Fix rustdoc warnings and test cargo doc in CI (#4711)

## Problem

`cargo +nightly doc` is giving a lot of warnings: broken links, naked
URLs, etc.

## Summary of changes

* update the `proc-macro2` dependency so that it can compile on latest
Rust nightly, see dtolnay/proc-macro2#391 and
dtolnay/proc-macro2#398
* allow the `private_intra_doc_links` lint, as linking to something
that's private is always more useful than just mentioning it without a
link: if the link breaks in the future, at least there is a warning due
to that. Also, one might enable
[`--document-private-items`](https://doc.rust-lang.org/cargo/commands/cargo-doc.html#documentation-options)
in the future and make these links work in general.
* fix all the remaining warnings given by `cargo +nightly doc`
* make it possible to run `cargo doc` on stable Rust by updating
`opentelemetry` and associated crates to version 0.19, pulling in a fix
that previously broke `cargo doc` on stable:
open-telemetry/opentelemetry-rust#904
* Add `cargo doc` to CI to ensure that it won't get broken in the
future.

Fixes #2557

## Future work
* Potentially, it might make sense, for development purposes, to publish
the generated rustdocs somewhere, like for example [how the rust
compiler does
it](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/index.html).
I will file an issue for discussion.

Author: arpad-m

.cargo/config.toml

@@ -12,6 +12,11 @@ opt-level = 3
 # Turn on a small amount of optimization in Development mode.
 opt-level = 1
 
+[build]
+# This is only present for local builds, as it will be overridden
+# by the RUSTDOCFLAGS env var in CI.
+rustdocflags = ["-Arustdoc::private_intra_doc_links"]
+
 [alias]
 build_testing = ["build", "--features", "testing"]
 neon = ["run", "--bin", "neon_local"]

.github/workflows/build_and_test.yml

@@ -127,6 +127,11 @@ jobs:
       - name: Run cargo clippy (release)
         run: cargo hack --feature-powerset clippy --release $CLIPPY_COMMON_ARGS
 
+      - name: Check documentation generation
+        run: cargo doc --workspace --no-deps --document-private-items
+        env:
+            RUSTDOCFLAGS: "-Dwarnings -Arustdoc::private_intra_doc_links"
+
       # Use `${{ !cancelled() }}` to run quck tests after the longer clippy run
       - name: Check formatting
         if: ${{ !cancelled() }}

Cargo.lock

@@ -84,9 +84,9 @@ notify = "5.0.0"
 num_cpus = "1.15"
 num-traits = "0.2.15"
 once_cell = "1.13"
-opentelemetry = "0.18.0"
-opentelemetry-otlp = { version = "0.11.0", default_features=false, features = ["http-proto", "trace", "http", "reqwest-client"] }
-opentelemetry-semantic-conventions = "0.10.0"
+opentelemetry = "0.19.0"
+opentelemetry-otlp = { version = "0.12.0", default_features=false, features = ["http-proto", "trace", "http", "reqwest-client"] }
+opentelemetry-semantic-conventions = "0.11.0"
 parking_lot = "0.12"
 pbkdf2 = "0.12.1"
 pin-project-lite = "0.2"
@@ -95,7 +95,7 @@ prost = "0.11"
 rand = "0.8"
 regex = "1.4"
 reqwest = { version = "0.11", default-features = false, features = ["rustls-tls"] }
-reqwest-tracing = { version = "0.4.0", features = ["opentelemetry_0_18"] }
+reqwest-tracing = { version = "0.4.0", features = ["opentelemetry_0_19"] }
 reqwest-middleware = "0.2.0"
 reqwest-retry = "0.2.2"
 routerify = "3"
@@ -130,7 +130,7 @@ toml_edit = "0.19"
 tonic = {version = "0.9", features = ["tls", "tls-roots"]}
 tracing = "0.1"
 tracing-error = "0.2.0"
-tracing-opentelemetry = "0.18.0"
+tracing-opentelemetry = "0.19.0"
 tracing-subscriber = { version = "0.3", default_features = false, features = ["smallvec", "fmt", "tracing-log", "std", "env-filter"] }
 url = "2.2"
 uuid = { version = "1.2", features = ["v4", "serde"] }

Cargo.toml

@@ -19,7 +19,7 @@ const POSTGRES_WAIT_TIMEOUT: Duration = Duration::from_millis(60 * 1000); // mil
 /// Escape a string for including it in a SQL literal. Wrapping the result
 /// with `E'{}'` or `'{}'` is not required, as it returns a ready-to-use
 /// SQL string literal, e.g. `'db'''` or `E'db\\'`.
-/// See https://github.com/postgres/postgres/blob/da98d005cdbcd45af563d0c4ac86d0e9772cd15f/src/backend/utils/adt/quote.c#L47
+/// See <https://github.com/postgres/postgres/blob/da98d005cdbcd45af563d0c4ac86d0e9772cd15f/src/backend/utils/adt/quote.c#L47>
 /// for the original implementation.
 pub fn escape_literal(s: &str) -> String {
     let res = s.replace('\'', "''").replace('\\', "\\\\");

compute_tools/src/pg_helpers.rs

@@ -10,7 +10,7 @@
 //! (non-Neon binaries don't necessarily follow our pidfile conventions).
 //! The pid stored in the file is later used to stop the service.
 //!
-//! See [`lock_file`] module for more info.
+//! See the [`lock_file`](utils::lock_file) module for more info.
 
 use std::ffi::OsStr;
 use std::io::Write;

control_plane/src/background_process.rs

@@ -2,8 +2,9 @@
 //!
 //! In the local test environment, the data for each safekeeper is stored in
 //!
+//! ```text
 //!   .neon/safekeepers/<safekeeper id>
-//!
+//! ```
 use anyhow::Context;
 
 use std::path::PathBuf;

control_plane/src/broker.rs

@@ -2,7 +2,9 @@
 //!
 //! In the local test environment, the data for each endpoint is stored in
 //!
+//! ```text
 //!   .neon/endpoints/<endpoint id>
+//! ```
 //!
 //! Some basic information about the endpoint, like the tenant and timeline IDs,
 //! are stored in the `endpoint.json` file. The `endpoint.json` file is created
@@ -22,7 +24,7 @@
 //!
 //! Directory contents:
 //!
-//! ```ignore
+//! ```text
 //! .neon/endpoints/main/
 //!     compute.log               - log output of `compute_ctl` and `postgres`
 //!     endpoint.json             - serialized `EndpointConf` struct

control_plane/src/endpoint.rs

@@ -2,8 +2,9 @@
 //!
 //! In the local test environment, the data for each safekeeper is stored in
 //!
+//! ```text
 //!   .neon/safekeepers/<safekeeper id>
-//!
+//! ```
 use std::io::Write;
 use std::path::PathBuf;
 use std::process::Child;

control_plane/src/safekeeper.rs

@@ -1,4 +1,4 @@
-//! Helpers for observing duration on HistogramVec / CounterVec / GaugeVec / MetricVec<T>.
+//! Helpers for observing duration on `HistogramVec` / `CounterVec` / `GaugeVec` / `MetricVec<T>`.
 
 use std::{future::Future, time::Instant};