From aa5d7c6d2fec21f32e5f36c8ec1597b91390717e Mon Sep 17 00:00:00 2001
From: kaizenman <kaizenman@users.noreply.github.com>
Date: Tue, 14 Apr 2026 23:55:03 +0200
Subject: [PATCH 1/2] Fix GP3 writeOldChord/readOldChord asymmetry

writeOldChord unconditionally wrote 6 fret ints after firstFret, but
readOldChord only reads them when firstFret != 0 (matching the Guitar Pro
byte layout). When a chord with firstFret == 0 was written and then read
back, 24 unread bytes remained in the stream, misaligning every following
read. The typical symptom was a later note's bend type byte being read as
-1, raising "ValueError: -1 is not a valid BendType".

Fix: only write the fret list when firstFret is non-zero.

Added tests/Chord Old Format.gp3 (derived from Chords.gp3 with the first
chord's newFormat set to False and firstFret set to 0). Without the fix
the new test fails with the exact error above; with the fix it passes.
---
 src/guitarpro/gp3.py       |   7 +++++--
 tests/Chord Old Format.gp3 | Bin 0 -> 1165 bytes
 tests/test_conversion.py   |   1 +
 3 files changed, 6 insertions(+), 2 deletions(-)
 create mode 100644 tests/Chord Old Format.gp3

diff --git a/src/guitarpro/gp3.py b/src/guitarpro/gp3.py
index d14d936..4d6fc56 100644
--- a/src/guitarpro/gp3.py
+++ b/src/guitarpro/gp3.py
@@ -1281,8 +1281,11 @@ def writeChord(self, chord):
     def writeOldChord(self, chord):
         self.writeIntByteSizeString(chord.name)
         self.writeI32(chord.firstFret)
-        for fret in clamp(chord.strings, 6, fillvalue=-1):
-            self.writeI32(fret)
+        # Fret list is only present when firstFret is non-zero; this
+        # matches readOldChord and the byte layout produced by Guitar Pro.
+        if chord.firstFret:
+            for fret in clamp(chord.strings, 6, fillvalue=-1):
+                self.writeI32(fret)
 
     def writeNewChord(self, chord):
         self.writeBool(chord.sharp)
diff --git a/tests/Chord Old Format.gp3 b/tests/Chord Old Format.gp3
new file mode 100644
index 0000000000000000000000000000000000000000..5a3d078d31105aca7e0639dfe3b65aed0f452962
GIT binary patch
literal 1165
zcmb1e^K|y`bPZB)5A_Uj3{nUP@>eJ`)-y0*00Tx4Ndy5_TmdE-7$ku-F9(D}YxaL2
zpqE{=@XM(C>61=y#T_leACzA}n3;uzfjy)sF*#eo5aLTbBpXo90f?=E*c^zBfLIrZ
zHGmidV1_aQ*%Dw828RDY8pLP%52hHMq2iDn3zcLB(jZ^fC@?Z8FfxKkCIv=jrvD%#
gu>*uj*yVwuFwHO;<PMlsI5j~e7=eHR-8mpB0MTJHjQ{`u

literal 0
HcmV?d00001

diff --git a/tests/test_conversion.py b/tests/test_conversion.py
index 28c1bc5..19b4649 100644
--- a/tests/test_conversion.py
+++ b/tests/test_conversion.py
@@ -10,6 +10,7 @@
 TESTS = [
     'Effects.gp3',
     'Chords.gp3',
+    'Chord Old Format.gp3',
     'Duration.gp3',
     'Harmonics.gp3',
     'Measure Header.gp3',

From bd84f2b8fd6be64749a654986698afcc7c8c9829 Mon Sep 17 00:00:00 2001
From: Sviatoslav Abakumov <dust.harvesting@gmail.com>
Date: Sat, 18 Apr 2026 17:22:20 +0400
Subject: [PATCH 2/2] fixup! Fix GP3 writeOldChord/readOldChord asymmetry

---
 src/guitarpro/gp3.py       |   2 --
 tests/Chord Old Format.gp3 | Bin 1165 -> 1052 bytes
 2 files changed, 2 deletions(-)

diff --git a/src/guitarpro/gp3.py b/src/guitarpro/gp3.py
index 4d6fc56..23e49f7 100644
--- a/src/guitarpro/gp3.py
+++ b/src/guitarpro/gp3.py
@@ -1281,8 +1281,6 @@ def writeChord(self, chord):
     def writeOldChord(self, chord):
         self.writeIntByteSizeString(chord.name)
         self.writeI32(chord.firstFret)
-        # Fret list is only present when firstFret is non-zero; this
-        # matches readOldChord and the byte layout produced by Guitar Pro.
         if chord.firstFret:
             for fret in clamp(chord.strings, 6, fillvalue=-1):
                 self.writeI32(fret)
diff --git a/tests/Chord Old Format.gp3 b/tests/Chord Old Format.gp3
index 5a3d078d31105aca7e0639dfe3b65aed0f452962..588f46b550895d7627251debe0d5260468eff7ca 100644
GIT binary patch
delta 99
scmeC>oWrr<AagVe0|NsS7%?z91KA8U3XBX2jErECNr91>ToDEa0RNW<@&Et;

delta 133
zcmbQk(aX8vAhQh<0|Nuoe+Cf6=nN#lfDuZAM45s3KM>R?Ffu4GGJ;7a1x9A3|BRCh
jnI)Kk+CcQ=24+qfm_8VdtRJd~orMtyCSPP021)_|a8(uJ