Initial load of multiple home units is slow with lazy component loading

[fendor]

With a default hie.yaml of

cradle:
  cabal:

and "sessionLoading": "multiComponent", the initial load can be incredibly slow, as HLS starts asking for the GhcSession for each module that's currently open in the editor one by one. cabal needs to reconfigure the project each time the set of units to load changes, which can take a non-trivial amount of time on big projects (for example HLS itself).

We get logs such as these:

...
2024-08-16T08:59:17.665247Z | Debug | cabal exec -v0 -- ghc --print-libdir
2024-08-16T08:59:19.499261Z | Debug | cabal exec -v0 -- ghc -package-env=- -ignore-dot-ghci -e Control.Monad.join (Control.Monad.fmap System.IO.putStr System.Environment.getExecutablePath)
2024-08-16T08:59:19.500156Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
...
2024-08-16T08:59:21.104638Z | Debug | Resolving dependencies...
2024-08-16T08:59:25.984647Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T08:59:25.984774Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T08:59:25.984835Z | Debug |  - hls-plugin-api-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.984921Z | Debug |  - ghcide-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.984989Z | Debug |  - hls-test-utils-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.985049Z | Debug |  - ghcide-2.9.0.1 (exe:ghcide) (configuration changed)
2024-08-16T08:59:25.985105Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...
2024-08-16T09:01:06.465845Z | Info | Load cabal cradle using all files (multi-components)
2024-08-16T09:01:08.269128Z | Debug | cabal exec -v0 -- ghc --print-libdir
2024-08-16T09:01:10.157674Z | Debug | cabal exec -v0 -- ghc -package-env=- -ignore-dot-ghci -e Control.Monad.join (Control.Monad.fmap System.IO.putStr System.Environment.getExecutablePath)
2024-08-16T09:01:10.158281Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/ghcide/src/Development/IDE/Plugin/TypeLenses.hs /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
...
2024-08-16T09:01:11.794655Z | Debug | Resolving dependencies...
2024-08-16T09:01:16.890247Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T09:01:16.890352Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T09:01:16.890393Z | Debug |  - ghcide-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:01:16.890695Z | Debug |  - hls-test-utils-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:01:16.890832Z | Debug |  - ghcide-2.9.0.1 (interactive) (exe:ghcide) (configuration changed)
2024-08-16T09:01:16.890906Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...
2024-08-16T09:02:09.749233Z | Debug | cabal exec -v0 -- ghc -package-env=- -ignore-dot-ghci -e Control.Monad.join (Control.Monad.fmap System.IO.putStr System.Environment.getExecutablePath)
2024-08-16T09:02:09.749803Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/hls-plugin-api/src/Ide/Types.hs /home/hugin/Documents/haskell/hls/ghcide/src/Development/IDE/Plugin/TypeLenses.hs /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
...
2024-08-16T09:02:16.081585Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T09:02:16.081704Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T09:02:16.081758Z | Debug |  - hls-plugin-api-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082405Z | Debug |  - ghcide-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082488Z | Debug |  - hls-test-utils-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082542Z | Debug |  - ghcide-2.9.0.1 (interactive) (exe:ghcide) (configuration changed)
2024-08-16T09:02:16.082591Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...
2024-08-16T08:59:19.500156Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
...
2024-08-16T08:59:21.104638Z | Debug | Resolving dependencies...
2024-08-16T08:59:25.984647Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T08:59:25.984774Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T08:59:25.984835Z | Debug |  - hls-plugin-api-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.984921Z | Debug |  - ghcide-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.984989Z | Debug |  - hls-test-utils-2.9.0.1 (lib) (configuration changed)
2024-08-16T08:59:25.985049Z | Debug |  - ghcide-2.9.0.1 (exe:ghcide) (configuration changed)
2024-08-16T08:59:25.985105Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...
2024-08-16T09:01:06.465845Z | Info | Load cabal cradle using all files (multi-components)
2024-08-16T09:01:08.269128Z | Debug | cabal exec -v0 -- ghc --print-libdir
2024-08-16T09:01:10.157674Z | Debug | cabal exec -v0 -- ghc -package-env=- -ignore-dot-ghci -e Control.Monad.join (Control.Monad.fmap System.IO.putStr System.Environment.getExecutablePath)
2024-08-16T09:01:10.158281Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/ghcide/src/Development/IDE/Plugin/TypeLenses.hs /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
2024-08-16T09:01:11.794655Z | Debug | Resolving dependencies...
2024-08-16T09:01:16.890247Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T09:01:16.890352Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T09:01:16.890393Z | Debug |  - ghcide-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:01:16.890695Z | Debug |  - hls-test-utils-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:01:16.890832Z | Debug |  - ghcide-2.9.0.1 (interactive) (exe:ghcide) (configuration changed)
2024-08-16T09:01:16.890906Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...
2024-08-16T09:02:09.749233Z | Debug | cabal exec -v0 -- ghc -package-env=- -ignore-dot-ghci -e Control.Monad.join (Control.Monad.fmap System.IO.putStr System.Environment.getExecutablePath)
2024-08-16T09:02:09.749803Z | Info | cabal --builddir=/home/hugin/.cache/hie-bios/dist-hls-036ebb56a4cc135651b7510a90f3136d v2-repl --with-compiler /home/hugin/.cache/hie-bios/wrapper-b54f81dea4c0e6d1626911c526bc4e36 --with-hc-pkg /home/hugin/.cache/hie-bios/ghc-pkg-99f55999495b863a61d4f15d989eaab4 --keep-temp-files --enable-multi-repl /home/hugin/Documents/haskell/hls/hls-plugin-api/src/Ide/Types.hs /home/hugin/Documents/haskell/hls/ghcide/src/Development/IDE/Plugin/TypeLenses.hs /home/hugin/Documents/haskell/hls/ghcide/test/exe/HighlightTests.hs
...
2024-08-16T09:02:12.266032Z | Debug | eval: fp /home/hugin/Documents/haskell/hls/ghcide/src/Development/IDE/Plugin/TypeLenses.hs
2024-08-16T09:02:12.266264Z | Debug | Finished: codeLens.config Took: 0.00s
2024-08-16T09:02:16.081585Z | Debug | Build profile: -w ghc-9.6.5 -O1
2024-08-16T09:02:16.081704Z | Debug | In order, the following will be built (use -v for more details):
2024-08-16T09:02:16.081758Z | Debug |  - hls-plugin-api-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082405Z | Debug |  - ghcide-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082488Z | Debug |  - hls-test-utils-2.9.0.1 (interactive) (lib) (configuration changed)
2024-08-16T09:02:16.082542Z | Debug |  - ghcide-2.9.0.1 (interactive) (exe:ghcide) (configuration changed)
2024-08-16T09:02:16.082591Z | Debug |  - haskell-language-server-2.9.0.1 (interactive) (test:ghcide-tests) (configuration changed)
...

Note, how this takes three minutes.

Potential solution

Load all modules that are currently open immediately if loadStyle == multiComponent.

[soulomoon]

I suppose, we need a batch loader in hie-bois ? So we can generate deps for all the foi files at once.

[soulomoon]

After implementing a demo for batch load mode and play with it, I’ve encountered a significant challenge: it’s difficult to effectively distribute errors when consulting cradles, as we’re batch loading a large number of new files. 🤔

[fendor]

Yeah, that makes sense... can't we just display the errors in all files that we failed to load?

[soulomoon]

can't we just display the errors in all files that we failed to load?

Yes we can, but the cons is a bit high.
Say we opened x1 .... xn. x1 is the one can't be loaded. But we can load x2 ... xn perfectly.
In batch mode, we are left with x1 ... xn all in loading errors, which is really annoying.

Pertential workaround would be to load these files one by one when batch load failed.
Trade off with load times.

[hellwolf]

Load all modules that are currently open immediately if loadStyle == multiComponent.

Sorry, it is not clear to me what exactly I should do here?