# Ghc Tags Compiler Plugin ![](https://github.com/coot/ghc-tags-plugin/workflows/GHC-8.8.3/badge.svg) ![](https://github.com/coot/ghc-tags-plugin/workflows/GHC-8.6.5/badge.svg) A [Ghc Compiler Plugin](https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/extending_ghc.html#compiler-plugins) which generates tags for each compiled module or component. # ● Requirements ``` ghc >= 8.6 ``` # ● Vim configuration By default each generated tags file is put next to the corresponding `*.cabal` package file. If you just have a repo with a cabal file in the main directory `vim` default `tags` setting will work, if you have some modules in subdirectories you will either need to set: ``` :set tags+=*/tags ``` or pass an option to modify where tags are written, see below. # ● Plugin options The plugin accepts an only one option, which is a file path to the tags file. It can be an absolute path or relative (to the `*.cabal` package file rather than `cabal.project` file), for example: ``` -fplugin-opt=Plugin.GhcTags:../tags ``` This is useful if for *cabal packages* which are located in subdirectories. # ● Configuration: Ghc / Cabal / Stack Configuration of this plugin requires some familiarity with `ghc` packages. Check out [documentation](https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.html#packages) to use `-plugin-package` or `-plugin-package-id`. In the examples below we use `-plugin-package=ghc-tags-plugin` but specifying version `-package=ghc-tags-plugin-0.0.0.0` (where `0.0.0.0` is the version you installed), might work better. You can use `ghc-pkg latest ghc-tags-plugin` (likely with appropriate `--package-db` flag) to check which version is available. ## ● Ghc ``` ghc -plugin-package=ghc-tags-plugin -fplugin=Plugin.GhcTags ``` You might also need to pass `-package-db` in which you installed the plugin. ## ● Cabal Install the `ghc-tags-plugin` to cabal store with: ``` cabal install --lib ghc-tags-plugin ``` In `cabal.project.local` file add `package` stanza for every local package : ``` project some-project ghc-options: -package-db=PACKAGE_DB -plugin-package=ghc-tags-plugin -fplugin=Plugin.GhcTags ``` `PACKAGE_DB` is likely to be something like (for `ghc-8.6.5`) (all environment variables must be expanded): ``` ${HOME}/.cabal/store/ghc-8.6.5/package.db ``` or on Windows (note the `""` syntax) ``` "C:\\Users\\USER_NAME\\AppData\\Roaming\\cabal\\store\\ghc-8.6.5\\package.db ``` Note that you can also configure in this way non-local projects. You will likely want to pass `-fplugin-opt=Plugin.GhcTags=PATH` where `PATH` is *an absolute* path to your `tags` file. ## ● Stack This is alternative method, which also could be modified for `cabal` (but it is not as nice as the previous method where you don't need to modify any files checked in vcs). Add `ghc-tags-plugin` to `build-depends` in your `*.cabal` files. (You should hide it behind a cabal flag). And add these lines to `stack.yaml` file: ``` extra-deps: - git: https://github.com/coot/ghc-tags-plugin commit: a841dae7fb9c335101f7fa4187d02687d306f972 test-project: -plugin-package=ghc-tags-plugin -fplugin=Plugin.GhcTags ``` Check out an example [here](https://github.com/coot/ghc-tags-plugin/tree/stack-setup/test-project). ## ● Ghcid If you follow the cabal configuration as above (using `stack` should work too) ``` ghcid --comaand "cabal repl project" ``` will update `tags` file as you modify your project. ## ● Makefile The [Makefile](https://github.com/coot/ghc-tags-plugin/blob/master/Makefile) contains some useful commands, e.g. `install`, `uninstall` or `reinstall` the package in a `package.db` (by default into `cabal` store). This is mostly for development, but it could be useful in other scenarios as well. # ● Exceptions If a `GHC` plugin throws an exception, `GHC` stops. This plugin wraps `IOException`s, to make it obvious that it filed rather than `GHC`. This might mean you misconfigured the plugin (by passing wrong options). The result might look like this: ``` ghc: panic! (the 'impossible' happened) (GHC version 8.6.5 for x86_64-unknown-linux): GhcTagsPluginIOException ../: openFile: inappropriate type (Is a directory) ``` # ● Security implications of compiler plugins Such plugins can: * run arbitrary `IO`; * modify abstract syntax tree in some way; a malicious plugin could change some security parameter in your code exposing a security hole. This plugin only reads & writes to `tags` file (and updates a shared mutable state) as of `IO`, and does not [modify/](https://github.com/coot/ghc-tags-plugin/blob/master/src/Plugin/GhcTags.hs#L95) the syntax tree.