bug(config): Fix handling of the default value for `ProxyConfig::enab…

…led` (#19604)

Because the `enabled` field has a serde field-level default of `true` but a
type-level default of `false`, this struct will not survive
serialize-deserialize pairs intact. This change fixes the field default check
and adds a partial proptest for the back-and-forth conversion of the whole
struct.

lib/vector-core/Cargo.toml

@@ -89,6 +89,7 @@ ndarray-stats = "0.5.1"
 noisy_float = "0.2.0"
 rand = "0.8.5"
 rand_distr = "0.4.3"
+serde_yaml = { version = "0.9.30", default-features = false }
 tracing-subscriber = { version = "0.3.18", default-features = false, features = ["env-filter", "fmt", "ansi", "registry"] }
 vector-common = { path = "../vector-common", default-features = false, features = ["test"] }
 

lib/vector-core/src/config/proxy.rs

@@ -54,7 +54,7 @@ pub struct ProxyConfig {
     /// Enables proxying support.
     #[serde(
         default = "ProxyConfig::default_enabled",
-        skip_serializing_if = "is_default"
+        skip_serializing_if = "is_enabled"
     )]
     pub enabled: bool,
 
@@ -105,6 +105,11 @@ impl Default for ProxyConfig {
     }
 }
 
+#[allow(clippy::trivially_copy_pass_by_ref)] // Calling convention is required by serde
+fn is_enabled(e: &bool) -> bool {
+    e == &true
+}
+
 impl ProxyConfig {
     fn default_enabled() -> bool {
         true
@@ -204,11 +209,44 @@ mod tests {
         header::{AUTHORIZATION, PROXY_AUTHORIZATION},
         HeaderName, HeaderValue, Uri,
     };
+    use proptest::prelude::*;
 
     const PROXY_HEADERS: [HeaderName; 2] = [AUTHORIZATION, PROXY_AUTHORIZATION];
 
     use super::*;
 
+    impl Arbitrary for ProxyConfig {
+        type Parameters = ();
+        type Strategy = BoxedStrategy<Self>;
+
+        fn arbitrary_with((): Self::Parameters) -> Self::Strategy {
+            (
+                any::<bool>(),
+                any::<Option<String>>(),
+                any::<Option<String>>(),
+            )
+                .prop_map(|(enabled, http, https)| Self {
+                    enabled,
+                    http,
+                    https,
+                    // TODO: Neither NoProxy nor IpCidr contained with in it supports proptest. Once
+                    // they support proptest, add another any here.
+                    no_proxy: Default::default(),
+                })
+                .boxed()
+        }
+    }
+
+    proptest! {
+        #[test]
+        fn encodes_and_decodes_through_yaml(config:ProxyConfig) {
+            let yaml = serde_yaml::to_string(&config).expect("Could not serialize config");
+            let reloaded: ProxyConfig = serde_yaml::from_str(&yaml)
+                .expect("Could not deserialize config");
+            assert_eq!(config, reloaded);
+        }
+    }
+
     #[test]
     fn merge_simple() {
         let first = ProxyConfig::default();