fix: detect ghc-debug support more accurately, checking hledger-lib also

doc/DEVFAQ.md

@@ -55,18 +55,25 @@ $ cabal install all:exes
 ### How do I build/run with ghc-debug support ?
 
 ```cli
-$ stack build --flag hledger:ghcdebug --flag hledger-ui:ghcdebug --flag hledger-web:ghcdebug
+$ stack build --flag hledger-lib:ghcdebug --flag hledger:ghcdebug --flag hledger-ui:ghcdebug --flag hledger-web:ghcdebug
 ```
-You can check it in the --version output, which should mention "ghc-debug":
+Use --flag to enable `ghcdebug` for hledger-lib and any of the executables you want to build, as above.
+You might need to stop background builders like HLS while you do this, to avoid a fight over the build flag
+(in VS Code, do Haskell: Stop Haskell LSP Server).
+
+Your --version output should now say "supports ghc-debug":
 ```
 $ stack exec -- hledger --version
 ```
-With such a build, you can enable the ghc-debug listener by running hledger with a negative --debug level. Eg:
+
+When a hledger executable supports ghc-debug, you can enable the ghc-debug listener by running with a negative --debug level. Eg:
 ```cli
-$ hledger ... --debug=-1    # run normally, while also listening for ghc-debug commands
+$ hledger CMD --debug=-1    # run normally, while also listening for ghc-debug commands
-$ hledger ... --debug=-2    # pause for ghc-debug commands at program start
+$ hledger CMD --debug=-2    # pause for ghc-debug commands at program start
-$ hledger ... --debug=-3    # pause for ghc-debug commands at program end
+$ hledger CMD --debug=-3    # pause for ghc-debug commands at program end
 ```
-Then you can pause/resume hledger's execution and inspect memory and profile information
+You should see "Starting ghc-debug on socket: ..." output.
-with the interactive `ghc-debug-brick` client,
+
-or extract specific information with a custom ghc-debug script.
+Then in another window, run the interactive `ghc-debug-brick` client, select the running hledger process,
+and explore memory/profile information, resume/pause execution, etc.
+Or you can write a custom ghc-debug-client script to extract specific information.

hledger-lib/Hledger/Utils/Debug.hs

@@ -163,6 +163,7 @@ module Hledger.Utils.Debug (
   ,dbg9With
 
   -- * Utilities
+  ,ghcDebugSupportedInLib
   ,GhcDebugMode(..)
   ,ghcDebugMode
   ,withGhcDebug'
@@ -238,20 +239,28 @@ data GhcDebugMode =
   | GDPauseAtStart
   | GDPauseAtEnd
   -- keep synced with ghcDebugMode
-  deriving (Eq,Ord)
+  deriving (Eq,Ord,Show)
+
+-- | Is the hledger-lib package built with ghc-debug support ?
+ghcDebugSupportedInLib :: Bool
+ghcDebugSupportedInLib =
+#ifdef GHCDEBUG
+  True
+#else
+  False
+#endif
 
 -- | Should the program open a socket allowing control by ghc-debug-brick or similar ghc-debug client ?
 -- See GhcDebugMode.
 ghcDebugMode :: GhcDebugMode
 ghcDebugMode =
   case debugLevel of
-    -- keep synced with GhcDebugMode
+    _ | not ghcDebugSupportedInLib -> GDNotSupported
-#ifdef GHCDEBUG
     (-1) -> GDNoPause
     (-2) -> GDPauseAtStart
     (-3) -> GDPauseAtEnd
-#endif
     _    -> GDDisabled
+    -- keep synced with GhcDebugMode
 
 -- | When ghc-debug support has been built into the program and enabled at runtime with --debug=-N,
 -- this calls ghc-debug's withGhcDebug; otherwise it's a no-op.

hledger-lib/package.yaml

@@ -85,11 +85,6 @@ dependencies:
 - extra >=1.6.3
 - Glob >= 0.9
 
-when:
-- condition: (!(os(windows)))
-  dependencies:
-  - pager >=0.1.1.0
-
 ghc-options:
 - -Wall
 - -Wno-incomplete-uni-patterns
@@ -98,6 +93,21 @@ ghc-options:
 - -Wno-type-defaults
 - -Wno-unused-do-bind
 
+flags:
+  ghcdebug:
+    description: Build with support for attaching a ghc-debug client
+    default: false
+    manual:  true
+
+when:
+- condition: (!(os(windows)))
+  dependencies:
+  - pager >=0.1.1.0
+- condition: (flag(ghcdebug))
+  cpp-options: -DGHCDEBUG
+  dependencies:
+  - ghc-debug-stub >=0.6.0.0 && <0.7
+
 source-dirs: 
 #- other/ledger-parse
 - .

hledger/Hledger/Cli/Version.hs

@@ -18,7 +18,7 @@ import System.Info (os, arch)
 import Data.List (intercalate)
 import Data.Maybe (fromMaybe)
 
-import Hledger.Utils (splitAtElement)
+import Hledger.Utils (ghcDebugSupportedInLib, splitAtElement)
 
 type ProgramName    = String
 type PackageVersion = String
@@ -38,9 +38,9 @@ packageversion =
 packagemajorversion :: PackageVersion
 packagemajorversion = intercalate "." $ take 2 $ splitAtElement '.' packageversion
 
--- | Given possible git state info from the build directory (or an error message, which is ignored),
+-- | Given possible git state info from the build directory (or a git error, which is ignored),
--- the name of a program (executable) in the currently building package,
+-- and the ghcdebug build flag, executable name and package version for the package being built,
--- and the package's version, make a complete version string. Here is the logic:
+-- make the best version string we can. Here is the logic:
 -- 
 -- * Program name, OS and architecture are always shown.
 -- * The package version is always shown.
@@ -50,7 +50,8 @@ packagemajorversion = intercalate "." $ take 2 $ splitAtElement '.' packageversi
 -- * (TODO, requires adding --match support to githash:
 --   If there are tags matching THISPKG-[0-9]*, the latest one is used to calculate patch level
 --   (number of commits since tag), and if non-zero, it and the branch name are shown.)
--- * If the ghcdebug build flag was enabled, "ghc-debug support" is shown.
+-- * If the ghcdebug build flag was enabled for the package being built, and for hledger-lib (both are needed),
+--   "ghc-debug support" is shown.
 --
 -- Some example outputs:
 --
@@ -70,10 +71,10 @@ packagemajorversion = intercalate "." $ take 2 $ splitAtElement '.' packageversi
 -- so output should be suitable for all of those.
 --
 versionStringWith :: Either String GitInfo -> Bool -> ProgramName -> PackageVersion -> VersionString
-versionStringWith egitinfo ghcdebug progname packagever =
+versionStringWith egitinfo ghcDebugSupportedInThisPackage progname packagever =
   concat $
     [ progname , " " , version , ", " , os' , "-" , arch ]
-    ++ [ " with ghc-debug support" | ghcdebug ]
+    ++ [ " with ghc-debug support" | ghcDebugSupportedInThisPackage && ghcDebugSupportedInLib ]
   where
     os' | os == "darwin"  = "mac"
         | os == "mingw32" = "windows"