Add CI check to ensure that rustdoc JSON FORMAT_VERSION is correctly updated

src/build_helper/src/git.rs

@@ -198,7 +198,7 @@ fn get_latest_upstream_commit_that_modified_files(
 /// author.
 ///
 /// If we are in CI, we simply return our first parent.
-fn get_closest_upstream_commit(
+pub fn get_closest_upstream_commit(
     git_dir: Option<&Path>,
     config: &GitConfig<'_>,
     env: CiEnv,

src/tools/tidy/src/lib.rs

@@ -83,6 +83,7 @@ pub mod pal;
 pub mod rustdoc_css_themes;
 pub mod rustdoc_gui_tests;
 pub mod rustdoc_js;
+pub mod rustdoc_json;
 pub mod rustdoc_templates;
 pub mod style;
 pub mod target_policy;

src/tools/tidy/src/main.rs

@@ -110,6 +110,7 @@ fn main() {
         check!(rustdoc_css_themes, &librustdoc_path);
         check!(rustdoc_templates, &librustdoc_path);
         check!(rustdoc_js, &librustdoc_path, &tools_path, &src_path);
+        check!(rustdoc_json, &src_path);
         check!(known_bug, &crashes_path);
         check!(unknown_revision, &tests_path);
 

src/tools/tidy/src/rustdoc_json.rs

@@ -0,0 +1,91 @@
+//! Tidy check to ensure that `FORMAT_VERSION` was correctly updated if `rustdoc-json-types` was
+//! updated as well.
+
+use std::ffi::OsStr;
+use std::path::Path;
+use std::process::Command;
+
+use build_helper::ci::CiEnv;
+use build_helper::git::{GitConfig, get_closest_upstream_commit};
+use build_helper::stage0_parser::parse_stage0_file;
+
+fn git_diff<S: AsRef<OsStr>>(base_commit: &str, extra_arg: S) -> Option<String> {
+    let output = Command::new("git").arg("diff").arg(base_commit).arg(extra_arg).output().ok()?;
+    Some(String::from_utf8_lossy(&output.stdout).into())
+}
+
+pub fn check(src_path: &Path, bad: &mut bool) {
+    println!("Checking tidy rustdoc_json...");
+    let stage0 = parse_stage0_file();
+    let base_commit = match get_closest_upstream_commit(
+        None,
+        &GitConfig {
+            nightly_branch: &stage0.config.nightly_branch,
+            git_merge_commit_email: &stage0.config.git_merge_commit_email,
+        },
+        CiEnv::current(),
+    ) {
+        Ok(Some(commit)) => commit,
+        Ok(None) => {
+            *bad = true;
+            eprintln!("error: no base commit found for rustdoc_json check");
+            return;
+        }
+        Err(error) => {
+            *bad = true;
+            eprintln!(
+                "error: failed to retrieve base commit for rustdoc_json check because of `{error}`"
+            );
+            return;
+        }
+    };
+
+    // First we check that `src/rustdoc-json-types` was modified.
+    match git_diff(&base_commit, "--name-status") {
+        Some(output) => {
+            if !output
+                .lines()
+                .any(|line| line.starts_with("M") && line.contains("src/rustdoc-json-types"))
+            {
+                // `rustdoc-json-types` was not modified so nothing more to check here.
+                println!("`rustdoc-json-types` was not modified.");
+                return;
+            }
+        }
+        None => {
+            *bad = true;
+            eprintln!("error: failed to run `git diff` in rustdoc_json check");
+            return;
+        }
+    }
+    // Then we check that if `FORMAT_VERSION` was updated, the `Latest feature:` was also updated.
+    match git_diff(&base_commit, src_path.join("rustdoc-json-types")) {
+        Some(output) => {
+            let mut format_version_updated = false;
+            let mut latest_feature_comment_updated = false;
+            for line in output.lines() {
+                if line.starts_with("+pub const FORMAT_VERSION: u32 =") {
+                    format_version_updated = true;
+                } else if line.starts_with("+// Latest feature:") {
+                    latest_feature_comment_updated = true;
+                }
+            }
+            if format_version_updated != latest_feature_comment_updated {
+                *bad = true;
+                if latest_feature_comment_updated {
+                    eprintln!(
+                        "error: `Latest feature` comment was updated whereas `FORMAT_VERSION` wasn't"
+                    );
+                } else {
+                    eprintln!(
+                        "error: `Latest feature` comment was not updated whereas `FORMAT_VERSION` was"
+                    );
+                }
+            }
+        }
+        None => {
+            *bad = true;
+            eprintln!("error: failed to run `git diff` in rustdoc_json check");
+        }
+    }
+}