feat: add ZIZMOR_CONFIG (#789)

Author: woodruffw

docs/release-notes.md

@@ -22,6 +22,11 @@ of `zizmor`.
   will redirect to the new one, but users should update any old
   links to limit confusion
 
+### New Features 🌈
+
+* `zizmor` now supports the `ZIZMOR_CONFIG` environment variable as an
+  alternative to `--config` (#789)
+
 ## v1.7.0
 
 This release comes with **four** new audits: [obfuscation], [stale-action-refs],

docs/snippets/help.txt

@@ -29,7 +29,7 @@ Options:
       --color <MODE>
           Control the use of color in output [possible values: auto, always, never]
   -c, --config <CONFIG>
-          The configuration file to load. By default, any config will be discovered relative to $CWD
+          The configuration file to load. By default, any config will be discovered relative to $CWD [env: ZIZMOR_CONFIG=]
       --no-config
           Disable all configuration loading
       --no-exit-codes

docs/usage.md

@@ -502,6 +502,14 @@ the `--config` argument. With `--config`, the file can be named anything:
 zizmor --config my-zizmor-config.yml /dir/to/audit
 ```
 
+!!! tip
+
+    Starting with `v1.8.0`, you can use the `ZIZMOR_CONFIG` environment
+    variable to specify a configuration file.
+
+    `ZIZMOR_CONFIG=my-config.yml` is equivalent to
+    `--config my-config.yml`.
+
 [will discover it]: ./configuration.md#precedence
 
 See [Configuration: `rules.<id>.ignore`](./configuration.md#rulesidignore) for

src/main.rs

@@ -89,7 +89,7 @@ struct App {
 
     /// The configuration file to load. By default, any config will be
     /// discovered relative to $CWD.
-    #[arg(short, long, group = "conf")]
+    #[arg(short, long, env = "ZIZMOR_CONFIG", group = "conf")]
     config: Option<Utf8PathBuf>,
 
     /// Disable all configuration loading.