From c25983ab457aed347f104ecc11d1d36c4519bb77 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 12:14:56 -0800
Subject: [PATCH 1/7] cabal-validate: Hide config and tool versions unless
 `--verbose`

`print-config`, `print-tool-versions`, and `time-summary` are no longer
explicit steps, and are instead run implicitly (closes #10570).

`time-summary` is redundant in its current form and is removed. It may
be added back in the future with more detailed output (e.g., which steps
were run, how long did they take individually).

`print-config` and `print-tool-versions` are hidden unless `--verbose`
is given.
---
 cabal-validate/src/Cli.hs  |  7 +---
 cabal-validate/src/Main.hs | 74 +++++++++++++++++---------------------
 cabal-validate/src/Step.hs |  8 +----
 3 files changed, 34 insertions(+), 55 deletions(-)

diff --git a/cabal-validate/src/Cli.hs b/cabal-validate/src/Cli.hs
index 482fb2096b1..55894bd0c9c 100644
--- a/cabal-validate/src/Cli.hs
+++ b/cabal-validate/src/Cli.hs
@@ -179,11 +179,7 @@ resolveOpts opts = do
           then rawSteps opts
           else
             concat
-              [
-                [ PrintConfig
-                , PrintToolVersions
-                , Build
-                ]
+              [ [Build]
               , optional (rawDoctest opts) Doctest
               , optional (rawRunLibTests opts) LibTests
               , optional (rawRunLibSuite opts) LibSuite
@@ -191,7 +187,6 @@ resolveOpts opts = do
               , optional (rawRunCliTests opts && not (rawLibOnly opts)) CliTests
               , optional (rawRunCliSuite opts && not (rawLibOnly opts)) CliSuite
               , optionals (rawSolverBenchmarks opts) [SolverBenchmarksTests, SolverBenchmarksRun]
-              , [TimeSummary]
               ]
 
       targets' =
diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
index 51472ad34a4..09b00b2f8cd 100644
--- a/cabal-validate/src/Main.hs
+++ b/cabal-validate/src/Main.hs
@@ -7,7 +7,7 @@ module Main
   , runStep
   ) where
 
-import Control.Monad (forM_)
+import Control.Monad (forM_, when)
 import qualified Data.Text as T
 import qualified Data.Text.IO as T
 import qualified Data.Text.Lazy as T (toStrict)
@@ -16,9 +16,7 @@ import Data.Version (makeVersion, showVersion)
 import System.FilePath ((</>))
 import System.Process.Typed (proc, readProcessStdout_)
 
-import ANSI (SGR (Bold, BrightCyan, Reset), setSGR)
 import Cli (Compiler (..), HackageTests (..), Opts (..), parseOpts)
-import ClockUtil (diffAbsoluteTime, formatDiffTime, getAbsoluteTime)
 import OutputUtil (printHeader, withTiming)
 import ProcessUtil (timed, timedWithCwd)
 import Step (Step (..), displayStep)
@@ -27,6 +25,8 @@ import Step (Step (..), displayStep)
 main :: IO ()
 main = do
   opts <- parseOpts
+  printConfig opts
+  printToolVersions opts
   forM_ (steps opts) $ \step -> do
     runStep opts step
 
@@ -36,8 +36,6 @@ runStep opts step = do
   let title = displayStep step
   printHeader title
   let action = case step of
-        PrintConfig -> printConfig opts
-        PrintToolVersions -> printToolVersions opts
         Build -> build opts
         Doctest -> doctest opts
         LibTests -> libTests opts
@@ -47,7 +45,6 @@ runStep opts step = do
         CliTests -> cliTests opts
         SolverBenchmarksTests -> solverBenchmarksTests opts
         SolverBenchmarksRun -> solverBenchmarksRun opts
-        TimeSummary -> timeSummary opts
   withTiming (startTime opts) title action
   T.putStrLn ""
 
@@ -139,35 +136,39 @@ timedCabalBin opts package component args = do
 
 -- | Print the configuration for CI logs.
 printConfig :: Opts -> IO ()
-printConfig opts = do
-  putStr $
-    unlines
-      [ "compiler:          "
-          <> compilerExecutable (compiler opts)
-      , "cabal-install:     "
-          <> cabal opts
-      , "jobs:              "
-          <> show (jobs opts)
-      , "steps:             "
-          <> unwords (map displayStep (steps opts))
-      , "Hackage tests:     "
-          <> show (hackageTests opts)
-      , "verbose:           "
-          <> show (verbose opts)
-      , "extra compilers:   "
-          <> unwords (extraCompilers opts)
-      , "extra RTS options: "
-          <> unwords (rtsArgs opts)
-      ]
+printConfig opts =
+  when (verbose opts) $
+    printHeader "Configuration"
+    putStr $
+      unlines
+        [ "compiler:          "
+            <> compilerExecutable (compiler opts)
+        , "cabal-install:     "
+            <> cabal opts
+        , "jobs:              "
+            <> show (jobs opts)
+        , "steps:             "
+            <> unwords (map displayStep (steps opts))
+        , "Hackage tests:     "
+            <> show (hackageTests opts)
+        , "verbose:           "
+            <> show (verbose opts)
+        , "extra compilers:   "
+            <> unwords (extraCompilers opts)
+        , "extra RTS options: "
+            <> unwords (rtsArgs opts)
+        ]
 
 -- | Print the versions of tools being used.
 printToolVersions :: Opts -> IO ()
-printToolVersions opts = do
-  timed opts (compilerExecutable (compiler opts)) ["--version"]
-  timed opts (cabal opts) ["--version"]
+printToolVersions opts =
+  when (verbose opts) $ do
+    printHeader "Tool versions"
+    timed opts (cabal opts) ["--version"]
+    timed opts (compilerExecutable (compiler opts)) ["--version"]
 
-  forM_ (extraCompilers opts) $ \compiler' -> do
-    timed opts compiler' ["--version"]
+    forM_ (extraCompilers opts) $ \compiler' -> do
+      timed opts compiler' ["--version"]
 
 -- | Run the build step.
 build :: Opts -> IO ()
@@ -413,14 +414,3 @@ solverBenchmarksRun opts = do
     , "--packages=Chart-diagrams"
     , "--print-trials"
     ]
-
--- | Print the total time taken so far.
-timeSummary :: Opts -> IO ()
-timeSummary opts = do
-  endTime <- getAbsoluteTime
-  let totalDuration = diffAbsoluteTime endTime (startTime opts)
-  putStrLn $
-    setSGR [Bold, BrightCyan]
-      <> "!!! Validation completed in "
-      <> formatDiffTime totalDuration
-      <> setSGR [Reset]
diff --git a/cabal-validate/src/Step.hs b/cabal-validate/src/Step.hs
index 2636f483a79..801b660f5cc 100644
--- a/cabal-validate/src/Step.hs
+++ b/cabal-validate/src/Step.hs
@@ -11,9 +11,7 @@ import qualified Data.Map.Strict as Map
 
 -- | A step to be run by @cabal-validate@.
 data Step
-  = PrintConfig
-  | PrintToolVersions
-  | Build
+  = Build
   | Doctest
   | LibTests
   | LibSuite
@@ -22,7 +20,6 @@ data Step
   | CliSuite
   | SolverBenchmarksTests
   | SolverBenchmarksRun
-  | TimeSummary
   deriving (Eq, Enum, Bounded, Show)
 
 -- | Get the display identifier for a given `Step`.
@@ -34,8 +31,6 @@ data Step
 displayStep :: Step -> String
 displayStep step =
   case step of
-    PrintConfig -> "print-config"
-    PrintToolVersions -> "print-tool-versions"
     Build -> "build"
     Doctest -> "doctest"
     LibTests -> "lib-tests"
@@ -45,7 +40,6 @@ displayStep step =
     CliSuite -> "cli-suite"
     SolverBenchmarksTests -> "solver-benchmarks-tests"
     SolverBenchmarksRun -> "solver-benchmarks-run"
-    TimeSummary -> "time-summary"
 
 -- | A map from step names to `Steps`.
 --

From ac29d59c76462c5c940fe3dad4a29007b46bfb89 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 12:17:56 -0800
Subject: [PATCH 2/7] cabal-validate: Hide build plan unless `--verbose`

Hide the build plan (listing of local packages and transitive
dependencies) unless `--verbose` is given.
---
 cabal-validate/src/Main.hs | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
index 09b00b2f8cd..e506448a940 100644
--- a/cabal-validate/src/Main.hs
+++ b/cabal-validate/src/Main.hs
@@ -173,24 +173,25 @@ printToolVersions opts =
 -- | Run the build step.
 build :: Opts -> IO ()
 build opts = do
-  printHeader "build (dry run)"
-  timed
-    opts
-    (cabal opts)
-    ( cabalNewBuildArgs opts
-        ++ targets opts
-        ++ ["--dry-run"]
-    )
-
-  printHeader "build (full build plan; cached and to-be-built dependencies)"
-  timed
-    opts
-    "jq"
-    [ "-r"
-    , -- TODO: Maybe use `cabal-plan`? It's a heavy dependency though...
-      ".\"install-plan\" | map(.\"pkg-name\" + \"-\" + .\"pkg-version\" + \" \" + .\"component-name\") | join(\"\n\")"
-    , baseBuildDir opts </> "cache" </> "plan.json"
-    ]
+  when (verbose opts) $ do
+    printHeader "build (dry run)"
+    timed
+      opts
+      (cabal opts)
+      ( cabalNewBuildArgs opts
+          ++ targets opts
+          ++ ["--dry-run"]
+      )
+
+    printHeader "build (full build plan; cached and to-be-built dependencies)"
+    timed
+      opts
+      "jq"
+      [ "-r"
+      , -- TODO: Maybe use `cabal-plan`? It's a heavy dependency though...
+        ".\"install-plan\" | map(.\"pkg-name\" + \"-\" + .\"pkg-version\" + \" \" + .\"component-name\") | join(\"\n\")"
+      , baseBuildDir opts </> "cache" </> "plan.json"
+      ]
 
   printHeader "build (actual build)"
   timed

From 2749de93f72ca774829e44e39591b232021d7466 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 12:31:13 -0800
Subject: [PATCH 3/7] cabal-validate: Add `--quiet`

Doesn't do anything yet.
---
 cabal-validate/src/Cli.hs         | 25 +++++++++++++++++++------
 cabal-validate/src/Main.hs        | 14 +++++++-------
 cabal-validate/src/ProcessUtil.hs | 12 +++++++-----
 3 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/cabal-validate/src/Cli.hs b/cabal-validate/src/Cli.hs
index 55894bd0c9c..70120497926 100644
--- a/cabal-validate/src/Cli.hs
+++ b/cabal-validate/src/Cli.hs
@@ -5,6 +5,8 @@ module Cli
   , HackageTests (..)
   , Compiler (..)
   , VersionParseException (..)
+  , Verbosity (..)
+  , whenVerbose
   )
 where
 
@@ -53,7 +55,7 @@ import Step (Step (..), displayStep, parseStep)
 
 -- | Command-line options, resolved with context from the environment.
 data Opts = Opts
-  { verbose :: Bool
+  { verbosity :: Verbosity
   -- ^ Whether to display build and test output.
   , jobs :: Int
   -- ^ How many jobs to use when running tests.
@@ -116,6 +118,17 @@ data Compiler = Compiler
   }
   deriving (Show)
 
+-- | A verbosity level, for log output.
+data Verbosity
+  = Quiet
+  | Info
+  | Verbose
+  deriving (Show, Eq, Ord)
+
+-- | Run an action only if the `verbosity` is `Verbose` or higher.
+whenVerbose :: Applicative f => Opts -> f () -> f ()
+whenVerbose opts action = when (verbosity opts >= Verbose) action
+
 -- | An `Exception` thrown when parsing @--numeric-version@ output from a compiler.
 data VersionParseException = VersionParseException
   { versionInput :: String
@@ -252,7 +265,7 @@ resolveOpts opts = do
 
   pure
     Opts
-      { verbose = rawVerbose opts
+      { verbosity = rawVerbosity opts
       , jobs = jobs'
       , cwd = cwd'
       , startTime = startTime'
@@ -270,7 +283,7 @@ resolveOpts opts = do
 -- | Literate command-line options as supplied by the user, before resolving
 -- defaults and other values from the environment.
 data RawOpts = RawOpts
-  { rawVerbose :: Bool
+  { rawVerbosity :: Verbosity
   , rawJobs :: Maybe Int
   , rawCompiler :: FilePath
   , rawCabal :: FilePath
@@ -298,14 +311,14 @@ rawOptsParser :: Parser RawOpts
 rawOptsParser =
   RawOpts
     <$> ( flag'
-            True
+            Verbose
             ( short 'v'
                 <> long "verbose"
                 <> help "Always display build and test output"
             )
             <|> flag
-              False
-              False
+              Info
+              Quiet
               ( short 'q'
                   <> long "quiet"
                   <> help "Silence build and test output"
diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
index e506448a940..8791a40705c 100644
--- a/cabal-validate/src/Main.hs
+++ b/cabal-validate/src/Main.hs
@@ -7,7 +7,7 @@ module Main
   , runStep
   ) where
 
-import Control.Monad (forM_, when)
+import Control.Monad (forM_)
 import qualified Data.Text as T
 import qualified Data.Text.IO as T
 import qualified Data.Text.Lazy as T (toStrict)
@@ -16,7 +16,7 @@ import Data.Version (makeVersion, showVersion)
 import System.FilePath ((</>))
 import System.Process.Typed (proc, readProcessStdout_)
 
-import Cli (Compiler (..), HackageTests (..), Opts (..), parseOpts)
+import Cli (Compiler (..), HackageTests (..), Opts (..), parseOpts, whenVerbose)
 import OutputUtil (printHeader, withTiming)
 import ProcessUtil (timed, timedWithCwd)
 import Step (Step (..), displayStep)
@@ -137,7 +137,7 @@ timedCabalBin opts package component args = do
 -- | Print the configuration for CI logs.
 printConfig :: Opts -> IO ()
 printConfig opts =
-  when (verbose opts) $
+  whenVerbose opts $ do
     printHeader "Configuration"
     putStr $
       unlines
@@ -151,8 +151,8 @@ printConfig opts =
             <> unwords (map displayStep (steps opts))
         , "Hackage tests:     "
             <> show (hackageTests opts)
-        , "verbose:           "
-            <> show (verbose opts)
+        , "verbosity:         "
+            <> show (verbosity opts)
         , "extra compilers:   "
             <> unwords (extraCompilers opts)
         , "extra RTS options: "
@@ -162,7 +162,7 @@ printConfig opts =
 -- | Print the versions of tools being used.
 printToolVersions :: Opts -> IO ()
 printToolVersions opts =
-  when (verbose opts) $ do
+  whenVerbose opts $ do
     printHeader "Tool versions"
     timed opts (cabal opts) ["--version"]
     timed opts (compilerExecutable (compiler opts)) ["--version"]
@@ -173,7 +173,7 @@ printToolVersions opts =
 -- | Run the build step.
 build :: Opts -> IO ()
 build opts = do
-  when (verbose opts) $ do
+  whenVerbose opts $ do
     printHeader "build (dry run)"
     timed
       opts
diff --git a/cabal-validate/src/ProcessUtil.hs b/cabal-validate/src/ProcessUtil.hs
index 3e27f5517a1..01ea66e2c1a 100644
--- a/cabal-validate/src/ProcessUtil.hs
+++ b/cabal-validate/src/ProcessUtil.hs
@@ -5,7 +5,7 @@ module ProcessUtil
   ) where
 
 import Control.Exception (throwIO)
-import Control.Monad (unless)
+import Control.Monad (when)
 import Data.ByteString.Lazy (ByteString)
 import qualified Data.ByteString.Lazy as ByteString
 import Data.Text (Text)
@@ -18,7 +18,7 @@ import System.Exit (ExitCode (ExitFailure, ExitSuccess))
 import System.Process.Typed (ExitCodeException (..), proc, readProcess, runProcess)
 
 import ANSI (SGR (BrightBlue, BrightGreen, BrightRed, Reset), setSGR)
-import Cli (Opts (..))
+import Cli (Opts (..), Verbosity (..))
 import ClockUtil (diffAbsoluteTime, formatDiffTime, getAbsoluteTime)
 
 -- | Like `timed`, but runs the command in a given directory.
@@ -62,7 +62,7 @@ timed opts command args = do
       <> setSGR [Reset]
 
   (exitCode, rawStdout, rawStderr) <-
-    if verbose opts
+    if verbosity opts >= Verbose
       then do
         exitCode <- runProcess process
         pure (exitCode, ByteString.empty, ByteString.empty)
@@ -81,7 +81,9 @@ timed opts command args = do
 
   case exitCode of
     ExitSuccess -> do
-      unless (verbose opts) $ do
+      -- Output is captured unless `--verbose` is used, so only print it here
+      -- if `--verbose` _isn't_ used.
+      when (verbosity opts <= Info) $ do
         if hiddenLines <= 0
           then T.putStrLn output
           else
@@ -102,7 +104,7 @@ timed opts command args = do
           <> formatDiffTime totalDuration
           <> setSGR [Reset]
     ExitFailure exitCode' -> do
-      unless (verbose opts) $ do
+      when (verbosity opts <= Info) $ do
         T.putStrLn output
 
       putStrLn $

From acc21faa7e007585143fac35a9ec3007a96ffccb Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 15:56:05 -0800
Subject: [PATCH 4/7] Only capture process output when `--quiet` is used

---
 cabal-validate/src/ProcessUtil.hs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/cabal-validate/src/ProcessUtil.hs b/cabal-validate/src/ProcessUtil.hs
index 01ea66e2c1a..86c5c16e73f 100644
--- a/cabal-validate/src/ProcessUtil.hs
+++ b/cabal-validate/src/ProcessUtil.hs
@@ -62,7 +62,7 @@ timed opts command args = do
       <> setSGR [Reset]
 
   (exitCode, rawStdout, rawStderr) <-
-    if verbosity opts >= Verbose
+    if verbosity opts > Quiet
       then do
         exitCode <- runProcess process
         pure (exitCode, ByteString.empty, ByteString.empty)
@@ -81,9 +81,9 @@ timed opts command args = do
 
   case exitCode of
     ExitSuccess -> do
-      -- Output is captured unless `--verbose` is used, so only print it here
-      -- if `--verbose` _isn't_ used.
-      when (verbosity opts <= Info) $ do
+      -- Output is captured when `--quiet` is used, so only print it here
+      -- if `--quiet` _isn't_ used.
+      when (verbosity opts > Quiet) $ do
         if hiddenLines <= 0
           then T.putStrLn output
           else

From 358fd1462086eb2f167654d936a38f59df553a80 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 15:56:29 -0800
Subject: [PATCH 5/7] Only `--hide-successes` when `--quiet` is used

---
 cabal-validate/src/Cli.hs | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/cabal-validate/src/Cli.hs b/cabal-validate/src/Cli.hs
index 70120497926..6a3a33c8f40 100644
--- a/cabal-validate/src/Cli.hs
+++ b/cabal-validate/src/Cli.hs
@@ -241,7 +241,12 @@ resolveOpts opts = do
           else "cabal.validate.project"
 
       tastyArgs' =
-        optional (rawTastyHideSuccesses opts) "--hide-successes"
+        maybe
+          -- If neither `--hide-successes` or `--no-hide-successes` was given, then
+          -- only `--hide-successes` if `--quiet` is given.
+          (optional (rawVerbosity opts <= Quiet) "--hide-successes")
+          (\hideSuccesses -> optional hideSuccesses "--hide-successes")
+          (rawTastyHideSuccesses opts)
           ++ maybe
             []
             (\tastyPattern -> ["--pattern", tastyPattern])
@@ -290,7 +295,7 @@ data RawOpts = RawOpts
   , rawExtraCompilers :: [FilePath]
   , rawTastyPattern :: Maybe String
   , rawTastyArgs :: [String]
-  , rawTastyHideSuccesses :: Bool
+  , rawTastyHideSuccesses :: Maybe Bool
   , rawDoctest :: Bool
   , rawSteps :: [Step]
   , rawListSteps :: Bool
@@ -361,8 +366,7 @@ rawOptsParser =
               <> help "Extra arguments to pass to Tasty test suites"
           )
       )
-    <*> boolOption
-      True
+    <*> maybeBoolOption
       "hide-successes"
       ( help "Do not print tests that passed successfully"
       )
@@ -444,6 +448,12 @@ boolOption :: Bool -> String -> Mod FlagFields Bool -> Parser Bool
 boolOption defaultValue trueName =
   boolOption' defaultValue trueName ("no-" <> trueName)
 
+-- | Like `boolOption`, but can tell if an option was passed or not.
+maybeBoolOption :: String -> Mod FlagFields (Maybe Bool) -> Parser (Maybe Bool)
+maybeBoolOption trueName modifiers =
+  flag' (Just True) (modifiers <> long trueName)
+    <|> flag Nothing (Just False) (modifiers <> hidden <> long ("no-" <> trueName))
+
 -- | Full `Parser` for `RawOpts`, which includes a @--help@ argument and
 -- information about the program.
 fullRawOptsParser :: ParserInfo RawOpts

From 80a656b4610e78b9c96ed85a7a14419212f5f767 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Wed, 20 Nov 2024 16:06:34 -0800
Subject: [PATCH 6/7] GHA: Remove `print-config` and `print-tool-versions`

These are no longer explicit steps and will be printed at the start of
each `validate.sh` run individually. (This is more accurate because
flags like `--with-cabal` and `--extra-hc`, which are only used in some
steps, influence the configuration and tool versions in use.)
---
 .github/workflows/validate.yml | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 786a3b9902d..7e581555a35 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -192,12 +192,6 @@ jobs:
           fi
           echo "FLAGS=$FLAGS" >> "$GITHUB_ENV"
 
-      - name: Validate print-config
-        run: sh validate.sh $FLAGS -s print-config
-
-      - name: Validate print-tool-versions
-        run: sh validate.sh $FLAGS -s print-tool-versions
-
       - name: Validate build
         run: sh validate.sh $FLAGS -s build
 
@@ -454,9 +448,6 @@ jobs:
       - name: Untar the cabal executable
         run: tar -xzf "./cabal-head/cabal-head-${{ runner.os }}-$CABAL_ARCH.tar.gz" -C cabal-head
 
-      - name: print-config using cabal HEAD
-        run: sh validate.sh ${{ env.COMMON_FLAGS }} --with-cabal ./cabal-head/cabal -s print-config
-
       # We dont use cache to force a build with a fresh store dir and build dir
       # This way we check cabal can build all its dependencies
       - name: Build using cabal HEAD

From 86c452560c4e2b386e491e266666ed162673a785 Mon Sep 17 00:00:00 2001
From: Rebecca Turner <rbt@sent.as>
Date: Tue, 10 Dec 2024 11:05:05 -0800
Subject: [PATCH 7/7] Line-buffer stdout and stderr

I though this was the default, but apparently not! This seems to fix
output ordering issues.

Noticed here: https://github.com/haskell/cabal/pull/10573#issuecomment-2532562835
---
 cabal-validate/src/Main.hs | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
index 8791a40705c..7164f3f8cc4 100644
--- a/cabal-validate/src/Main.hs
+++ b/cabal-validate/src/Main.hs
@@ -14,6 +14,7 @@ import qualified Data.Text.Lazy as T (toStrict)
 import qualified Data.Text.Lazy.Encoding as T (decodeUtf8)
 import Data.Version (makeVersion, showVersion)
 import System.FilePath ((</>))
+import System.IO (BufferMode (LineBuffering), hSetBuffering, stderr, stdout)
 import System.Process.Typed (proc, readProcessStdout_)
 
 import Cli (Compiler (..), HackageTests (..), Opts (..), parseOpts, whenVerbose)
@@ -24,6 +25,18 @@ import Step (Step (..), displayStep)
 -- | Entry-point for @cabal-validate@.
 main :: IO ()
 main = do
+  -- You'd _think_ that line-buffering for stdout and stderr would be the
+  -- default behavior, and the documentation makes gestures at it, but it
+  -- appears to not be the case!
+  --
+  -- > For most implementations, physical files will normally be
+  -- > block-buffered and terminals will normally be line-buffered.
+  --
+  -- However, on GitHub Actions and on my machine (macOS M1), adding these
+  -- lines makes output appear in the correct order!
+  hSetBuffering stdout LineBuffering
+  hSetBuffering stderr LineBuffering
+
   opts <- parseOpts
   printConfig opts
   printToolVersions opts
@@ -103,11 +116,11 @@ cabalListBinArgs opts = "list-bin" : cabalArgs opts
 cabalListBin :: Opts -> String -> IO FilePath
 cabalListBin opts target = do
   let args = cabalListBinArgs opts ++ [target]
-  stdout <-
+  stdout' <-
     readProcessStdout_ $
       proc (cabal opts) args
 
-  pure (T.unpack $ T.strip $ T.toStrict $ T.decodeUtf8 stdout)
+  pure (T.unpack $ T.strip $ T.toStrict $ T.decodeUtf8 stdout')
 
 -- | Get the RTS arguments for invoking test suites.
 --