse("0.32453e-10") === {3.2453e-11, ""}
     assert Float.parse("1.32453e-10") === {1.32453e-10, ""}
+    assert Float.parse("1.7976931348623159e-99999foo") === {0.0, "foo"}
     assert Float.parse("1.32.45") === {1.32, ".45"}
     assert Float.parse("1.o") === {1.0, ".o"}
     assert Float.parse("+12.3E+4") === {1.23e5, ""}
@@ -35,10 +36,12 @@ defmodule FloatTest do
     assert Float.parse("++1.2") === :error
     assert Float.parse("pi") === :error
     assert Float.parse("1.7976931348623157e308") === {1.7976931348623157e308, ""}
-
-    assert_raise ArgumentError, fn ->
-      Float.parse("1.7976931348623159e308")
-    end
+    assert Float.parse("1.7976931348623157e308foo") === {1.7976931348623157e308, "foo"}
+    assert Float.parse("1.7976931348623157e+308foo") === {1.7976931348623157e308, "foo"}
+    assert Float.parse("1.7976931348623157e-308foo") === {1.7976931348623155e-308, "foo"}
+    assert Float.parse("1.7976931348623159e308") === :error
+    assert Float.parse("1.7976931348623159e+308") === :error
+    assert Float.parse("9e8363") === :error
   end
 
   test "floor/1" do