stack takes too long to find out that there is no work to do #1235
Description
Steps to reproduce:
$ cd stack
$ stack build
$ stack build --verbose
Expected:
Stack quickly realizes that there is no work to do and exits.
Actual:
Version 0.1.7.0, Git revision 7264ef6d99f19091f6521722aa620f4b59dba9e3 (dirty) (2415 commits) x86_64
2015-10-26 04:13:13.885705: [debug] Checking for project config at: /home/simon/src/stack/stack.yaml @(stack_FHzONQT9HI3ATX2xQH198L:Stack.Config src/Stack/Config.hs:554:9)
2015-10-26 04:13:13.885916: [debug] Loading project config file stack.yaml @(stack_FHzONQT9HI3ATX2xQH198L:Stack.Config src/Stack/Config.hs:577:13)
2015-10-26 04:13:13.887741: [debug] Run process: ldd /home/simon/.local/bin/stack @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:13.904957: [debug] Trying to decode /home/simon/.stack/build-plan-cache/x86_64-linux/lts-3.7.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:53:5)
2015-10-26 04:13:13.927123: [debug] Success decoding /home/simon/.stack/build-plan-cache/x86_64-linux/lts-3.7.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:62:13)
2015-10-26 04:13:13.92793: [debug] Run process: ghc --info @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:13.993673: [debug] Run process: ghc --numeric-version @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:14.032049: [debug] Run process: ghc-pkg --no-user-package-db field --simple-output Cabal version @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:14.0626: [debug] Run process: ghc-pkg --no-user-package-db list --global @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:14.094419: [debug] Run process: locale -a @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:14.115801: [debug] Checking resolver: lts-3.7 @(stack_FHzONQT9HI3ATX2xQH198L:Stack.Build.Source src/Stack/Build/Source.hs:162:17)
2015-10-26 04:13:14.115972: [debug] Trying to decode /home/simon/.stack/build-plan-cache/x86_64-linux/lts-3.7.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:53:5)
2015-10-26 04:13:14.139067: [debug] Success decoding /home/simon/.stack/build-plan-cache/x86_64-linux/lts-3.7.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:62:13)
2015-10-26 04:13:14.157555: [debug] Trying to decode /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:53:5)
2015-10-26 04:13:14.726689: [debug] Success decoding /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:62:13)
2015-10-26 04:13:14.899557: [debug] Run process: ghc-pkg --global --no-user-package-db dump --expand-pkgroot @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:14.98411: [debug] Run process: ghc-pkg --user --no-user-package-db --package-db /home/simon/.stack/snapshots/x86_64-linux/lts-3.7/7.10.2/pkgdb/ dump --expand-pkgroot @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:15.152178: [debug] Run process: ghc-pkg --user --no-user-package-db --package-db /home/simon/src/stack/.stack-work/install/x86_64-linux/lts-3.7/7.10.2/pkgdb/ dump --expand-pkgroot @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
2015-10-26 04:13:15.197502: [debug] Ignoring package iso8601-time, from (InstalledTo Local,"/home/simon/src/stack/.stack-work/install/x86_64-linux/lts-3.7/7.10.2/pkgdb/"), due to it being unknown to the resolver / extra-deps. @(stack_FHzONQT9HI3ATX2xQH198L:Stack.Build.Installed src/Stack/Build/Installed.hs:189:5)
2015-10-26 04:13:15.198028: [debug] Trying to decode /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:53:5)
2015-10-26 04:13:15.71894: [debug] Success decoding /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:62:13)
2015-10-26 04:13:15.719419: [debug] Trying to decode /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:53:5)
2015-10-26 04:13:16.263889: [debug] Success decoding /home/simon/.stack/indices/Hackage/00-index.cache @(stack_FHzONQT9HI3ATX2xQH198L:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:62:13)
2015-10-26 04:13:16.415685: [debug] Run process: ghc-pkg --no-user-package-db list --global @(stack_FHzONQT9HI3ATX2xQH198L:System.Process.Read src/System/Process/Read.hs:272:3)
This takes about 2.6s on my machine. Among other things stack decodes ~/.stack/indices/Hackage/00-index.cache three times which accounts for about 1.6s.
Is all this work really necessary to discover that there is no building to be done?