jsondoclint: Add option to dump errors as json.

The output looks like:
{
  "errors": [
    {
      "id": "2:2017:1833",
      "kind": {
        "NotFound": [
          [
            {"Field": "index"},
            {"Field": "0:0:1571"},
            {"Field": "links"},
            {"Field": "pointer::read"}
          ]
        ]
      }
    }
  ],
  "path": "/home/nixon/dev/rust/rust/build/x86_64-unknown-linux-gnu/test/rustdoc-json/intra-doc-links/pointer_method/pointer_method.json"
}

4 files changed, 26 insertions, 4 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 0483d50fc2a..bb438f288f2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2115,6 +2115,7 @@ dependencies = [
  "clap 4.0.15",
  "fs-err",
  "rustdoc-json-types",
+ "serde",
  "serde_json",
 ]
 
diff --git a/src/tools/jsondoclint/Cargo.toml b/src/tools/jsondoclint/Cargo.toml
index 0dda3935ed8..8990310a4f4 100644
--- a/src/tools/jsondoclint/Cargo.toml
+++ b/src/tools/jsondoclint/Cargo.toml
@@ -10,4 +10,5 @@ anyhow = "1.0.62"
 clap = { version = "4.0.15", features = ["derive"] }
 fs-err = "2.8.1"
 rustdoc-json-types = { version = "0.1.0", path = "../../rustdoc-json-types" }
+serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.85"
diff --git a/src/tools/jsondoclint/src/json_find.rs b/src/tools/jsondoclint/src/json_find.rs
index 70e7440f730..a183c4068ce 100644
--- a/src/tools/jsondoclint/src/json_find.rs
+++ b/src/tools/jsondoclint/src/json_find.rs
@@ -1,8 +1,9 @@
 use std::fmt::Write;
 
+use serde::Serialize;
 use serde_json::Value;
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
 pub enum SelectorPart {
     Field(String),
     Index(usize),
diff --git a/src/tools/jsondoclint/src/main.rs b/src/tools/jsondoclint/src/main.rs
index 266900ea3a2..05e938f4f7d 100644
--- a/src/tools/jsondoclint/src/main.rs
+++ b/src/tools/jsondoclint/src/main.rs
@@ -1,25 +1,34 @@
+use std::io::{BufWriter, Write};
+
 use anyhow::{bail, Result};
 use clap::Parser;
 use fs_err as fs;
 use rustdoc_json_types::{Crate, Id, FORMAT_VERSION};
+use serde::Serialize;
 use serde_json::Value;
 
 pub(crate) mod item_kind;
 mod json_find;
 mod validator;
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Serialize, Clone)]
 struct Error {
     kind: ErrorKind,
     id: Id,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Serialize, Clone)]
 enum ErrorKind {
     NotFound(Vec<json_find::Selector>),
     Custom(String),
 }
 
+#[derive(Debug, Serialize)]
+struct JsonOutput {
+    path: String,
+    errors: Vec<Error>,
+}
+
 #[derive(Parser)]
 struct Cli {
     /// The path to the json file to be linted
@@ -28,10 +37,13 @@ struct Cli {
     /// Show verbose output
     #[arg(long)]
     verbose: bool,
+
+    #[arg(long)]
+    json_output: Option<String>,
 }
 
 fn main() -> Result<()> {
-    let Cli { path, verbose } = Cli::parse();
+    let Cli { path, verbose, json_output } = Cli::parse();
 
     let contents = fs::read_to_string(&path)?;
     let krate: Crate = serde_json::from_str(&contents)?;
@@ -42,6 +54,13 @@ fn main() -> Result<()> {
     let mut validator = validator::Validator::new(&krate, krate_json);
     validator.check_crate();
 
+    if let Some(json_output) = json_output {
+        let output = JsonOutput { path: path.clone(), errors: validator.errs.clone() };
+        let mut f = BufWriter::new(fs::File::create(json_output)?);
+        serde_json::to_writer(&mut f, &output)?;
+        f.flush()?;
+    }
+
     if !validator.errs.is_empty() {
         for err in validator.errs {
             match err.kind {