style: simplify arguments with `--tool TOOL` and `--skip TOOL`

`spack style` tests were annoyingly brittle because we could not easily be
specific about which tools to run (we had to use `--no-black`, `--no-isort`,
`--no-flake8`, and `--no-mypy`). We should be able to specify what to run OR
what to skip.

Now you can run, e.g.:

    spack style --tool black,flake8

or:

    spack style --skip black,isort

- [x] Remove  `--no-black`, `--no-isort`, `--no-flake8`, and `--no-mypy` args.
- [x] Add `--tool TOOL` argument.
- [x] Add `--skip TOOL` argument.
- [x] Allow either `--tool black --tool flake8` or `--tool black,flake8` syntax.

3 files changed, 69 insertions, 59 deletions

diff --git a/lib/spack/spack/cmd/style.py b/lib/spack/spack/cmd/style.py
index 3d24228a54..dc4426c8b9 100644
--- a/lib/spack/spack/cmd/style.py
+++ b/lib/spack/spack/cmd/style.py
@@ -46,7 +46,8 @@ exclude_directories = [
 
 #: Order in which tools should be run. flake8 is last so that it can
 #: double-check the results of other tools (if, e.g., --fix was provided)
-#: The list maps an executable name to a spack spec needed to install it.
+#: The list maps an executable name to a method to ensure the tool is
+#: bootstrapped or present in the environment.
 tool_order = [
     ("isort", spack.bootstrap.ensure_isort_in_path_or_raise),
     ("mypy", spack.bootstrap.ensure_mypy_in_path_or_raise),
@@ -54,6 +55,9 @@ tool_order = [
     ("flake8", spack.bootstrap.ensure_flake8_in_path_or_raise),
 ]
 
+#: list of just the tool names -- for argparse
+tool_names = [k for k, _ in tool_order]
+
 #: tools we run in spack style
 tools = {}
 
@@ -180,35 +184,27 @@ def setup_parser(subparser):
         help="format automatically if possible (e.g., with isort, black)",
     )
     subparser.add_argument(
-        "--no-isort",
-        dest="isort",
-        action="store_false",
-        help="do not run isort (default: run isort if available)",
-    )
-    subparser.add_argument(
-        "--no-flake8",
-        dest="flake8",
-        action="store_false",
-        help="do not run flake8 (default: run flake8 or fail)",
-    )
-    subparser.add_argument(
-        "--no-mypy",
-        dest="mypy",
-        action="store_false",
-        help="do not run mypy (default: run mypy if available)",
-    )
-    subparser.add_argument(
-        "--no-black",
-        dest="black",
-        action="store_false",
-        help="run black if available (default: run black if available)",
-    )
-    subparser.add_argument(
         "--root",
         action="store",
         default=None,
         help="style check a different spack instance",
     )
+
+    tool_group = subparser.add_mutually_exclusive_group()
+    tool_group.add_argument(
+        "-t",
+        "--tool",
+        action="append",
+        help="specify which tools to run (default: %s)" % ",".join(tool_names),
+    )
+    tool_group.add_argument(
+        "-s",
+        "--skip",
+        metavar="TOOL",
+        action="append",
+        help="specify tools to skip (choose from %s)" % ",".join(tool_names),
+    )
+
     subparser.add_argument("files", nargs=argparse.REMAINDER, help="specific files to check")
 
 
@@ -233,8 +229,8 @@ def rewrite_and_print_output(
         print(line)
 
 
-def print_style_header(file_list, args):
-    tools = [tool for tool, _ in tool_order if getattr(args, tool)]
+def print_style_header(file_list, args, selected):
+    tools = [tool for tool in tool_names if tool in selected]
     tty.msg("Running style checks on spack", "selected: " + ", ".join(tools))
 
     # translate modified paths to cwd_relative if needed
@@ -394,6 +390,15 @@ def run_black(black_cmd, file_list, args):
     return returncode
 
 
+def validate_toolset(arg_value):
+    """Validate --tool and --skip arguments (sets of optionally comma-separated tools)."""
+    tools = set(",".join(arg_value).split(","))  # allow args like 'isort,flake8'
+    for tool in tools:
+        if tool not in tool_names:
+            tty.die("Invaild tool: '%s'" % tool, "Choose from: %s" % ", ".join(tool_names))
+    return tools
+
+
 def style(parser, args):
     # ensure python version is new enough
     if sys.version_info < (3, 6):
@@ -421,26 +426,33 @@ def style(parser, args):
 
         file_list = [prefix_relative(p) for p in file_list]
 
+    # process --tool and --skip arguments
+    selected = set(tool_names)
+    if args.tool is not None:
+        selected = validate_toolset(args.tool)
+    if args.skip is not None:
+        selected -= validate_toolset(args.skip)
+
+    if not selected:
+        tty.msg("Nothing to run.")
+        return
+
     return_code = 0
     with working_dir(args.root):
         if not file_list:
             file_list = changed_files(args.base, args.untracked, args.all)
-        print_style_header(file_list, args)
 
+        print_style_header(file_list, args, selected)
+
+        tools_to_run = [(tool, fn) for tool, fn in tool_order if tool in selected]
         commands = {}
         with spack.bootstrap.ensure_bootstrap_configuration():
-            for tool_name, bootstrap_fn in tool_order:
-                # Skip the tool if it was not requested
-                if not getattr(args, tool_name):
-                    continue
-
+            # bootstrap everything first to get commands
+            for tool_name, bootstrap_fn in tools_to_run:
                 commands[tool_name] = bootstrap_fn()
 
-            for tool_name, bootstrap_fn in tool_order:
-                # Skip the tool if it was not requested
-                if not getattr(args, tool_name):
-                    continue
-
+            # run tools once bootstrapping is done
+            for tool_name, bootstrap_fn in tools_to_run:
                 run_function, required = tools[tool_name]
                 print_tool_header(tool_name)
                 return_code |= run_function(commands[tool_name], file_list, args)
diff --git a/lib/spack/spack/test/cmd/style.py b/lib/spack/spack/test/cmd/style.py
index 35e03b0387..7a5926ae29 100644
--- a/lib/spack/spack/test/cmd/style.py
+++ b/lib/spack/spack/test/cmd/style.py
@@ -224,8 +224,8 @@ def external_style_root(flake8_package_with_errors, tmpdir):
 
 
 @skip_old_python
+@pytest.mark.skipif(not which("isort"), reason="isort is not installed.")
 @pytest.mark.skipif(not which("black"), reason="black is not installed.")
-@pytest.mark.skipif(not which("flake8"), reason="flake8 is not installed.")
 def test_fix_style(external_style_root):
     """Make sure spack style --fix works."""
     tmpdir, py_file = external_style_root
@@ -237,14 +237,9 @@ def test_fix_style(external_style_root):
     shutil.copy(broken_dummy, broken_py)
     assert not filecmp.cmp(broken_py, fixed_py)
 
-    output = style(
-        "--root",
-        str(tmpdir),
-        "--no-mypy",  # mypy doesn't fix, so skip it
-        "--no-flake8",  # flake8 doesn't fix, so skip it
-        "--fix",
-    )
-    print(output)
+    # black and isort are the tools that actually fix things
+    style("--root", str(tmpdir), "--tool", "isort,black", "--fix")
+
     assert filecmp.cmp(broken_py, fixed_py)
 
 
@@ -288,24 +283,19 @@ def test_style(flake8_package, tmpdir):
     with tmpdir.as_cwd():
         relative = os.path.relpath(flake8_package)
 
-        # no args
-        output = style(fail_on_error=False)
-        assert relative in output
-        assert "spack style checks were clean" in output
-
         # one specific arg
-        output = style(flake8_package, fail_on_error=False)
+        output = style("--tool", "flake8", flake8_package, fail_on_error=False)
         assert relative in output
         assert "spack style checks were clean" in output
 
         # specific file that isn't changed
-        output = style(__file__, fail_on_error=False)
+        output = style("--tool", "flake8", __file__, fail_on_error=False)
         assert relative not in output
         assert __file__ in output
         assert "spack style checks were clean" in output
 
     # root-relative paths
-    output = style("--root-relative", flake8_package)
+    output = style("--tool", "flake8", "--root-relative", flake8_package)
     assert root_relative in output
     assert "spack style checks were clean" in output
 
@@ -314,17 +304,25 @@ def test_style(flake8_package, tmpdir):
 @pytest.mark.skipif(not which("flake8"), reason="flake8 is not installed.")
 def test_style_with_errors(flake8_package_with_errors):
     root_relative = os.path.relpath(flake8_package_with_errors, spack.paths.prefix)
-    output = style("--root-relative", flake8_package_with_errors, fail_on_error=False)
+    output = style(
+        "--tool", "flake8", "--root-relative", flake8_package_with_errors, fail_on_error=False
+    )
     assert root_relative in output
     assert style.returncode != 0
     assert "spack style found errors" in output
 
 
 @skip_old_python
-@pytest.mark.skipif(not which("flake8"), reason="flake8 is not installed.")
 @pytest.mark.skipif(not which("black"), reason="black is not installed.")
+@pytest.mark.skipif(not which("flake8"), reason="flake8 is not installed.")
 def test_style_with_black(flake8_package_with_errors):
-    output = style(flake8_package_with_errors, fail_on_error=False)
+    output = style("--tool", "black,flake8", flake8_package_with_errors, fail_on_error=False)
     assert "black found errors" in output
     assert style.returncode != 0
     assert "spack style found errors" in output
+
+
+@skip_old_python
+def test_skip_tools():
+    output = style("--skip", "isort,mypy,black,flake8")
+    assert "Nothing to run" in output
diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index 1b2cfac2de..14d981936d 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -1697,7 +1697,7 @@ _spack_stage() {
 _spack_style() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -b --base -a --all -r --root-relative -U --no-untracked -f --fix --no-isort --no-flake8 --no-mypy --no-black --root"
+        SPACK_COMPREPLY="-h --help -b --base -a --all -r --root-relative -U --no-untracked -f --fix --root -t --tool -s --skip"
     else
         SPACK_COMPREPLY=""
     fi