Fix show_envvar output for a sequence or an empty envvar

CHANGES.md

@@ -24,6 +24,11 @@ Unreleased
 - A command's short help no longer stops at an abbreviation such as `vs.` or `e.g.`
   inside the first sentence. A period ends the sentence only when it closes the text
   or the next word does not start in lowercase. {pr}`3865`
+- With `show_envvar=True`, an option's error message now prints all variables of an
+  `envvar` sequence instead of the `repr` of the sequence. {pr}`3884`
+- An empty `envvar`, such as `[]` or `""`, shows the same help and error message as
+  no `envvar` when `show_envvar=True`. The help screen used to show `[env var: ]`.
+  {pr}`3884`
 
 ## Version 8.5.0
 

src/click/core.py

@@ -3270,8 +3270,12 @@ def get_default(
 
     def get_error_hint(self, ctx: Context | None) -> str:
         result = super().get_error_hint(ctx)
-        if self.show_envvar and self.envvar is not None:
-            result += f" (env var: '{self.envvar}')"
+        if self.show_envvar and self.envvar:
+            envvars = [self.envvar] if isinstance(self.envvar, str) else self.envvar
+            # An environment variable is allowed to feature a space or a comma on all
+            # platforms, hence the quotes around each.
+            var_str = ", ".join(f"'{var}'" for var in envvars)
+            result += f" (env var: {var_str})"
         return result
 
     def _parse_decls(
@@ -3439,15 +3443,14 @@ def get_help_extra(self, ctx: Context) -> types.OptionHelpExtra:
         if self.show_envvar:
             envvar = self.envvar
 
-            if envvar is None:
-                if (
-                    self.allow_from_autoenv
-                    and ctx.auto_envvar_prefix is not None
-                    and self.name
-                ):
-                    envvar = f"{ctx.auto_envvar_prefix}_{self.name.upper()}"
+            if not envvar and (
+                self.allow_from_autoenv
+                and ctx.auto_envvar_prefix is not None
+                and self.name
+            ):
+                envvar = f"{ctx.auto_envvar_prefix}_{self.name.upper()}"
 
-            if envvar is not None:
+            if envvar:
                 if isinstance(envvar, str):
                     extra["envvars"] = (envvar,)
                 else:

tests/test_options.py

@@ -875,6 +875,23 @@ def foo_bar(baz):
     assert "TEST_FOO_BAR_BAZ" in result.output
 
 
+@pytest.mark.parametrize("envvar", [None, [], ""])
+@pytest.mark.parametrize(
+    ("auto_envvar_prefix", "expected"),
+    [
+        (None, "  --units TEXT\n"),
+        ("WEATHER", "  --units TEXT  [env var: WEATHER_UNITS]\n"),
+    ],
+)
+def test_show_envvar_empty(runner, envvar, auto_envvar_prefix, expected):
+    """An empty ``envvar`` shows the same help as no ``envvar``."""
+    option = click.Option(["--units"], envvar=envvar, show_envvar=True)
+    cli = click.Command("cli", params=[option])
+    result = runner.invoke(cli, ["--help"], auto_envvar_prefix=auto_envvar_prefix)
+    assert not result.exception
+    assert expected in result.output
+
+
 def test_custom_validation(runner):
     def validate_pos_int(ctx, param, value):
         if value < 0:
@@ -1018,6 +1035,25 @@ def test_missing_envvar(runner):
     assert "Error: Missing option '--foo'." in result.output
 
 
+@pytest.mark.parametrize(
+    ("envvar", "expected"),
+    [
+        ("UNITS", "'--units' (env var: 'UNITS')"),
+        (["UNITS"], "'--units' (env var: 'UNITS')"),
+        (["WEATHER_UNITS", "UNITS"], "'--units' (env var: 'WEATHER_UNITS', 'UNITS')"),
+        (("WEATHER_UNITS", "UNITS"), "'--units' (env var: 'WEATHER_UNITS', 'UNITS')"),
+        ([], "'--units'"),
+        ("", "'--units'"),
+    ],
+)
+def test_missing_envvar_sequence(runner, envvar, expected):
+    """The error hint names each variable of a sequence ``envvar``."""
+    option = click.Option(["--units"], envvar=envvar, show_envvar=True, required=True)
+    result = runner.invoke(click.Command("cli", params=[option]))
+    assert result.exit_code == 2
+    assert f"Error: Missing option {expected}." in result.output
+
+
 def test_case_insensitive_choice(runner):
     @click.command()
     @click.option("--foo", type=click.Choice(["Orange", "Apple"], case_sensitive=False))