Add dry-run flag (#20)

bin/Main.purs

@@ -103,10 +103,15 @@ cliParser =
       versionSource <- versionSourceArg
       changelogFile <- changelogFileArg
       changelogDir <- changelogDirArg
+      dryRun <- dryRunArg
       Arg.flagHelp
-      in Update { github, versionSource, mbToken, changelogFile, changelogDir }
+      in Update { github, versionSource, mbToken, changelogFile, changelogDir, dryRun }
     where
     cmdDesc = "Updates the changelog file with a new releae entry based on files in the changelog directory"
+    dryRunArg = Arg.flag [ "--dry-run" ] desc
+      # Arg.boolean
+      where
+      desc = "Print to stdout what the new section in the changelog file would be"
     githubRepoArg =
       Arg.choose "repo"
         [ map Left remoteArg

src/UpChangelog/Command/Update.purs

@@ -27,6 +27,7 @@ import Data.Tuple (Tuple(..))
 import Data.Version (Version, showVersion)
 import Data.Version as Version
 import Effect.Aff.Class (liftAff)
+import Effect.Class.Console (log)
 import Fetch as Fetch
 import Foreign (unsafeFromForeign)
 import Node.Path (sep)
@@ -43,7 +44,7 @@ import UpChangelog.Utils (breakOn, breakOnEnd, breakOnSpace, commaSeparate, line
 update :: App (cli :: UpdateArgs) Unit
 update = do
   checkFilePaths
-  { cli: { changelogDir, changelogFile } } <- ask
+  { cli: { changelogDir, changelogFile, dryRun } } <- ask
   entries' <- (lines <<< _.stdout) <$> git "ls-tree" [ "--name-only", "HEAD", changelogDir <> sep ]
   let
     readmeFile = Path.concat [ changelogDir, Constants.readmeFile ]
@@ -74,23 +75,27 @@ update = do
     , after: changelogRest
     } <- breakOn (Pattern "\n## ") <$> readTextFile changelogFile
     logDebug $ "Changelog preamble is: \n" <> changelogPreamble
-    writeTextFile changelogFile $
-      changelogPreamble
-        <> "\n## "
-        <> version
-        <> "\n"
-        <> conditionalSection "Breaking changes" breaks
-        <> conditionalSection "New features" features
-        <> conditionalSection "Bugfixes" fixes
-        <> conditionalSection "Other improvements" misc
-        <> conditionalSection "Internal" internal
-        <> changelogRest
-    logInfo $ "Updated changelog file"
+    let
+      newSectionContent =
+        "## "
+          <> version
+          <> "\n"
+          <> conditionalSection "Breaking changes" breaks
+          <> conditionalSection "New features" features
+          <> conditionalSection "Bugfixes" fixes
+          <> conditionalSection "Other improvements" misc
+          <> conditionalSection "Internal" internal
+    if dryRun then do
+      logInfo "Ran using --dry-run flag. Printing what would be the new section to stdout: "
+      log newSectionContent
+    else do
+      writeTextFile changelogFile $ changelogPreamble <> "\n" <> newSectionContent <> changelogRest
+      logInfo $ "Updated changelog file"
 
-    void $ git "add" [ changelogFile ]
-    logDebug $ "Staged changelog file in git"
-    void $ git "rm" entryFiles
-    logDebug $ "Staged the deletion of the changelog entry files in git"
+      void $ git "add" [ changelogFile ]
+      logDebug $ "Staged changelog file in git"
+      void $ git "rm" entryFiles
+      logDebug $ "Staged the deletion of the changelog entry files in git"
   where
   checkFilePaths = do
     { cli: options } <- ask

src/UpChangelog/Types.purs

@@ -29,6 +29,7 @@ type UpdateArgs =
   , mbToken :: Maybe String
   , changelogFile :: FilePath
   , changelogDir :: FilePath
+  , dryRun :: Boolean
   }
 
 type InitArgs =

test/Test/Main.purs

@@ -23,7 +23,7 @@ import Node.Path as Path
 import Node.Process (chdir)
 import Node.Process as Process
 import Test.Spec (SpecT, afterAll, after_, around_, beforeAll, describe, it, sequential)
-import Test.Spec.Assertions (shouldEqual)
+import Test.Spec.Assertions (shouldEqual, shouldNotEqual)
 import Test.Spec.Reporter (consoleReporter)
 import Test.Spec.Runner (defaultConfig, runSpecT)
 import Test.Utils (delDir)
@@ -182,6 +182,16 @@ spec = do
           expectedContent <- readFile correctFile
           logContent `shouldEqual` expectedContent
 
+        it "update - dry-run does not modify file content" \{ repo, correctFile } -> do
+          result <- pursChangelog "update" [ "--repo", repo, "--dry-run" ]
+          when (not $ exitedNormally result) do
+            liftEffect $ throw $ "Result did not exit normally.\n" <> result.stdout <> "\n" <> result.stderr
+          files <- readDir Constants.changelogDir
+          files `shouldNotEqual` [ Constants.readmeFile ]
+          logContent <- readFile Constants.changelogFile
+          expectedContent <- readFile correctFile
+          logContent `shouldNotEqual` expectedContent
+
 withTempDir :: Aff Unit -> Aff Unit
 withTempDir f = do
   originalDir <- liftEffect $ Process.cwd