docs: fix the broken intra doc links and check them in CI

Running rustdoc with -D warnings found nine broken links: a misspelt
WGS84, links to methods and constants that are private or in a crate that
is not a dependency, and three redundant explicit targets. Fix each and add
a documentation step to CI so a doc comment cannot drift away from the code
it describes without the build noticing.

.github/workflows/ci.yml

@@ -37,6 +37,12 @@ jobs:
         # meaningful on a quiet machine, but it must still compile so that it
         # does not rot.
         run: cargo build -p apsis-rs --features full --example bench
+      - name: Documentation
+        # Catches a doc link that no longer resolves, which is how a doc
+        # comment drifts away from the code it describes.
+        env:
+          RUSTDOCFLAGS: -D warnings
+        run: cargo doc --workspace --all-features --no-deps
       - name: Check the layer rule
         # README.md states that a crate may only depend on layers to its
         # left. Nothing else in the build enforces that, so a reverse

crates/foundation/apsis-units/src/lib.rs

@@ -3,7 +3,7 @@
 //! Each quantity is a newtype over `f64` that carries its unit in the type
 //! system, so a length cannot be passed where a duration is expected. Units
 //! of the same dimension convert through
-//! [`Quantity::to_unit`](apsis_core::Quantity::to_unit), and each unit also
+//! [`Quantity::to_unit`], and each unit also
 //! offers direct conversions for the common cases.
 //!
 //! A newtype implements both [`Unit`] and [`Quantity`], with its own type as

crates/network/apsis-routing/src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! The topology of a satellite network changes as the satellites move, so a
 //! route is only valid over an interval. This crate computes least cost
-//! routes through a [`Topology`](apsis_topology::Topology) and reports the
+//! routes through a [`Topology`] and reports the
 //! route together with the time it remains valid.
 //!
 //! Two forms of routing are provided:

crates/orbit/apsis-ephemeris/src/lib.rs

@@ -13,7 +13,7 @@
 //!   two-body theory, or read from a file all work the same way.
 //! - [`Sampler`] fills a table by calling a function that produces a state
 //!   from a time. In this workspace that function is normally
-//!   [`apsis_sgp4::Satellite::propagate_at`], but the sampler only requires
+//!   `apsis_sgp4::Satellite::propagate_at`, but the sampler only requires
 //!   a closure, so a test can use an analytic function.
 //!
 //! Interpolation is Hermite cubic, which uses both the position and the

crates/orbit/apsis-ephemeris/src/sampler.rs

@@ -94,7 +94,7 @@ impl Sampler {
     ///
     /// The function maps a time in seconds to a position and velocity. In
     /// this workspace it is normally a closure over
-    /// [`apsis_sgp4::Satellite::propagate_at`], but any function works, so
+    /// `apsis_sgp4::Satellite::propagate_at`, but any function works, so
     /// the sampler can be tested against an analytic orbit.
     ///
     /// Returns an error when the sampler is not usable or when the function

crates/orbit/apsis-kepler/src/anomaly.rs

@@ -78,7 +78,7 @@ pub fn eccentric_from_true(true_anomaly: f64, eccentricity: f64) -> f64 {
 /// by Newton's method. The starting guess is the mean anomaly plus a term
 /// proportional to the eccentricity, which keeps the iteration stable for
 /// eccentricities approaching one. The iteration always terminates, and the
-/// result is the value reached after at most [`MAX_ITERATIONS`] steps.
+/// result is the value reached after at most a fixed number of steps.
 pub fn eccentric_from_mean(mean_anomaly: f64, eccentricity: f64) -> f64 {
     let mean = wrap_to_pi(mean_anomaly);
     // A first order correction to the circular guess.

crates/physics/apsis-frames/src/iau2000/precession.rs

@@ -165,7 +165,7 @@ pub(crate) fn rotation_x(angle: f64) -> Mat3 {
 
 /// Returns a rotation of `angle` about the second axis, in radians.
 ///
-/// The convention is the one of [`rotation_x`].
+/// The sign convention matches the other axis rotations in this module.
 fn rotation_y(angle: f64) -> Mat3 {
     let (sine, cosine) = angle.sin_cos();
     Mat3::from_rows([cosine, 0.0, -sine], [0.0, 1.0, 0.0], [sine, 0.0, cosine])
@@ -173,7 +173,7 @@ fn rotation_y(angle: f64) -> Mat3 {
 
 /// Returns a rotation of `angle` about the third axis, in radians.
 ///
-/// The convention is the one of [`rotation_x`].
+/// The sign convention matches the other axis rotations in this module.
 pub fn rotation_z(angle: f64) -> Mat3 {
     let (sine, cosine) = angle.sin_cos();
     Mat3::from_rows([cosine, sine, 0.0], [-sine, cosine, 0.0], [0.0, 0.0, 1.0])

crates/physics/apsis-geodesy/src/lib.rs

@@ -6,7 +6,7 @@
 //! differ by up to about 0.19 degrees at mid latitudes, so the distinction
 //! matters for pointing and ranging.
 //!
-//! [`Wgs84`] is the ellipsoid used by GPS and by almost all satellite work.
+//! [`WGS84`] is the ellipsoid used by GPS and by almost all satellite work.
 //! Its defining parameters are the semi-major axis and the inverse
 //! flattening; every other quantity is derived from those two, so the
 //! derived values agree with the ones published in the standard to the

crates/rf/apsis-antenna/src/lib.rs

@@ -17,7 +17,7 @@
 //!   uniformly illuminated circular aperture it is about minus 17.6 dB.
 //!
 //! Every function here takes or returns angles in radians and gains as
-//! [`Gain`], so a result can be fed straight into a link budget.
+//! [`apsis_rf::Gain`], so a result can be fed straight into a link budget.
 //!
 //! Sources:
 //!

crates/sim/apsis-sim-engine/src/lib.rs

@@ -13,7 +13,7 @@
 //! implementation meaningful.
 //!
 //! The engine stops for one of four reasons, reported as a
-//! [`StopReason`](crate::StopReason):
+//! [`StopReason`]:
 //! the queue empties, the simulation reaches its time limit, the caller asks
 //! it to stop, or an event limit is reached. The last two exist so that a
 //! model that schedules events forever cannot run without bound.