Implement `fullCompilerVersion`

Follow-up of https://gitlab.haskell.org/ghc/ghc/-/issues/18403

This MR adds `fullCompilerVersion`, a function that shares the same
backend as the `--numeric-version` GHC flag, exposing a full,
three-digit version datatype.

7 files changed, 44 insertions, 13 deletions

diff --git a/docs/users_guide/phases.rst b/docs/users_guide/phases.rst
index c7a17f6475..af65d613aa 100644
--- a/docs/users_guide/phases.rst
+++ b/docs/users_guide/phases.rst
@@ -336,7 +336,7 @@ defined by your local GHC installation, the following trick is useful:
     .. index::
        single: __GLASGOW_HASKELL_FULL_VERSION__
        This macro exposes the full version string.
-       For instance: ``__FULL_GHC_VERSION__==8.11.0.20200319``.
+       For instance: ``__GLASGOW_HASKELL_FULL_VERSION__==8.11.0.20200319``.
        Its value comes from the ``ProjectVersion`` Autotools variable.
 
 ``__GLASGOW_HASKELL_PATCHLEVEL1__``; \ ``__GLASGOW_HASKELL_PATCHLEVEL2__``
diff --git a/hadrian/src/Rules/Generate.hs b/hadrian/src/Rules/Generate.hs
index 2ac01b4f48..62a7bbebbc 100644
--- a/hadrian/src/Rules/Generate.hs
+++ b/hadrian/src/Rules/Generate.hs
@@ -407,7 +407,7 @@ generateGhcVersionH = do
         , "#define __GLASGOW_HASKELL__ " ++ version
         , "#endif"
         , "#if !defined(__GLASGOW_HASKELL_FULL_VERSION__)"
-        , "#define __GLASGOW_HASKELL_FULL_VERSION__ " ++ fullVersion
+        , "#define __GLASGOW_HASKELL_FULL_VERSION__ \"" ++ fullVersion ++ "\""
         , "#endif"
         , ""]
         ++
diff --git a/includes/ghc.mk b/includes/ghc.mk
index 178bd537ff..cb95d9089b 100644
--- a/includes/ghc.mk
+++ b/includes/ghc.mk
@@ -75,7 +75,7 @@ $$(includes_$1_H_VERSION) : mk/project.mk | $$$$(dir $$$$@)/.
 	@echo "#define __GHCVERSION_H__"                                        >> $$@
 	@echo                                                                   >> $$@
 	@echo "#define __GLASGOW_HASKELL__ $$(ProjectVersionInt)"               >> $$@
-	@echo "#define __GLASGOW_HASKELL_FULL_VERSION__ $$(ProjectVersion)"                 >> $$@
+	@echo "#define __GLASGOW_HASKELL_FULL_VERSION__ \"$$(ProjectVersion)\"" >> $$@
 	@echo                                                                   >> $$@
 	@if [ -n "$$(ProjectPatchLevel1)" ]; then \
 	  echo "#define __GLASGOW_HASKELL_PATCHLEVEL1__ $$(ProjectPatchLevel1)" >> $$@; \
diff --git a/libraries/base/System/Info.hs b/libraries/base/System/Info.hs
index 840a9b5a25..70284d44ef 100644
--- a/libraries/base/System/Info.hs
+++ b/libraries/base/System/Info.hs
@@ -1,12 +1,12 @@
+{-# LANGUAGE CPP  #-}
 {-# LANGUAGE Safe #-}
-{-# LANGUAGE CPP #-}
 
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  System.Info
 -- Copyright   :  (c) The University of Glasgow 2001
 -- License     :  BSD-style (see the file libraries/base/LICENSE)
--- 
+--
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
 -- Portability :  portable
@@ -19,18 +19,18 @@
 -----------------------------------------------------------------------------
 
 module System.Info
-   (
-       os,
-       arch,
-       compilerName,
-       compilerVersion
-   ) where
+  ( os
+  , arch
+  , compilerName
+  , compilerVersion
+  , fullCompilerVersion
+  ) where
 
-import Data.Version
+import           Data.Version (Version (..))
 
 -- | The version of 'compilerName' with which the program was compiled
 -- or is being interpreted.
--- 
+--
 -- ==== __Example__
 -- > ghci> compilerVersion
 -- > Version {versionBranch = [8,8], versionTags = []}
@@ -38,6 +38,22 @@ compilerVersion :: Version
 compilerVersion = Version [major, minor] []
   where (major, minor) = compilerVersionRaw `divMod` 100
 
+-- | The full version of 'compilerName' with which the program was compiled
+-- or is being interpreted. It includes the major, minor, revision and an additional
+-- identifier, generally in the form "<year><month><day>".
+fullCompilerVersion :: Version
+fullCompilerVersion = Version version []
+  where
+    version :: [Int]
+    version = fmap read $ splitVersion __GLASGOW_HASKELL_FULL_VERSION__
+
+splitVersion :: String -> [String]
+splitVersion s =
+  case dropWhile (== '.') s of
+    "" -> []
+    s' -> let (w, s'') = break (== '.') s'
+           in w : splitVersion s''
+
 #include "ghcplatform.h"
 
 -- | The operating system on which the program is running.
diff --git a/libraries/base/tests/SystemInfoTest.hs b/libraries/base/tests/SystemInfoTest.hs
new file mode 100644
index 0000000000..ef8c829df4
--- /dev/null
+++ b/libraries/base/tests/SystemInfoTest.hs
@@ -0,0 +1,13 @@
+{-# LANGUAGE CPP #-}
+module Main where
+
+import           Data.Version (showVersion)
+import           System.Info  (fullCompilerVersion)
+
+main :: IO ()
+main = if textualVersion == macroVersion
+       then putStrLn "Match"
+       else putStrLn $ "[!]" <> textualVersion <> "should be equal to " <> macroVersion
+  where
+    macroVersion   = __GLASGOW_HASKELL_FULL_VERSION__
+    textualVersion = showVersion fullCompilerVersion
diff --git a/libraries/base/tests/SystemInfoTest.stdout b/libraries/base/tests/SystemInfoTest.stdout
new file mode 100644
index 0000000000..1796dc2720
--- /dev/null
+++ b/libraries/base/tests/SystemInfoTest.stdout
@@ -0,0 +1 @@
+Match
diff --git a/libraries/base/tests/all.T b/libraries/base/tests/all.T
index 4a29e8b571..c29b5b3a63 100644
--- a/libraries/base/tests/all.T
+++ b/libraries/base/tests/all.T
@@ -12,6 +12,7 @@ def normalise_quotes (str):
 #--------------------------------------
 # Test functions
 #--------------------------------------
+test('SystemInfoTest', normal, compile_and_run, [''])
 test('readFloat', exit_code(1), compile_and_run, [''])
 test('enumDouble', normal, compile_and_run, [''])
 test('enumRatio', normal, compile_and_run, [''])