Add --print-config option to print the resolved settings at startup.

gunicorn/app/base.py

@@ -191,7 +191,10 @@ class Application(BaseApplication):
         self.chdir()
 
     def run(self):
-        if self.cfg.check_config:
+        if self.cfg.print_config:
+            print(self.cfg)
+
+        if self.cfg.print_config or self.cfg.check_config:
             try:
                 self.load()
             except:

gunicorn/config.py

@@ -51,6 +51,16 @@ class Config(object):
         self.prog = prog or os.path.basename(sys.argv[0])
         self.env_orig = os.environ.copy()
 
+    def __str__(self):
+        lines = []
+        kmax = max(len(k) for k in self.settings)
+        for k in sorted(self.settings):
+            v = self.settings[k].value
+            if callable(v):
+                v = "<%s()>" % v.__qualname__
+            lines.append(f"{k:{kmax}} = {v}")
+        return "\n".join(lines)
+
     def __getattr__(self, name):
         if name not in self.settings:
             raise AttributeError("No configuration setting for: %s" % name)
@@ -936,6 +946,18 @@ class ConfigCheck(Setting):
         """
 
 
+class PrintConfig(Setting):
+    name = "print_config"
+    section = "Debugging"
+    cli = ["--print-config"]
+    validator = validate_bool
+    action = "store_true"
+    default = False
+    desc = """\
+        Print the resolved configuration.
+        """
+
+
 class PreloadApp(Setting):
     name = "preload_app"
     section = "Server Mechanics"

tests/test_config.py

@@ -4,6 +4,7 @@
 # See the NOTICE for more information.
 
 import os
+import re
 import sys
 
 import pytest
@@ -435,3 +436,36 @@ def test_bind_fd():
     with AltArgs(["prog_name", "-b", "fd://42"]):
         app = NoConfigApp()
     assert app.cfg.bind == ["fd://42"]
+
+
+def test_str():
+    c = config.Config()
+    o = str(c)
+
+    # match the first few lines, some different types, but don't go OTT
+    # to avoid needless test fails with changes
+    OUTPUT_MATCH = {
+        'access_log_format': '%(h)s %(l)s %(u)s %(t)s "%(r)s" %(s)s %(b)s "%(f)s" "%(a)s"',
+        'accesslog': 'None',
+        'backlog': '2048',
+        'bind': "['127.0.0.1:8000']",
+        'capture_output': 'False',
+        'child_exit': '<ChildExit.child_exit()>',
+    }
+    for i, line in enumerate(o.splitlines()):
+        m = re.match(r'^(\w+)\s+= ', line)
+        assert m, f"Config line {i} didn't match expected format: {line!r}"
+
+        key = m.group(1)
+        try:
+            s = OUTPUT_MATCH.pop(key)
+        except KeyError:
+            continue
+
+        line_re = fr'^{key}\s+= {re.escape(s)}$'
+        assert re.match(line_re, line), f'{line_re!r} != {line!r}'
+
+        if not OUTPUT_MATCH:
+            break
+    else:
+        assert False, f'missing expected setting lines? {list(OUTPUT_MATCH.keys())}'