Add test for duplicate environment variables when invoking testsuite

Adds a simple test case that identifies and reports duplicate
environment variables in the Cabal environment.

For issue (#10718)

Author: mpickering

Cabal/src/Distribution/Simple/Bench.hs

@@ -88,7 +88,6 @@ bench args pkg_descr lbi flags = do
               dieWithException verbosity $
                 NoBenchMarkProgram cmd
 
-
             -- Compute the appropriate environment for running the benchmark
             let progDb = LBI.withPrograms lbiForBench
                 pathVar = progSearchPath progDb

Cabal/src/Distribution/Simple/Test/ExeV10.hs

@@ -95,9 +95,12 @@ runTest pkg_descr lbi clbi hpcMarkupInfo flags suite = do
           (testOptions flags)
       tixFile = packageRoot (testCommonFlags flags) </> getSymbolicPath (tixFilePath distPref way (testName'))
 
-  shellEnv <- getFullEnvironment ([("PATH", Just newPath)]
-                                    ++ [("HPCTIXFILE", Just tixFile) | isCoverageEnabled]
-                                    ++ envOverrides)
+  shellEnv <-
+    getFullEnvironment
+      ( [("PATH", Just newPath)]
+          ++ [("HPCTIXFILE", Just tixFile) | isCoverageEnabled]
+          ++ envOverrides
+      )
 
   -- Add (DY)LD_LIBRARY_PATH if needed
   shellEnv' <-

Cabal/src/Distribution/Simple/Test/LibV09.hs

@@ -103,9 +103,12 @@ runTest pkg_descr lbi clbi hpcMarkupInfo flags suite = do
     let opts = map (testOption pkg_descr lbi suite) $ testOptions flags
         tixFile = i $ tixFilePath distPref way testName'
 
-    shellEnv <- getFullEnvironment ([("PATH", Just newPath)]
-                                    ++ [("HPCTIXFILE", Just tixFile) | isCoverageEnabled]
-                                    ++ envOverrides)
+    shellEnv <-
+      getFullEnvironment
+        ( [("PATH", Just newPath)]
+            ++ [("HPCTIXFILE", Just tixFile) | isCoverageEnabled]
+            ++ envOverrides
+        )
     -- Add (DY)LD_LIBRARY_PATH if needed
     shellEnv' <-
       if LBI.withDynExe lbi

cabal-testsuite/PackageTests/DuplicateEnvVars/cabal.out

@@ -0,0 +1 @@
+packages: p

cabal-testsuite/PackageTests/DuplicateEnvVars/cabal.project

@@ -0,0 +1,5 @@
+import Test.Cabal.Prelude
+
+main = cabalTest $ recordMode DoNotRecord $ do
+    res <- cabal' "test" ["all"]
+    assertOutputContains "No duplicate environment variables found" res

cabal-testsuite/PackageTests/DuplicateEnvVars/cabal.test.hs

@@ -0,0 +1,16 @@
+module Main where
+
+import Data.List (group, sort)
+import System.Environment (getEnvironment)
+
+main = do
+    env <- getEnvironment
+    let sortedEnv = sort env
+        duplicates = filter (\g -> length g > 1) $ group $ map fst sortedEnv
+
+    if null duplicates
+        then putStrLn "No duplicate environment variables found."
+        else do
+            putStrLn "Found duplicate environment variables:"
+            mapM_ (\d -> putStrLn $ "  - " ++ head d) duplicates
+            fail "Test failed due to duplicate environment variables"

cabal-testsuite/PackageTests/DuplicateEnvVars/p/Main.hs

@@ -0,0 +1,10 @@
+cabal-version:      3.0
+name:               p
+version:            0.1.0.0
+build-type:         Simple
+
+test-suite env-test
+    default-language: Haskell2010
+    type:             exitcode-stdio-1.0
+    main-is:          Main.hs
+    build-depends:    base

cabal-testsuite/PackageTests/DuplicateEnvVars/p/p.cabal

@@ -0,0 +1,8 @@
+---
+synopsis: "Fix duplicate environment variables in test and benchmark runs"
+packages: [Cabal, cabal-install]
+prs: 10827
+issues: 10718
+---
+
+Cabal no longer creates duplicate environment variables when running test suites, benchmarks, or internal executables. Previously, when setting up the environment for these processes, Cabal would append the overridden environment to the existing environment, creating duplicates of the same variable.