Add common stanza to completion data

This allows fields and values to be completed correctly inside common
stanzas

Author: VeryMilkyJoe

plugins/hls-cabal-plugin/src/Ide/Plugin/Cabal/Completion/Data.hs

@@ -63,7 +63,7 @@ cabalKeywords =
       ("extra-tmp-files:", filePathCompleter)
     ]
 
--- | Map, containing all stanzas in a cabal file as keys
+-- | Map, containing all stanzas in a cabal file as keys,
 --  and lists of their possible nested keywords as values.
 stanzaKeywordMap :: Map StanzaType (Map KeyWordName Completer)
 stanzaKeywordMap =
@@ -73,6 +73,7 @@ stanzaKeywordMap =
       ("test-suite", testSuiteFields <> libExecTestBenchCommons),
       ("benchmark", benchmarkFields <> libExecTestBenchCommons),
       ("foreign-library", foreignLibraryFields <> libExecTestBenchCommons),
+      ("common", libExecTestBenchCommons),
       ("flag", flagFields),
       ("source-repository", sourceRepositoryFields)
     ]

plugins/hls-cabal-plugin/test/Context.hs

@@ -188,6 +188,9 @@ getContextTests =
             , (Stanza "source-repository" (Just "head"), KeyWord "type:")
             , (Stanza "source-repository" (Just "head"), KeyWord "type:")
             , (Stanza "source-repository" (Just "head"), None)
+            , (Stanza "common" (Just "cabalfmt"), None)
+            , (Stanza "common" (Just "cabalfmt"), None)
+            , (Stanza "common" (Just "cabalfmt"), KeyWord "build-depends:")
             ]
             $ \fileContent posPrefInfo ->
                 callGetContext (cursorPos posPrefInfo) (prefixText posPrefInfo) fileContent
@@ -276,4 +279,10 @@ source-repository head
   location: https://github.com/haskell/haskell-language-server
 
   ^
+common cabalfmt
+
+  ^
+  build-depends: haskell-language-server:hls-cabal-fmt-plugin
+    ^            ^
+  cpp-options: -Dhls_cabalfmt
 |]