Merge pull request #5731 from mpilgrem/fix5713

Fix #5713 Don't assume unified coverage report redundant if only one *.tix file

Author: NorfairKing

ChangeLog.md

@@ -11,6 +11,11 @@ Major changes:
 
 Behavior changes:
 
+* `stack build --coverage` will generate a unified coverage report, even if
+  there is only one `*.tix` file, in case a package has tested the library of
+  another package that has not tested its own library. See
+  [#5713](https://github.com/commercialhaskell/stack/issues/5713)
+
 Other enhancements:
 
 * Bump to `hpack-0.35.0`.

src/Stack/Coverage.hs

@@ -288,10 +288,25 @@ generateHpcUnifiedReport = do
     extraTixFiles <- findExtraTixFiles
     let tixFiles = tixFiles0  ++ extraTixFiles
         reportDir = outputDir </> relDirCombined </> relDirAll
-    if length tixFiles < 2
-        then logInfo $
-            (if null tixFiles then "No tix files" else "Only one tix file") <>
-            " found in " <>
+-- Previously, the test below was:
+--
+--  if length tixFiles < 2
+--      then logInfo $
+--          (if null tixFiles then "No tix files" else "Only one tix file") <>
+--          " found in " <>
+--          fromString (toFilePath outputDir) <>
+--          ", so not generating a unified coverage report."
+--      else ...
+--
+-- However, a single *.tix file does not necessarily mean that a unified
+-- coverage report is redundant. For example, one package may test the library
+-- of another package that does not test its own library. See
+-- https://github.com/commercialhaskell/stack/issues/5713
+--
+-- As an interim solution, a unified coverage report will always be produced
+-- even if may be redundant in some circumstances.
+    if null tixFiles
+        then logInfo $ "No tix files found in " <>
             fromString (toFilePath outputDir) <>
             ", so not generating a unified coverage report."
         else do