Multi Component (#522)

* Multi component support

In this commit we add support for loading multiple components into one
ghcide session.

The current behaviour is that each component is loaded lazily into the
session. When a file from an unrecognised component is loaded, the
cradle is consulted again to get a new set of options for the new
component. This will cause all the currently loaded files to be
reloaded into a new HscEnv which is shared by all the currently known
components. The result of this is that functions such as go-to
definition work between components if they have been loaded into the
same session but you have to open at least one file from each component
before it will work.

Only minimal changes are needed to the internals to ghcide to make the
file searching logic look in include directories for all currently
loaded components. The main changes are in exe/Main.hs which has been
heavily rewritten to avoid shake indirections. A global map is created
which maps a filepath to the HscEnv which should be used to compile it.
When a new component is created this map is completely refreshed so each
path maps to a new

Which paths belong to a componenent is determined by the targets listed
by the cradle. Therefore it is important that each cradle also lists all
the targets for the cradle. There are some other choices here as well
which are less accurate such as mapping via include directories  which
is the aproach that I implemented in haskell-ide-engine.

The commit has been tested so far with cabal and hadrian.

Also deleted the .ghci file which was causing errors during testing and
seemed broken anyway.

Co-authored-by: Alan Zimmerman <[email protected]>
Co-authored-by: fendor <[email protected]>

* Final tweaks?

* Fix 8.4 build

* Add multi-component test

* Fix hlint

* Add cabal to CI images

* Modify path

* Set PATH in the right place (hopefully)

* Always generate interface files and hie files

* Use correct DynFlags in mkImportDirs

You have to use the DynFlags for the file we are currently compiling to
get the right packages in the package db so that lookupPackage doesn't
always fail.

* Revert "Always generate interface files and hie files"

This reverts commit 820aa241890c4498c566e29b0823a803fb2fd297.

* remove traces

* Another test

* lint

* Unset env vars set my stack

* Fix extra-source-files

As usual, stack doesn’t understand Cabal properly and doesn’t seem to
like ** wildcards so I’ve enumerated it manually.

* Unset env locally

Co-authored-by: Alan Zimmerman <[email protected]>
Co-authored-by: fendor <[email protected]>
Co-authored-by: Moritz Kiefer <[email protected]>

Author: 4 people

.azure/linux-stack.yml

@@ -32,7 +32,9 @@ jobs:
       ./fmt.sh
     displayName: "HLint via ./fmt.sh"
   - bash: |
-      sudo apt-get install -y g++ gcc libc6-dev libffi-dev libgmp-dev make zlib1g-dev
+      sudo add-apt-repository ppa:hvr/ghc
+      sudo apt-get update
+      sudo apt-get install -y g++ gcc libc6-dev libffi-dev libgmp-dev make zlib1g-dev cabal-install-3.2
       if ! which stack >/dev/null 2>&1; then
          curl -sSL https://get.haskellstack.org/ | sh
       fi
@@ -41,7 +43,9 @@ jobs:
     displayName: 'stack setup'
   - bash: stack build --only-dependencies --stack-yaml=$STACK_YAML
     displayName: 'stack build --only-dependencies'
-  - bash: stack test --ghc-options=-Werror  --stack-yaml=$STACK_YAML || stack test --ghc-options=-Werror --stack-yaml=$STACK_YAML|| stack test --ghc-options=-Werror --stack-yaml=$STACK_YAML
+  - bash: |
+      export PATH=/opt/cabal/bin:$PATH
+      stack test --ghc-options=-Werror  --stack-yaml=$STACK_YAML || stack test --ghc-options=-Werror --stack-yaml=$STACK_YAML|| stack test --ghc-options=-Werror --stack-yaml=$STACK_YAML
     # ghcide stack tests are flaky, see https://github.com/digital-asset/daml/issues/2606.
     displayName: 'stack test --ghc-options=-Werror'
   - bash: |

.azure/windows-stack.yml

@@ -46,6 +46,7 @@ jobs:
       # Installing happy and alex standalone to avoid error "strip.exe: unable to rename ../*.exe; reason: File exists"
       stack install happy --stack-yaml $STACK_YAML
       stack install alex --stack-yaml $STACK_YAML
+      stack install cabal-install --stack-yaml $STACK_YAML
       stack build --only-dependencies --stack-yaml $STACK_YAML
     displayName: 'stack build --only-dependencies'
   - bash: stack test --no-run-tests --ghc-options=-Werror --stack-yaml $STACK_YAML

.ghci

@@ -25,6 +25,23 @@ There are more details about our approach [in this blog post](https://4ta.uk/p/s
 | Display type and source module of values | hover |
 | Remove redundant imports, replace suggested typos for values and module imports, fill type holes, insert missing type signatures, add suggested ghc extensions  | codeAction (quickfix) |
 
+
+## Limitations to Multi-Component support
+
+`ghcide` supports loading multiple components into the same session so that
+features such as go-to definition work across components. However, there are
+some limitations to this.
+
+1. You will get much better results currently manually specifying the hie.yaml file.
+Until tools like cabal and stack provide the right interface to support multi-component
+projects, it is always advised to specify explicitly how your project partitions.
+2. Cross-component features only work if you have loaded at least one file
+from each component.
+3. There is a known issue where if you have three components, such that A depends on B which depends on C
+then if you load A and C into the session but not B then under certain situations you
+can get strange errors about a type coming from two different places. See [this repo](https://github.com/fendor/ghcide-bad-interface-files) for
+a simple reproduction of the bug.
+
 ## Using it
 
 ### Install `ghcide`
@@ -308,7 +325,7 @@ Now opening a `.hs` file should work with `ghcide`.
 
 ## History and relationship to other Haskell IDE's
 
-The teams behind this project and the [`haskell-ide-engine`](https://github.com/haskell/haskell-ide-engine#readme) have agreed to join forces under the [`haskell-language-server` project](https://github.com/haskell/haskell-language-server), see the [original announcement](https://neilmitchell.blogspot.com/2020/01/one-haskell-ide-to-rule-them-all.html). The technical work is ongoing, with the likely model being that this project serves as the core, while plugins and integrations are kept in the [`haskell-language-server` project](https://github.com/haskell/haskell-language-server). 
+The teams behind this project and the [`haskell-ide-engine`](https://github.com/haskell/haskell-ide-engine#readme) have agreed to join forces under the [`haskell-language-server` project](https://github.com/haskell/haskell-language-server), see the [original announcement](https://neilmitchell.blogspot.com/2020/01/one-haskell-ide-to-rule-them-all.html). The technical work is ongoing, with the likely model being that this project serves as the core, while plugins and integrations are kept in the [`haskell-language-server` project](https://github.com/haskell/haskell-language-server).
 
 The code behind `ghcide` was originally developed by [Digital Asset](https://digitalasset.com/) as part of the [DAML programming language](https://github.com/digital-asset/daml). DAML is a smart contract language targeting distributed-ledger runtimes, based on [GHC](https://www.haskell.org/ghc/) with custom language extensions. The DAML programming language has [an IDE](https://webide.daml.com/), and work was done to separate off a reusable Haskell-only IDE (what is now `ghcide`) which the [DAML IDE then builds upon](https://github.com/digital-asset/daml/tree/master/compiler/damlc). Since that time, there have been various [non-Digital Asset contributors](https://github.com/digital-asset/ghcide/graphs/contributors), in addition to continued investment by Digital Asset. All contributions require a [Contributor License Agreement](https://cla.digitalasset.com/digital-asset/ghcide) that states you license the code under the [Apache License](LICENSE).