show env var in error hint

CHANGES.rst

@@ -31,6 +31,8 @@ Unreleased
 -   When generating a command's name from a decorated function's name, the
     suffixes ``_command``, ``_cmd``, ``_group``, and ``_grp`` are removed.
     :issue:`2322`
+-   If ``show_envvar`` then show env var in error messages.
+    :issue:`2695`
 
 
 Version 8.1.7

src/click/core.py

@@ -2372,8 +2372,8 @@ class Option(Parameter):
         For single option boolean flags, the default remains hidden if
         its value is ``False``.
     :param show_envvar: Controls if an environment variable should be
-        shown on the help page. Normally, environment variables are not
-        shown.
+        shown on the help page and error messages.
+        Normally, environment variables are not shown.
     :param prompt: If set to ``True`` or a non empty string then the
         user will be prompted for input. If set to ``True`` the prompt
         will be the option name capitalized.
@@ -2551,6 +2551,12 @@ def to_info_dict(self) -> dict[str, t.Any]:
         )
         return info_dict
 
+    def get_error_hint(self, ctx: Context) -> str:
+        result = super().get_error_hint(ctx)
+        if self.show_envvar:
+            result += f" (env var: '{self.envvar}')"
+        return result
+
     def _parse_decls(
         self, decls: cabc.Sequence[str], expose_value: bool
     ) -> tuple[str | None, list[str], list[str]]:

tests/test_options.py

@@ -527,6 +527,22 @@ def cmd(foo):
     assert "bar" in choices
 
 
+def test_missing_envvar(runner):
+    cli = click.Command(
+        "cli", params=[click.Option(["--foo"], envvar="bar", required=True)]
+    )
+    result = runner.invoke(cli)
+    assert result.exit_code == 2
+    assert "Error: Missing option '--foo'." in result.output
+    cli = click.Command(
+        "cli",
+        params=[click.Option(["--foo"], envvar="bar", show_envvar=True, required=True)],
+    )
+    result = runner.invoke(cli)
+    assert result.exit_code == 2
+    assert "Error: Missing option '--foo' (env var: 'bar')." in result.output
+
+
 def test_case_insensitive_choice(runner):
     @click.command()
     @click.option("--foo", type=click.Choice(["Orange", "Apple"], case_sensitive=False))