"mbed compile" fails with "list index out of range"

[infinnovation-dev]

Description

• Type: Bug
• Related issue: #abc
• Priority: Minor

---

Bug

Target
K64F

Toolchain:
GCC_ARM

Toolchain version:
4_9-2015q3

mbed-cli version:
0.9.10

meed-os sha:
e2617cc

Expected behavior
Failed compilation should not propagate to next compilation attempt

Actual behavior
In some circumstances, a failed compilation results in the next "mbed compile" reporting

...
Scan: mbed
Scan: env
[ERROR] list index out of range
[mbed] ERROR: "python" returned error code 1.

Steps to reproduce
Ah, you've got me there! I haven't been able to determine the exact circumstances. What I have found is that somehow a .d file may be left empty after a failed compilation. In one example, the error was a missing include file referenced by main.cpp, but the file BUILD/K64F/GCC_ARM/mbed-os/events/equeue/equeue_mbed.d was left empty.

When an empty .d file is present, GCC.parse_dependencies in tools/toolschains/gcc,py falls over when trying to access the first line of the file.

[0xc0170]

cc @theotherjimmy

[theotherjimmy]

So your steps to reproduce would be to take a clean repo and create an empty .d file.

[theotherjimmy]

Reproduced artificially by:

$ echo -n > BUILD/K64F/gcc_arm/main.d

[theotherjimmy]

@infinnovation could you review #3229 ?