From 3694ae88f6fd8d08fd150fe39823666ada503873 Mon Sep 17 00:00:00 2001
From: Thomas Pelletier <pelletier.thomas@gmail.com>
Date: Thu, 28 Oct 2021 20:41:10 -0400
Subject: [PATCH] decode: error on _ before exponent in floats (#647)

Fixes #646
---
 decode.go           |  3 +++
 unmarshaler_test.go | 22 ++++++++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/decode.go b/decode.go
index cd21bee..25e69c4 100644
--- a/decode.go
+++ b/decode.go
@@ -405,6 +405,9 @@ func checkAndRemoveUnderscoresFloats(b []byte) ([]byte, error) {
 			if !before {
 				return nil, newDecodeError(b[i-1:i+1], "number must have at least one digit between underscores")
 			}
+			if i < len(b)-1 && (b[i+1] == 'e' || b[i+1] == 'E') {
+				return nil, newDecodeError(b[i+1:i+2], "cannot have underscore before exponent")
+			}
 			before = false
 		case 'e', 'E':
 			if i < len(b)-1 && b[i+1] == '_' {
diff --git a/unmarshaler_test.go b/unmarshaler_test.go
index 6ccd2d0..6259b3a 100644
--- a/unmarshaler_test.go
+++ b/unmarshaler_test.go
@@ -204,6 +204,16 @@ func TestUnmarshal_Floats(t *testing.T) {
 				assert.True(t, math.IsNaN(v))
 			},
 		},
+		{
+			desc:  "underscore after integer part",
+			input: `1_e2`,
+			err:   true,
+		},
+		{
+			desc:  "underscore after integer part",
+			input: `1.0_e2`,
+			err:   true,
+		},
 	}
 
 	type doc struct {
@@ -215,11 +225,15 @@ func TestUnmarshal_Floats(t *testing.T) {
 		t.Run(e.desc, func(t *testing.T) {
 			doc := doc{}
 			err := toml.Unmarshal([]byte(`A = `+e.input), &doc)
-			require.NoError(t, err)
-			if e.testFn != nil {
-				e.testFn(t, doc.A)
+			if e.err {
+				require.Error(t, err)
 			} else {
-				assert.Equal(t, e.expected, doc.A)
+				require.NoError(t, err)
+				if e.testFn != nil {
+					e.testFn(t, doc.A)
+				} else {
+					assert.Equal(t, e.expected, doc.A)
+				}
 			}
 		})
 	}