.pde file extension not supported by compile when only folder specified

[per1234]

Bug Report

Current behavior

In the early days of Arduino, the .pde file extension of Processing sketches was used for Arduino sketches. Later, support for the dedicated .ino file extension was added, but support for .pde was retained. For this reason, some popular libraries still use the .pde extensions for their example sketches and the authors see no reason to bother changing that (reference).

I have a sketch:

Foo
|_Foo.pde

If I run the command:

arduino-cli compile --fqbn arduino:avr:uno Foo

It has the error:

Error during build: build failed: unable to find the main sketch file: open E:\Foo\Foo.ino: The system cannot find the file specified.

I can successfully run the command:

arduino-cli compile --fqbn arduino:avr:uno Foo/Foo.pde

but that will generate a default output filename that breaks the basic upload command (as reported in #355):

arduino-cli upload --fqbn arduino:avr:uno --port /dev/ttyACM0 Foo

Expected behavior

arduino-cli compile should work with sketches that use the .pde extension when only specifying the sketch folder as the path argument (as is recommended by the inline help).

Environment

• CLI version (output of arduino-cli version): nightly Commit: 3e0b555
• OS and platform: Windows 10 64 bit