Fix setup-no-tix to be hermetic, solves test failures.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

cabal-testsuite/PackageTests/TestSuiteTests/ExeV10/setup-no-tix.cabal.out

@@ -16,5 +16,5 @@ Building test suite 'test-Short' for my-0.1..
 Running 1 test suites...
 Test suite test-Short: RUNNING...
 Test suite test-Short: PASS
-Test suite logged to: setup-no-tix.cabal.dist/work/dist/test/my-0.1-test-Short.log
+Test suite logged to: ../work/dist/test/my-0.1-test-Short.log
 1 of 1 test suites (1 of 1 test cases) passed.

cabal-testsuite/PackageTests/TestSuiteTests/ExeV10/setup-no-tix.out

@@ -11,5 +11,5 @@ Building test suite 'test-Short' for my-0.1..
 Running 1 test suites...
 Test suite test-Short: RUNNING...
 Test suite test-Short: PASS
-Test suite logged to: setup-no-tix.dist/work/dist/test/my-0.1-test-Short.log
+Test suite logged to: ../work/dist/test/my-0.1-test-Short.log
 1 of 1 test suites (1 of 1 test cases) passed.

cabal-testsuite/PackageTests/TestSuiteTests/ExeV10/setup-no-tix.test.hs

 import Test.Cabal.Prelude
 import Distribution.Simple.Hpc
 
--- Ensures that even if -fhpc is manually provided no .tix file is output.
+-- When -fhpc is manually provided, but --enable-coverage is not,
+-- the desired behavior is that we pass on -fhpc to GHC, but do NOT
+-- attempt to do anything with the tix file (i.e., do not change
+-- where it gets output, do not attempt to run hpc on it.)
+--
+-- This was requested in #1945, by a user who wanted to handle the
+-- coverage manually.  Unfortunately, this behavior is (not yet)
+-- documented in the manual. (In fact, coverage is not documented
+-- at all.)
+--
 main = setupAndCabalTest $ do
-    dist_dir <- fmap testDistDir getTestEnv
-    setup_build
-      [ "--enable-tests"
-      , "--ghc-option=-fhpc"
-      , "--ghc-option=-hpcdir"
-      , "--ghc-option=" ++ dist_dir ++ "/hpc/vanilla" ]
-    setup "test" ["test-Short", "--show-details=direct"]
-    lbi <- getLocalBuildInfoM
-    let way = guessWay lbi
-    shouldNotExist $ tixFilePath dist_dir way "test-Short"
+    -- Source copy is necessary as GHC defaults to dumping tix
+    -- file in the CWD, and we do NOT clean it up after the fact.
+    withSourceCopy $ do
+        dist_dir <- fmap testDistDir getTestEnv
+        setup_build
+          [ "--enable-tests"
+          , "--ghc-option=-fhpc"
+          , "--ghc-option=-hpcdir"
+          , "--ghc-option=" ++ dist_dir ++ "/hpc/vanilla" ]
+        setup "test" ["test-Short", "--show-details=direct"]
+        lbi <- getLocalBuildInfoM
+        let way = guessWay lbi
+        shouldNotExist $ tixFilePath dist_dir way "test-Short"