Add support for .inc file extension in additional sketch code files

Describe the request

Add support for the use of code files with a .inc file extension in sketches:

https://arduino.github.io/arduino-cli/dev/sketch-specification/#additional-code-files

Describe the current behavior

If you compile a sketch that contains an #include directive for a file with a .inc extension that is present under the sketch folder, compilation fails with a "No such file or directory" error.

Arduino CLI version

1.4.0 Commit: b700097

the error can happen with arduino-cli Version: nightly-20260120 Commit: e394193 Date: 2026-01-20T01:37:42Z

Operating system

Linux

Operating system version

Linux howo-setup 6.17.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Mon, 24 Nov 2025 15:21:09 +0000 x86_64 GNU/Linux

Additional context

Forum discussion: https://forum.arduino.cc/t/help-arduino-cli-just-dont-compile-my-project/1424970

Additional requests

Issue checklist

I searched for previous requests in the issue tracker
I verified the feature was still missing when using the nightly build
My request contains all necessary details

Can you provide an example to reproduce the error?

yo

Makefile:

BOARD_FQBN 	:= digistump:avr:digispark-tiny
PORT       	:= /dev/hidraw0
BUILD_DIR  	:= build
SKETCH     	:= .

all: compile

compile:
	/tmp/arduino-cli compile \
	--fqbn $(BOARD_FQBN) \
	--output-dir $(BUILD_DIR) \
	$(SKETCH)

upload:
	/tmp/arduino-cli upload \
	--fqbn $(BOARD_FQBN) \
	--port $(PORT) \
	$(SKETCH)

clean:
	rm -rf $(BUILD_DIR)

rebuild: clean compile

.PHONY: all compile upload clean rebuild

Tree:

.
├── arduino.yaml
├── LICENSE
├── Makefile
├── README.md
├── SECURITY.md
├── SparkType.ino
└── src
    ├── include
    │   └── main.h
    ├── infra
    │   ├── HID
    │   │   ├── CONNECTION
    │   │   │   ├── main.cpp
    │   │   │   └── main.h
    │   │   └── LEDS
    │   │       ├── main.cpp
    │   │       └── main.h
    │   ├── OS
    │   │   ├── main.cpp
    │   │   └── main.h
    │   └── TTY
    │       ├── main.cpp
    │       └── main.h
    ├── lib
    │   ├── arduino-libraries
    │   │   └── DigisparkKeyboard
    │   │       └── src
    │   │           ├── ArduinoNotes.txt
    │   │           ├── asm
    │   │           │   ├── asmcommon.inc
    │   │           │   ├── usbdrvasm128.inc
    │   │           │   ├── usbdrvasm12.inc
    │   │           │   ├── usbdrvasm15.inc
    │   │           │   ├── usbdrvasm165.inc
    │   │           │   ├── usbdrvasm16.inc
    │   │           │   ├── usbdrvasm18-crc.inc
    │   │           │   └── usbdrvasm20.inc
    │   │           ├── Changelog.txt
    │   │           ├── CommercialLicense.txt
    │   │           ├── DigiKeyboard.cpp
    │   │           ├── DigiKeyboard.h
    │   │           ├── examples
    │   │           │   └── Keyboard
    │   │           │       └── Keyboard.ino
    │   │           ├── keylayouts.h
    │   │           ├── keywords.txt
    │   │           ├── License.txt
    │   │           ├── oddebug.c
    │   │           ├── oddebug.h
    │   │           ├── osccal.c
    │   │           ├── osccal.h
    │   │           ├── osctune.h
    │   │           ├── Readme.txt
    │   │           ├── scancode-ascii-table.h
    │   │           ├── usbboardconfig.h
    │   │           ├── usbconfig.h
    │   │           ├── usbconfig-prototype.h
    │   │           ├── usbdrvasm.asm
    │   │           ├── usbdrvasm.S
    │   │           ├── usbdrv.c
    │   │           ├── usbdrv.h
    │   │           ├── USB-ID-FAQ.txt
    │   │           ├── USBID-License.txt
    │   │           ├── USB-IDs-for-free.txt
    │   │           └── usbportability.h
    │   └── SparkKeyboard
    │       ├── ascii-map.txt
    │       ├── base-mods.txt
    │       ├── layouts
    │       │   └── pt-br
    │       │       ├── main.cpp
    │       │       └── main.h
    │       └── main.h
    ├── main.cpp
    └── shared
        └── utils
            └── blink-alert
                ├── main.cpp
                └── main.h

22 directories, 58 files

Error:

➜  SparkType git:(main) ✗ make
/tmp/arduino-cli compile \
--fqbn digistump:avr:digispark-tiny \
--output-dir build \
.
/home/yyax/Projects/SparkType/src/lib/arduino-libraries/DigisparkKeyboard/src/usbdrvasm.S:385:17: fatal error: asm/usbdrvasm16.inc: No such file or directory
 #       include "asm/usbdrvasm16.inc"
                 ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Used platform Version Path
digistump:avr 1.7.5   /home/yyax/.arduino15/packages/digistump/hardware/avr/1.7.5
Error during build: exit status 1
make: *** [Makefile:9: compile] Error 1
➜  SparkType git:(main) ✗

if i use absolute path the problem solves
but i can't as is a open source project

Thanks, can you run the compile with verbose enabled -v and copy the command that produces the include error?

/home/yyax/Projects/SparkType/src/lib/arduino-libraries/DigisparkKeyboard/src/usbdrvasm.S:385:17: fatal error: asm/usbdrvasm16.inc: No such file or directory
 #       include "asm/usbdrvasm16.inc"
                 ^~~~~~~~~~~~~~~~~~~~~

Thanks, can you run the compile with verbose enabled -v and copy the command that produces the include error?
/home/yyax/Projects/SparkType/src/lib/arduino-libraries/DigisparkKeyboard/src/usbdrvasm.S:385:17: fatal error: asm/usbdrvasm16.inc: No such file or directory
 #       include "asm/usbdrvasm16.inc"
                 ^~~~~~~~~~~~~~~~~~~~~

of course, but can you wait smt like 5 hours? i'm not in my lab so i can't run it now

can you wait smt like 5 hours? i'm not in my lab so i can't run it now

Yes, there is no rush. I'm going AFK too; we could continue tomorrow.

@Yyax13

Here is a minimal sketch to demonstrate the lack of .inc file support, without all the irrelevant complexity @Yyax13 crammed into their report:

3083.zip

3083/
├── 3083.ino
└── foo.inc

$ arduino-cli  version

arduino-cli  Version: 1.5.0 Commit: dd407d42d Date: 2026-05-21T20:11:07Z

$ arduino-cli  compile --fqbn arduino:zephyr:unoq

E:\3083\3083.ino:1:10: fatal error: foo.inc: No such file or directory
    1 | #include "foo.inc"
      |          ^~~~~~~~~
compilation terminated.

[...]

The contents of the sketch build folder:

sketch/
└── 3083.ino.cpp.merged

(note foo.inc was not copied to the build folder)

Note this is specific to sketch code files. #include directives for local files with any arbitrary extensions work in libraries. So those who use the "DigisparkKeyboard" library as intended would not experience any problem.

Navigation Menu

Repository navigation

Add support for `.inc` file extension in additional sketch code files #3083

Describe the request

Describe the current behavior

Arduino CLI version

Operating system

Operating system version

Additional context

Additional requests

Related

Issue checklist

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Add support for .inc file extension in additional sketch code files #3083

Description

Describe the request

Describe the current behavior

Arduino CLI version

Operating system

Operating system version

Additional context

Additional requests

Related

Issue checklist

Activity

cmaglie commented on Jan 21, 2026

Yyax13 commented on Jan 21, 2026

Yyax13 commented on Jan 21, 2026

cmaglie commented on Jan 21, 2026

Yyax13 commented on Jan 21, 2026

cmaglie commented on Jan 21, 2026

martin-eden commented on May 22, 2026

per1234 commented on May 22, 2026

per1234 commented on May 22, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Add support for `.inc` file extension in additional sketch code files #3083