Use envy to parse environment variables for Config

This patch uses the envy crate to parse the environment.  A variable
NITROCLI_KEY can be used to overwrite the configuration for *key*.  This
has the side effect that the NITROCLI_NO_CACHE variable is evaluated as
a boolean variable (instead of only checking whether it is set).  We
also accept two new variables, NITROCLI_MODEL and NITROCLI_VERBOSITY.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/config.rs b/src/config.rs
index 850d217..2e8f3ba 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -26,21 +26,31 @@ use anyhow::Context as _;
 
 /// The configuration for nitrocli, usually read from configuration
 /// files and environment variables.
-#[derive(Clone, Copy, Debug, Default, PartialEq, serde::Deserialize)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, merge::Merge, serde::Deserialize)]
 pub struct Config {
   /// The model to connect to.
   pub model: Option<args::DeviceModel>,
   /// Whether to bypass the cache for all secrets or not.
+  #[merge(strategy = merge::bool::overwrite_false)]
   #[serde(default)]
   pub no_cache: bool,
   /// The log level.
+  #[merge(strategy = merge::num::overwrite_zero)]
   #[serde(default)]
   pub verbosity: u8,
 }
 
 impl Config {
   pub fn load() -> anyhow::Result<Self> {
-    load_user_config().map(|o| o.unwrap_or_default())
+    use merge::Merge as _;
+
+    let mut config = Config::default();
+    if let Some(user_config) = load_user_config()? {
+      config.merge(user_config);
+    }
+    config.merge(load_env_config()?);
+
+    Ok(config)
   }
 
   pub fn update(&mut self, args: &args::Args) {
@@ -62,6 +72,12 @@ fn load_user_config() -> anyhow::Result<Option<Config>> {
   }
 }
 
+fn load_env_config() -> anyhow::Result<Config> {
+  envy::prefixed("NITROCLI_")
+    .from_env()
+    .context("Failed to parse environment variables")
+}
+
 pub fn read_config_file(path: &path::Path) -> anyhow::Result<Config> {
   let s = fs::read_to_string(path)
     .with_context(|| format!("Failed to read configuration file '{}'", path.display()))?;