b4511e2e2e log: Prefix log messages with function name if -logsourcelocations is set (practicalswift)
Pull request description:
Prefix log messages with function name if `-logfunctionnames` is set.
Yes, exactly like `-logthreadnames` but for function names instead of thread names :)
This is a small developer ergonomics improvement: I've found this to be a cheap/simple way to correlate log output and originating function.
For me it beats the ordinary cycle of 1.) try to figure out a regexp matching the static part of the dynamic log message, 2.) `git grep -E 'Using .* MiB out of .* requested for signature cache'`, 3.) `mcedit filename.cpp` (`openemacs filename.cpp` works too!) and 4.) search for log message and scroll up to find the function name :)
Without any logging parameters:
```
$ src/bitcoind -regtest
2020-08-25T03:29:04Z Using RdRand as an additional entropy source
2020-08-25T03:29:04Z Using 16 MiB out of 32/2 requested for signature cache, able to store 524288 elements
2020-08-25T03:29:04Z Using 16 MiB out of 32/2 requested for script execution cache, able to store 524288 elements
2020-08-25T03:29:04Z Loaded best chain: hashBestChain=0fff88f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e22ff height=0 date=2011-02-02T23:16:42Z progress=1.000000
2020-08-25T03:29:04Z block tree size = 1
2020-08-25T03:29:04Z nBestHeight = 0
2020-08-25T03:29:04Z Imported mempool transactions from disk: 0 succeeded, 0 failed, 0 expired, 0 already there, 0 waiting for initial broadcast
2020-08-25T03:29:04Z 0 addresses found from DNS seeds
```
With `-logthreadnames` and `-logfunctionnames`:
```
$ src/bitcoind -regtest -logthreadnames -logfunctionnames
2020-08-25T03:29:04Z [init] [ReportHardwareRand] Using RdRand as an additional entropy source
2020-08-25T03:29:04Z [init] [InitSignatureCache] Using 16 MiB out of 32/2 requested for signature cache, able to store 524288 elements
2020-08-25T03:29:04Z [init] [InitScriptExecutionCache] Using 16 MiB out of 32/2 requested for script execution cache, able to store 524288 elements
2020-08-25T03:29:04Z [init] [LoadChainTip] Loaded best chain: hashBestChain=0fff88f13cb7b2c71f2a335e3a4fc328bf5beb436012afca590b1a11466e22ff height=0 date=2011-02-02T23:16:42Z progress=1.000000
2020-08-25T03:29:04Z [init] [AppInitMain] block tree size = 1
2020-08-25T03:29:04Z [init] [AppInitMain] nBestHeight = 0
2020-08-25T03:29:04Z [loadblk] [LoadMempool] Imported mempool transactions from disk: 0 succeeded, 0 failed, 0 expired, 0 already there, 0 waiting for initial broadcast
2020-08-25T03:29:04Z [dnsseed] [ThreadDNSAddressSeed] 0 addresses found from DNS seeds
```
ACKs for top commit:
laanwj:
Code review ACK b4511e2e2e
MarcoFalke:
review ACK b4511e2e2e🌃
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b805dbb0b9