Provide more info in SbangPathError to aid CI debugging (#26316)

lib/spack/spack/hooks/sbang.py

@@ -28,9 +28,12 @@ def sbang_install_path():
     """Location sbang should be installed within Spack's ``install_tree``."""
     sbang_root = str(spack.store.unpadded_root)
     install_path = os.path.join(sbang_root, "bin", "sbang")
-    if len(install_path) > shebang_limit:
-        raise SbangPathError(
-            'Install tree root is too long. Spack cannot patch shebang lines.')
+    path_length = len(install_path)
+    if path_length > shebang_limit:
+        msg = ('Install tree root is too long. Spack cannot patch shebang lines'
+               ' when script path length ({0}) exceeds limit ({1}).\n  {2}')
+        msg = msg.format(path_length, shebang_limit, install_path)
+        raise SbangPathError(msg)
     return install_path
 
 

lib/spack/spack/test/sbang.py

@@ -225,3 +225,21 @@ def test_install_sbang(install_mockery):
     # install again and make sure sbang is still fine
     sbang.install_sbang()
     check_sbang_installation()
+
+
+def test_install_sbang_too_long(tmpdir):
+    root = str(tmpdir)
+    num_extend = sbang.shebang_limit - len(root) - len('/bin/sbang')
+    long_path = root
+    while num_extend > 1:
+        add = min(num_extend, 255)
+        long_path = os.path.join(long_path, 'e' * add)
+        num_extend -= add
+    with spack.store.use_store(spack.store.Store(long_path)):
+        with pytest.raises(sbang.SbangPathError) as exc_info:
+            sbang.sbang_install_path()
+
+    err = str(exc_info.value)
+    assert 'root is too long' in err
+    assert 'exceeds limit' in err
+    assert 'cannot patch' in err