Rollup merge of #133478 - aDotInTheVoid:finally, r=fmease

jsondocck: Parse, don't validate commands.

Centralizes knowledge of jsondocck syntax into the parser, so the checker doesn't need to know what the indexes are.

[Vaguely related zulip discussion](https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/jsondocck.20rewrite)

I'm very happy this is negative LoC, despite adding a big, documented enum!

r? ``@fmease``

src/tools/jsondocck/src/cache.rs

@@ -28,7 +28,8 @@ impl Cache {
         }
     }
 
-    pub fn value(&self) -> &Value {
-        &self.value
+    // FIXME: Make this failible, so jsonpath syntax error has line number.
+    pub fn select(&self, path: &str) -> Vec<&Value> {
+        jsonpath_lib::select(&self.value, path).unwrap()
     }
 }

src/tools/jsondocck/src/error.rs

@@ -1,29 +1,7 @@
-use std::error::Error;
-use std::fmt;
-
 use crate::Command;
 
 #[derive(Debug)]
-pub enum CkError {
-    /// A check failed. File didn't exist or failed to match the command
-    FailedCheck(String, Command),
-    /// An error triggered by some other error
-    Induced(Box<dyn Error>),
-}
-
-impl fmt::Display for CkError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            CkError::FailedCheck(msg, cmd) => {
-                write!(f, "Failed check: {} on line {}", msg, cmd.lineno)
-            }
-            CkError::Induced(err) => write!(f, "Check failed: {}", err),
-        }
-    }
-}
-
-impl<T: Error + 'static> From<T> for CkError {
-    fn from(err: T) -> CkError {
-        CkError::Induced(Box::new(err))
-    }
+pub struct CkError {
+    pub message: String,
+    pub command: Command,
 }