testsuite: Run testsuite dependency calculation before GHC is builtwip/lint-testsuite

The main motivation for this patch is to allow tests to be added to the
testsuite which test things about the source tree without needing to
build GHC. In particular the notes linter can easily start failing and
by integrating it into the testsuite the  process of observing these
changes is caught by normal validation procedures rather than having to
run the linter specially.

With this patch I can run

```
./hadrian/build test --flavour=devel2  --only="uniques"
```

In a clean tree to run the checkUniques linter without having to build
GHC.

Fixes #21029

1 files changed, 20 insertions, 17 deletions

diff --git a/testsuite/driver/runtests.py b/testsuite/driver/runtests.py
index 6858715c7a..f2584e650e 100644
--- a/testsuite/driver/runtests.py
+++ b/testsuite/driver/runtests.py
@@ -274,27 +274,30 @@ def format_path(path):
 
 # On Windows we need to set $PATH to include the paths to all the DLLs
 # in order for the dynamic library tests to work.
-if windows:
-    pkginfo = getStdout([config.ghc_pkg, 'dump'])
-    topdir = config.libdir
+try:
     if windows:
+        pkginfo = getStdout([config.ghc_pkg, 'dump'])
+        topdir = config.libdir
         mingw = os.path.abspath(os.path.join(topdir, '../mingw/bin'))
         mingw = format_path(mingw)
         ghc_env['PATH'] = os.pathsep.join([ghc_env.get("PATH", ""), mingw])
-    for line in pkginfo.split('\n'):
-        if line.startswith('library-dirs:'):
-            path = line.rstrip()
-            path = re.sub('^library-dirs: ', '', path)
-            # Use string.replace instead of re.sub, because re.sub
-            # interprets backslashes in the replacement string as
-            # escape sequences.
-            path = path.replace('$topdir', topdir)
-            if path.startswith('"'):
-                path = re.sub('^"(.*)"$', '\\1', path)
-                path = re.sub('\\\\(.)', '\\1', path)
-
-                path = format_path(path)
-                ghc_env['PATH'] = os.pathsep.join([path, ghc_env.get("PATH", "")])
+        for line in pkginfo.split('\n'):
+            if line.startswith('library-dirs:'):
+                path = line.rstrip()
+                path = re.sub('^library-dirs: ', '', path)
+                # Use string.replace instead of re.sub, because re.sub
+                # interprets backslashes in the replacement string as
+                # escape sequences.
+                path = path.replace('$topdir', topdir)
+                if path.startswith('"'):
+                    path = re.sub('^"(.*)"$', '\\1', path)
+                    path = re.sub('\\\\(.)', '\\1', path)
+
+                    path = format_path(path)
+                    ghc_env['PATH'] = os.pathsep.join([path, ghc_env.get("PATH", "")])
+except FileNotFoundError as err:
+    print (err)
+    print ("Failed to modify PATH for windows... some tests might fail")
 
 testopts_local.x = TestOptions()