More consistently pass --package-db flag to tests

Previously `--package-db` was only passed to test which used the `v2-`
prefix.

Now we pass `--package-db` to things which use the `v2-` prefix, not
things which use the `v1-` prefix and by default assume that unprefixed
commands are v2 commands.

cabal-testsuite/PackageTests/CustomTestCoverage/cabal.out

@@ -4,14 +4,14 @@ Build profile: -w ghc-<GHCVER> -O1
 In order, the following will be built:
  - plain-0.1.0.0 *test (first run)
 Configuring plain-0.1.0.0...
-Preprocessing library for plain-0.1.0.0..
-Building library for plain-0.1.0.0..
-Preprocessing test suite 'test' for plain-0.1.0.0..
-Building test suite 'test' for plain-0.1.0.0..
+Preprocessing library for plain-0.1.0.0...
+Building library for plain-0.1.0.0...
+Preprocessing test suite 'test' for plain-0.1.0.0...
+Building test suite 'test' for plain-0.1.0.0...
 Running 1 test suites...
 Test suite test: RUNNING...
 Test suite test: PASS
-Test suite logged to: cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/test/plain-0.1.0.0-test.log
-Test coverage report written to cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/hpc/vanilla/html/test/hpc_index.html
+Test suite logged to: <ROOT>/cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/test/plain-0.1.0.0-test.log
+Package coverage report written to <ROOT>/cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/hpc/vanilla/html/hpc_index.html
 1 of 1 test suites (1 of 1 test cases) passed.
-Package coverage report written to cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/hpc/vanilla/html/plain-0.1.0.0/hpc_index.html
+Package coverage report written to <ROOT>/cabal.dist/work/./dist/build/<ARCH>/ghc-<GHCVER>/plain-0.1.0.0/hpc/vanilla/html/hpc_index.html

cabal-testsuite/PackageTests/Regression/T9640/cabal.out

@@ -7,8 +7,8 @@ In order, the following will be built:
  - one-custom-0.1.0.0 (lib:one-custom) (requires build)
  - depend-on-custom-with-exe-0.1.0.0 (lib) (first run)
 Configuring one-custom-0.1.0.0...
-Preprocessing library for one-custom-0.1.0.0..
-Building library for one-custom-0.1.0.0..
+Preprocessing library for one-custom-0.1.0.0...
+Building library for one-custom-0.1.0.0...
 Installing library in <PATH>
 Warning: depend-on-custom-with-exe.cabal:16:1: Ignoring trailing fields after sections: "ghc-options"
 Configuring library for depend-on-custom-with-exe-0.1.0.0...

cabal-testsuite/src/Test/Cabal/DecodeShowBuildInfo.hs

@@ -21,7 +21,7 @@ import           System.Exit
 --
 -- Results can be read via 'withPlan', 'buildInfoFile' and 'decodeBuildInfoFile'.
 runShowBuildInfo :: [String] -> TestM ()
-runShowBuildInfo args = cabal "build" ("--enable-build-info":args)
+runShowBuildInfo args = noCabalPackageDb $ cabal "build" ("--enable-build-info":args)
 
 -- | Read 'build-info.json' for a given package and component
 -- from disk and record the content. Helpful for defining test-cases

cabal-testsuite/src/Test/Cabal/Prelude.hs

@@ -316,7 +316,7 @@ cabalGArgs global_args cmd args input = do
           | cmd `elem` ["v2-sdist", "path"]
           = [ "--project-file=" ++ fp | Just fp <- [testCabalProjectFile env] ]
 
-          | cmd == "v2-clean"
+          | cmd == "v2-clean" || cmd == "clean"
           = [ "--builddir", testDistDir env ]
             ++ [ "--project-file=" ++ fp | Just fp <- [testCabalProjectFile env] ]
 
@@ -325,10 +325,14 @@ cabalGArgs global_args cmd args input = do
             , "-j1" ]
             ++ [ "--project-file=" ++ fp | Just fp <- [testCabalProjectFile env] ]
             ++ ["--package-db=" ++ db | Just db <- [testPackageDbPath env]]
+          | "v1-" `isPrefixOf` cmd
+          = [ "--builddir", testDistDir env ]
+            ++ install_args
 
           | otherwise
-          = [ "--builddir", testDistDir env ] ++
-            install_args
+          = [ "--builddir", testDistDir env ]
+            ++ ["--package-db=" ++ db | Just db <- [testPackageDbPath env]]
+            ++ install_args
 
         install_args
           | cmd == "v1-install" || cmd == "v1-build" = [ "-j1" ]