Add a left-justified width field to log2_work component for a uniform debug.log output #19317

Motivation: It's jarring to watch the output of tail -f ~/btcdata/debug.log scroll by and very frequently see columns not lining up correctly because log2_work somtimes has less precision than 8 digits.

Current display:

2020-06-18T02:54:42Z UpdateTip: new best=0000000000000000107f877e4920643f9fb06090fa7551cd1cdd83b857f520aa height=382038 version=0x00000003 log2_work=83.558653 tx=90953616 date='2015-11-04T17:11:44Z' progress=0.166675 cache=117.6MiB(966410txo)
2020-06-18T02:54:51Z UpdateTip: new best=0000000000000000019a4de585d30d1a8cc13c7a1972d11b4945635c9556acb5 height=382039 version=0x00000003 log2_work=83.55868 tx=90955936 date='2015-11-04T17:19:39Z' progress=0.166679 cache=117.9MiB(968799txo)

Display with this commit:

2020-06-18T02:54:42Z UpdateTip: new best=0000000000000000107f877e4920643f9fb06090fa7551cd1cdd83b857f520aa height=382038 version=0x00000003 log2_work=83.558653 tx=90953616 date='2015-11-04T17:11:44Z' progress=0.166675 cache=117.6MiB(966410txo)
2020-06-18T02:54:51Z UpdateTip: new best=0000000000000000019a4de585d30d1a8cc13c7a1972d11b4945635c9556acb5 height=382039 version=0x00000003 log2_work=83.55868  tx=90955936 date='2015-11-04T17:19:39Z' progress=0.166679 cache=117.9MiB(968799txo)

Concept ACK: as a pure Bitcoin Core console user (-printtoconsole is my interface) the unnecessary column jumping has annoyed me (mildly) for years :)

It is easier to scan for anomalies if the column lengths don't vary unnecessarily.

Warm welcome as a contributor @jamesgmorgan - nice small console UX improvement :)

Possible alternative which will achieve precision to 6 places and thus remove the suggested left-justification (left-justification might theoretically break log parsers):

diff --git a/src/validation.cpp b/src/validation.cpp
index cbbc857fdcfc..971f19240e51 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1271,12 +1271,12 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
     if (!pindexBestInvalid || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
         pindexBestInvalid = pindexNew;
 
-    LogPrintf("%s: invalid block=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
+    LogPrintf("%s: invalid block=%s  height=%d  log2_work=%f  date=%s\n", __func__,
       pindexNew->GetBlockHash().ToString(), pindexNew->nHeight,
       log(pindexNew->nChainWork.getdouble())/log(2.0), FormatISO8601DateTime(pindexNew->GetBlockTime()));
     CBlockIndex *tip = chainActive.Tip();
     assert (tip);
-    LogPrintf("%s:  current best=%s  height=%d  log2_work=%.8g  date=%s\n", __func__,
+    LogPrintf("%s:  current best=%s  height=%d  log2_work=%f  date=%s\n", __func__,
       tip->GetBlockHash().ToString(), chainActive.Height(), log(tip->nChainWork.getdouble())/log(2.0),
       FormatISO8601DateTime(tip->GetBlockTime()));
     CheckForkWarningConditions();
@@ -2245,7 +2245,7 @@ void static UpdateTip(const CBlockIndex *pindexNew, const CChainParams& chainPar
             DoWarning(strWarning);
         }
     }
-    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)", __func__, /* Continued */
+    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%f tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)", __func__, /* Continued */
       pindexNew->GetBlockHash().ToString(), pindexNew->nHeight, pindexNew->nVersion,
       log(pindexNew->nChainWork.getdouble())/log(2.0), (unsigned long)pindexNew->nChainTx,
       FormatISO8601DateTime(pindexNew->GetBlockTime()),

Will give the output:

2020-06-18T02:54:42Z UpdateTip: new best=0000000000000000107f877e4920643f9fb06090fa7551cd1cdd83b857f520aa height=382038 version=0x00000003 log2_work=83.558653 tx=90953616 date='2015-11-04T17:11:44Z' progress=0.166675 cache=117.6MiB(966410txo)
2020-06-18T02:54:51Z UpdateTip: new best=0000000000000000019a4de585d30d1a8cc13c7a1972d11b4945635c9556acb5 height=382039 version=0x00000003 log2_work=83.558680 tx=90955936 date='2015-11-04T17:19:39Z' progress=0.166679 cache=117.9MiB(968799txo)

Isn't there a way to always force 8 digits of precision? I'd slightly prefer appending 0 to space padding.

Edit: oh, I only just read @practicalswift's post in detail, so just %f?

Concept ACK

Really appreciate both the generous welcome and considered and swift responses - thank you 🙏

On reflection, pad-by-0 rather than space is definitely a better refinement to the fix. @practicalswift if I could ask for guidance - would it be preferable if I made a new commit to update this PR or better to rebase+quash first (would be my inclination)?

Concept ACK. Welcome @jamesgmorgan :) I think squash/force-push would be fine here.

ACK c8583022800410afeb75e0154df7290d080d581d -- patch looks great :)

ACK c8583022800410afeb75e0154df7290d080d581d

Tested ACK c8583022800410afeb75e0154df7290d080d581d