From 951c0f8a107446232d9b40d458110250598d14b8 Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@edx.org>
Date: Mon, 9 Oct 2023 14:41:15 -0400
Subject: [PATCH] feat: run commands to get settings

---
 .../20231009_153026_nedbat_command_config.rst |  6 +++
 docs/configuration.rst                        | 14 +++++++
 src/scriv/config.py                           | 10 +++++
 src/scriv/shell.py                            | 19 +++++++++
 tests/test_config.py                          | 40 +++++++++++++++++++
 5 files changed, 89 insertions(+)
 create mode 100644 changelog.d/20231009_153026_nedbat_command_config.rst

diff --git a/changelog.d/20231009_153026_nedbat_command_config.rst b/changelog.d/20231009_153026_nedbat_command_config.rst
new file mode 100644
index 0000000..154a0d2
--- /dev/null
+++ b/changelog.d/20231009_153026_nedbat_command_config.rst
@@ -0,0 +1,6 @@
+Added
+.....
+
+- Settings can now be prefixed with ``command:`` to execute the rest of the
+  setting as a shell command.  The output of the command will be used as the
+  value of the setting.
diff --git a/docs/configuration.rst b/docs/configuration.rst
index 89ede3b..3fcc8dc 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -56,8 +56,13 @@ Settings use the usual syntax, but with some extra features:
 
 - A prefix of ``literal:`` reads a literal data from a source file.
 
+- A prefix of ``command:`` runs the command and uses the output as the setting.
+
 - Value substitutions can make a setting depend on another setting.
 
+These are each explained below:
+
+
 File Prefix
 -----------
 
@@ -159,6 +164,15 @@ When using a Cabal file, the version of the package can be accessed using::
     [scriv]
     version = literal: my-package.cabal: version
 
+Commands
+--------
+
+A ``command:`` prefix indicates that the setting is a shell command to run.
+The output will be used as the setting::
+
+    [scriv]
+    version = command: my_version_tool --next
+
 Value Substitution
 ------------------
 
diff --git a/src/scriv/config.py b/src/scriv/config.py
index e388d8d..0416c56 100644
--- a/src/scriv/config.py
+++ b/src/scriv/config.py
@@ -13,6 +13,7 @@
 from .exceptions import ScrivException
 from .literals import find_literal
 from .optional import tomllib
+from .shell import run_shell_command
 
 logger = logging.getLogger(__name__)
 
@@ -363,6 +364,7 @@ def resolve_value(self, value: str) -> str:
         Prefixes:
             "file:" read the content from a file.
             "literal:" read a literal string from a file.
+            "command:" read the output of a shell command.
 
         """
         value = value.replace("${config:format}", self._options.format)
@@ -392,6 +394,14 @@ def resolve_value(self, value: str) -> str:
                     + f"{value!r}"
                 )
             value = found
+        elif value.startswith("command:"):
+            cmd = value.partition(":")[2].strip()
+            ok, out = run_shell_command(cmd)
+            if not ok:
+                raise ScrivException(f"Command {cmd!r} failed:\n{out}")
+            if out.count("\n") == 1:
+                out = out.rstrip("\r\n")
+            value = out
         return value
 
     def read_file_value(self, file_name: str) -> str:
diff --git a/src/scriv/shell.py b/src/scriv/shell.py
index e2cdc2c..7edd605 100644
--- a/src/scriv/shell.py
+++ b/src/scriv/shell.py
@@ -46,3 +46,22 @@ def run_simple_command(cmd: Union[str, List[str]]) -> str:
     if not ok:
         return ""
     return out.strip()
+
+
+def run_shell_command(cmd: str) -> CmdResult:
+    """
+    Run a command line with a shell.
+    """
+    logger.debug(f"Running shell command {cmd!r}")
+    proc = subprocess.run(
+        cmd,
+        shell=True,
+        check=False,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+    )
+    output = proc.stdout.decode("utf-8")
+    logger.debug(
+        f"Command exited with {proc.returncode} status. Output: {output!r}"
+    )
+    return proc.returncode == 0, output
diff --git a/tests/test_config.py b/tests/test_config.py
index 5fb1fd6..b80fbde 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -344,3 +344,43 @@ def test_no_toml_installed_no_settings(self, temp_dir):
         with without_module(scriv.config, "tomllib"):
             config = Config.read()
         assert config.categories[0] == "Removed"
+
+
+@pytest.mark.parametrize(
+    "cmd_output, result",
+    [
+        ("Xyzzy 2 3\n", "Xyzzy 2 3"),
+        ("Xyzzy 2 3\nAnother line\n", "Xyzzy 2 3\nAnother line\n"),
+    ],
+)
+def test_command_running(mocker, cmd_output, result):
+    # Any setting can be the output of a command.
+    mocker.patch(
+        "scriv.config.run_shell_command", lambda cmd: (True, cmd_output)
+    )
+    text = Config(output_file="command: doesnt-matter").output_file
+    assert text == result
+
+
+def test_real_command_running():
+    text = Config(output_file="command: echo Xyzzy 2 3").output_file
+    assert text == "Xyzzy 2 3"
+
+
+@pytest.mark.parametrize(
+    "bad_cmd, msg_rx",
+    [
+        (
+            "xyzzyplugh",
+            "Couldn't read 'output_file' setting: Command 'xyzzyplugh' failed:",
+        ),
+        (
+            "'hi!2><",
+            "Couldn't read 'output_file' setting: Command \"'hi!2><\" failed:",
+        ),
+    ],
+)
+def test_bad_command(fake_run_command, bad_cmd, msg_rx):
+    # Any setting can be the output of a command.
+    with pytest.raises(ScrivException, match=msg_rx):
+        _ = Config(output_file=f"command: {bad_cmd}").output_file