Prototype not generated for function with inline attribute

[per1234]

Describe the problem

In order to make it easier for beginners to get started with writing Arduino sketches, and for the convenience of all users, Arduino CLI automatically generates and adds prototypes for functions defined in a .ino file of a sketch.

Attributes can be used to specify properties of a function. The attribute declaration may be placed at a variety of locations relative to a function definition.

🐛 A prototype is not generated for the function if the attribute declaration is placed between the type and name in the function definition.

To reproduce

Setup environment

$ arduino-cli version

arduino-cli  Version: git-snapshot Commit: c5812eea6 Date: 2024-09-02T17:16:38Z

$ mkdir -P "/tmp/FooSketch"

$ printf '
void loop() {}
void setup() {
  foo();
}
void __attribute__(()) foo() {}
' > "/tmp/FooSketch/FooSketch.ino"

Demo

$ arduino-cli compile --fqbn arduino:avr:uno "/tmp/FooSketch"

C:\Users\per\AppData\Local\Temp\FooSketch\FooSketch.ino: In function 'void setup()':
C:\Users\per\AppData\Local\Temp\FooSketch\FooSketch.ino:3:3: error: 'foo' was not declared in this scope
   foo();
   ^~~

🐛 The compilation failed unexpectedly.

By looking at the C++ code generated by the Arduino sketch preprocessor, we can see the cause of the error:

$ arduino-cli compile --fqbn arduino:avr:uno --preprocess "/tmp/FooSketch"

#include <Arduino.h>
#line 1 "C:\\Users\\per\\AppData\\Local\\Temp\\FooSketch\\FooSketch.ino"
#line 1 "C:\\Users\\per\\AppData\\Local\\Temp\\FooSketch\\FooSketch.ino"
void loop();
#line 2 "C:\\Users\\per\\AppData\\Local\\Temp\\FooSketch\\FooSketch.ino"
void setup();
#line 1 "C:\\Users\\per\\AppData\\Local\\Temp\\FooSketch\\FooSketch.ino"
void loop() {}
void setup() {
  foo();
}
void __attribute__(()) foo() {}

🐛 The compilation failure was caused by Arduino CLI not creating a prototype for the foo function.

Expected behavior

Prototypes are generated for functions with attribute declarations between the type and name.

Arduino CLI version

c5812ee

Operating system

• Windows

Operating system version

• Windows 11

Additional context

Originally reported by @JLBCS at https://forum.arduino.cc/t/iram-attr-questions/1297715

In the real world sketch shared there, IRAM_ATTR was used. This is a macro for an __attribute__ declaration, provided by Espressif's esp-idf framework.

Additional reports

• https://forum.arduino.cc/t/attachinterrupt-blows-up-in-my-simple-8266-sketch/1314984/3

Related

• #line directives inserted into raw string literal by sketch preprocessor #1191
• ) in comment breaks function prototype generation #1253
• Generated function prototype injected before declaration of custom parameter type #1269
• Generated prototype incorrectly prefixed with extern "C" when comment contains // #1591
• Generated prototype incorrectly prefixed with extern "C" when using extern "C" { ... } to mix C functions in an .ino file. #1618
• Backslash incorrectly inserted into generated prototype for multiline template function  #1785
• An other preprocessing bug (probably). #1822
• Prototype incorrectly generated for struct member function under certain conditions #2161
• Enum defined after a function template cannot be compiled #2525
• https://forum.arduino.cc/t/is-the-location-of-a-global-function-important/996378/18
• https://forum.arduino.cc/t/ide-mistakes-javascript-function-for-type/953022
• https://forum.arduino.cc/t/c-super-quotes-compiler-bug/990071
• https://forum.arduino.cc/t/over-length-line-in-editor-forces-forward-declaration/955571
• https://forum.arduino.cc/t/solved-multiple-ide-tabs-issue/988086
• https://forum.arduino.cc/t/declaration-of-functions/687199/11
• https://forum.arduino.cc/t/tab-local-structs/689088
• https://forum.arduino.cc/t/include-in-multiple-sketches/1133645/11
• https://forum.arduino.cc/t/compiler-flaw-probably-deliberate-infuriating/1146637
• https://forum.arduino.cc/t/does-the-ardiuno-compiler-fully-support-templates/1274584

Workaround

Manually add a function prototype to the sketch:

void __attribute__(()) foo();
void loop() {}
void setup() {
  foo();
}
void foo() {}

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details