From: Benjamin Drung <benjamin.drung@canonical.com>
Date: Thu, 29 Sep 2022 11:05:41 +0200
Subject: Fix setting audacity_use_midi=off

When disabling MIDI support, cmake will fail:

```
$ cmake -B build -Daudacity_use_midi=off
[...]
CMake Error at cmake-proxies/CMakeLists.txt:314 (message):
  EXPERIMENTAL_MIDI_OUT requires USE_MIDI
```

Disable `EXPERIMENTAL_MIDI_OUT` in case MIDI support was explicitly
disabled.

Forwarded: https://github.com/audacity/audacity/pull/3717
Signed-off-by: Benjamin Drung <benjamin.drung@canonical.com>
---
 src/Experimental.cmake | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/Experimental.cmake b/src/Experimental.cmake
index b82b38e..28fad38 100644
--- a/src/Experimental.cmake
+++ b/src/Experimental.cmake
@@ -69,18 +69,6 @@ set( EXPERIMENTAL_OPTIONS_LIST
    # Paul Licameli (PRL) 29 Nov 2014
    #IMPROVED_SEEKING
 
-   #MIDI_IN
-
-   # JKC, 17 Aug 2017
-   # Enables the MIDI note stretching feature, which currently
-   # a) Is broken on Linux (Bug 1646)
-   # b) Crashes with Sync-Lock (Bug 1719)
-   # c) Needs UI design review.
-   #MIDI_STRETCHING
-
-   # USE_MIDI must be defined in order for SCOREALIGN to work
-   #SCOREALIGN
-
    #Automatically tries to find an acceptable input volume
    #AUTOMATED_INPUT_LEVEL_ADJUSTMENT
 
@@ -108,6 +96,22 @@ set( EXPERIMENTAL_OPTIONS_LIST
    # EASY_CHANGE_KEY_BINDINGS
 )
 
+if( NOT audacity_use_midi STREQUAL "off" )
+   list( APPEND EXPERIMENTAL_OPTIONS_LIST
+   #MIDI_IN
+
+   # JKC, 17 Aug 2017
+   # Enables the MIDI note stretching feature, which currently
+   # a) Is broken on Linux (Bug 1646)
+   # b) Crashes with Sync-Lock (Bug 1719)
+   # c) Needs UI design review.
+   #MIDI_STRETCHING
+
+   # USE_MIDI must be defined in order for SCOREALIGN to work
+   #SCOREALIGN
+  )
+endif()
+
 # Now define the flags
 list( TRANSFORM EXPERIMENTAL_OPTIONS_LIST PREPEND "EXPERIMENTAL_"  )
 add_compile_definitions( ${EXPERIMENTAL_OPTIONS_LIST} )