Turbopack: chore: Remove dead experimental.ppr struct field (#85792)

- `experimental.ppr` was replaced with `cacheComponents`.
- It's still in the zod and TS type schemas, I think for our error messages on the Next.js side, but Turbopack only needs to know about the fields that Turbopack cares about. Serde silently ignores unknown fields by default.
- Nothing was reading this field from this struct.
- This unit test coverage is very overkill.

Author: bgw

crates/next-core/src/next_config.rs

@@ -863,9 +863,6 @@ pub struct ExperimentalConfig {
     /// Automatically apply the "modularize_imports" optimization to imports of
     /// the specified packages.
     optimize_package_imports: Option<Vec<RcStr>>,
-    /// Using this feature will enable the `react@experimental` for the `app`
-    /// directory.
-    ppr: Option<ExperimentalPartialPrerendering>,
     taint: Option<bool>,
     proxy_timeout: Option<f64>,
     /// enables the minification of server code.
@@ -962,53 +959,6 @@ fn test_cache_life_profiles_invalid() {
     );
 }
 
-#[derive(
-    Clone, Debug, PartialEq, Serialize, Deserialize, TraceRawVcs, NonLocalValue, OperationValue,
-)]
-#[serde(rename_all = "lowercase")]
-pub enum ExperimentalPartialPrerenderingIncrementalValue {
-    Incremental,
-}
-
-#[derive(
-    Clone, Debug, PartialEq, Deserialize, Serialize, TraceRawVcs, NonLocalValue, OperationValue,
-)]
-#[serde(untagged)]
-pub enum ExperimentalPartialPrerendering {
-    Boolean(bool),
-    Incremental(ExperimentalPartialPrerenderingIncrementalValue),
-}
-
-#[test]
-fn test_parse_experimental_partial_prerendering() {
-    let json = serde_json::json!({
-        "ppr": "incremental"
-    });
-    let config: ExperimentalConfig = serde_json::from_value(json).unwrap();
-    assert_eq!(
-        config.ppr,
-        Some(ExperimentalPartialPrerendering::Incremental(
-            ExperimentalPartialPrerenderingIncrementalValue::Incremental
-        ))
-    );
-
-    let json = serde_json::json!({
-        "ppr": true
-    });
-    let config: ExperimentalConfig = serde_json::from_value(json).unwrap();
-    assert_eq!(
-        config.ppr,
-        Some(ExperimentalPartialPrerendering::Boolean(true))
-    );
-
-    // Expect if we provide a random string, it will fail.
-    let json = serde_json::json!({
-        "ppr": "random"
-    });
-    let config = serde_json::from_value::<ExperimentalConfig>(json);
-    assert!(config.is_err());
-}
-
 #[derive(
     Clone, Debug, PartialEq, Eq, Serialize, Deserialize, TraceRawVcs, NonLocalValue, OperationValue,
 )]
@@ -1719,22 +1669,6 @@ impl NextConfig {
         }
     }
 
-    #[turbo_tasks::function]
-    pub fn enable_ppr(&self) -> Vc<bool> {
-        Vc::cell(
-            self.experimental
-                .ppr
-                .as_ref()
-                .map(|ppr| match ppr {
-                    ExperimentalPartialPrerendering::Incremental(
-                        ExperimentalPartialPrerenderingIncrementalValue::Incremental,
-                    ) => true,
-                    ExperimentalPartialPrerendering::Boolean(b) => *b,
-                })
-                .unwrap_or(false),
-        )
-    }
-
     #[turbo_tasks::function]
     pub fn enable_taint(&self) -> Vc<bool> {
         Vc::cell(self.experimental.taint.unwrap_or(false))