Fix commercialhaskell#6696 Add stack config build-files

Also makes minor correction to in-app documentation for other `stack config` commands.

Author: mpilgrem

ChangeLog.md

@@ -12,6 +12,10 @@ Behavior changes:
 
 Other enhancements:
 
+* Add the `stack config build-files` command to generate (when applicable) a
+  Cabal file from a package description in the Hpack format and/or a lock file
+  for Stack's project-level configuration, without taking any other build steps.
+
 Bug fixes:
 
 ## v3.5.0.1 (release candidate) - 2025-03-15

doc/commands/config_command.md

@@ -6,13 +6,32 @@
 stack config COMMAND
 
 Available commands:
-  env                      Print environment variables for use in a shell
-  set                      Sets a key in configuration file to value
+  build-files              Generate (when applicable) a Cabal file from a
+                           package description in the Hpack format and/or a lock
+                           file for Stack's project-level configuration.
+  env                      Print environment variables for use in a shell.
+  set                      Set a key in a configuration file to value.
 ~~~
 
 The `stack config` commands provide assistance with accessing or modifying
 Stack's configuration. See `stack config` for the available commands.
 
+## The `stack config build-files` command
+
+~~~text
+stack config build-files
+~~~
+
+`stack config build-files` generates (when applicable):
+
+* a Cabal file from a package description in the Hpack format (`package.yaml`);
+  and/or
+
+* a [lock file](../topics/lock_files.md) for Stack's project-level
+  configuration (by default, `stack.yaml`);
+
+without taking any other build steps.
+
 ## The `stack config env` command
 
 ~~~text

doc/topics/lock_files.md

@@ -10,6 +10,7 @@ few problems with making this work:
 * Entering all of the information to fully provide reproducibility is tedious.
   This would include things like Hackage revisions, hashes of remote tarballs,
   etc. Users don't want to enter this information.
+
 * Many operations in Stack rely upon a "snapshot hash," which transitively
   includes the completed information for all of these dependencies. If any of
   that information is missing when parsing the `stack.yaml` file or snapshot
@@ -184,3 +185,11 @@ Subject to Stack's
 [`--lock-file`](../configure/global_flags.md#-lock-file-option) option, that new
 lock file is compared against the one on disk and, if there are any differences,
 written out to the disk.
+
+## `stack config build-files` command
+
+The
+[`stack config build-files`](../commands/config_command.md#the-stack-config-build-files-command)
+loads a project-level configuration file (see above) without taking any other
+build steps (other than generating, when applicable, a Cabal file from a package
+description in the Hpack format).

src/Stack/CLI.hs

@@ -26,7 +26,11 @@ import           RIO.Process ( withProcessContextNoLogging )
 import           Stack.Build ( buildCmd )
 import           Stack.BuildInfo ( hpackVersion, versionString' )
 import           Stack.Clean ( CleanCommand (..), cleanCmd )
-import           Stack.ConfigCmd as ConfigCmd
+import           Stack.ConfigCmd
+                   ( cfgCmdBuildFiles, cfgCmdBuildFilesName, cfgCmdEnv
+                   , cfgCmdEnvName, configCmdEnvParser, cfgCmdName, cfgCmdSet
+                   , cfgCmdSetName, configCmdSetParser
+                   )
 import           Stack.Constants
                    ( globalFooter, osIsWindows, relFileStack, relFileStackDotExe
                    , stackProgName
@@ -72,7 +76,9 @@ import qualified Stack.Path ( path )
 import           Stack.Prelude
 import           Stack.Query ( queryCmd )
 import           Stack.Runners
-                   ( ShouldReexec (..), withConfig, withDefaultEnvConfig )
+                   ( ShouldReexec (..), withBuildConfig, withConfig
+                   , withDefaultEnvConfig
+                   )
 import           Stack.SDist ( sdistCmd )
 import           Stack.Script ( ScriptOpts (..), scriptCmd )
 import           Stack.SetupCmd ( setupCmd )
@@ -224,19 +230,28 @@ commandLineHandler currentDir progName mExecutablePath isInterpreter =
     (cleanOptsParser Clean)
 
   config = addSubCommands'
-      ConfigCmd.cfgCmdName
+      cfgCmdName
         "Subcommands for accessing and modifying configuration values."
         ( do
             addCommand'
-              ConfigCmd.cfgCmdSetName
-              "Sets a key in configuration file to value."
+              cfgCmdSetName
+              "Set a key in a configuration file to value."
               (withConfig NoReexec . cfgCmdSet)
               configCmdSetParser
             addCommandWithLocalInstallRootFooter
-              ConfigCmd.cfgCmdEnvName
+              cfgCmdEnvName
               "Print environment variables for use in a shell."
               (withConfig YesReexec . withDefaultEnvConfig . cfgCmdEnv)
               configCmdEnvParser
+            addCommand'
+              cfgCmdBuildFilesName
+              "Generate (when applicable) a Cabal file from a package \
+              \ description in the Hpack format and/or a lock file for Stack's \
+              \project-level configuration."
+              -- It is withBuildConfig that yields the desired actions;
+              -- cfgCmdBuildFiles itself yields nothing of interest.
+              (withConfig YesReexec . withBuildConfig . cfgCmdBuildFiles)
+              (pure ())
         )
 
   docker = addSubCommands'

src/Stack/ConfigCmd.hs

@@ -13,6 +13,8 @@ module Stack.ConfigCmd
   , configCmdEnvParser
   , cfgCmdEnv
   , cfgCmdEnvName
+  , cfgCmdBuildFiles
+  , cfgCmdBuildFilesName
   , cfgCmdName
   ) where
 
@@ -40,6 +42,7 @@ import           Stack.Config
                    )
 import           Stack.Constants ( stackDotYaml )
 import           Stack.Prelude
+import           Stack.Types.BuildConfig ( BuildConfig )
 import           Stack.Types.Config ( Config (..), HasConfig (..) )
 import           Stack.Types.ConfigMonoid
                    ( configMonoidInstallGHCName
@@ -307,6 +310,9 @@ cfgCmdSetName = "set"
 cfgCmdEnvName :: String
 cfgCmdEnvName = "env"
 
+cfgCmdBuildFilesName :: String
+cfgCmdBuildFilesName = "build-files"
+
 configCmdSetParser :: OA.Parser ConfigCmdSet
 configCmdSetParser =
   OA.hsubparser $
@@ -461,3 +467,8 @@ cfgCmdEnv es = do
       escape '\'' = "'\"'\"'"
       escape c = T.singleton c
   putBuilder $ Map.foldMapWithKey toLine actions
+
+-- | This function takes no settings and yields no action of interest. It is
+-- 'withBuildConfig' that yields the desired actions.
+cfgCmdBuildFiles :: () -> RIO BuildConfig ()
+cfgCmdBuildFiles () = pure ()