mbed-cli ignores config when mbed_app.json invalid

[bremoran]

mbed-cli builds anyway when mbed_app.json is invalid, which leads to unexpected debugging errors.

[screamerbg]

cc @theotherjimmy

[teetak01]

I also noticed the exactly same thing yesterday. I copied some defines from git and had something like this in mbed_app.json:

   "macros": ["MACRO1",
               "MACRO2",
+               "MACRO3"],

So I had a + sign there, which I did not notice for a while and got very strange fails in compilation :-)

Maybe mbed-cli could do some validation for critical configuration files?

[theotherjimmy]

Okay guys, mbed tools do report the error, it's just hidden by tonnes of output.
For example:

1. cat mbed_app.json : ,
2. mbed compile

Error parsing './mbed_app.json':
No JSON object could be decoded
Building project mbed-os-example-fat-filesystem (K64F, GCC_ARM)
Scan: .
Scan: FEATURE_LWIP
Scan: FEATURE_COMMON_PAL
Scan: FEATURE_UVISOR
Scan: FEATURE_BLE
Scan: FEATURE_LOWPAN_ROUTER
Scan: FEATURE_ETHERNET_HOST
Scan: FEATURE_NANOSTACK
Scan: FEATURE_THREAD_END_DEVICE
Scan: FEATURE_THREAD_ROUTER
Scan: FEATURE_THREAD_BORDER_ROUTER
Scan: FEATURE_LOWPAN_BORDER_ROUTER
Scan: FEATURE_NANOSTACK_FULL
Scan: FEATURE_LOWPAN_HOST
Scan: FEATURE_STORAGE
Scan: mbed
Scan: env

[theotherjimmy]

I take it that you are requesting that it stops and does not continue.

[theotherjimmy]

See ARMmbed/mbed-os#4098 for a fix.