Use more appropriate return type for `resolve_associated_item`

Previously, the types looked like this:

- None means this is not an associated item (but may be a variant field)
- Some(Err) means this is known to be an error. I think the only way that can happen is if it resolved and but you had your own anchor.
- Some(Ok(_, None)) was impossible.

Now, this returns a nested Option and does the error handling and
fiddling with the side channel in the caller. As a side-effect, it also
removes duplicate error handling.

This has one small change in behavior, which is that
`resolve_primitive_associated_item` now goes through `variant_field` if
it fails to resolve something.  This is not ideal, but since it will be
quickly rejected anyway, I think the performance hit is worth the
cleanup.

This also fixes a bug where struct fields would forget to set the side
channel, adds a test for the bug, and ignores `private_intra_doc_links`
in rustc_resolve (since it's always documented with
--document-private-items).

3 files changed, 33 insertions, 13 deletions

diff --git a/src/test/rustdoc-ui/intra-doc/private.private.stderr b/src/test/rustdoc-ui/intra-doc/private.private.stderr
index cae5b1f20e6..392321f9c60 100644
--- a/src/test/rustdoc-ui/intra-doc/private.private.stderr
+++ b/src/test/rustdoc-ui/intra-doc/private.private.stderr
@@ -1,19 +1,27 @@
 warning: public documentation for `DocMe` links to private item `DontDocMe`
-  --> $DIR/private.rs:5:11
+  --> $DIR/private.rs:7:11
    |
-LL | /// docs [DontDocMe] [DontDocMe::f]
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
    |           ^^^^^^^^^ this item is private
    |
    = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default
    = note: this link resolves only because you passed `--document-private-items`, but will break without
 
 warning: public documentation for `DocMe` links to private item `DontDocMe::f`
-  --> $DIR/private.rs:5:23
+  --> $DIR/private.rs:7:23
    |
-LL | /// docs [DontDocMe] [DontDocMe::f]
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
    |                       ^^^^^^^^^^^^ this item is private
    |
    = note: this link resolves only because you passed `--document-private-items`, but will break without
 
-warning: 2 warnings emitted
+warning: public documentation for `DocMe` links to private item `DontDocMe::x`
+  --> $DIR/private.rs:7:38
+   |
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
+   |                                      ^^^^^^^^^^^^ this item is private
+   |
+   = note: this link resolves only because you passed `--document-private-items`, but will break without
+
+warning: 3 warnings emitted
 
diff --git a/src/test/rustdoc-ui/intra-doc/private.public.stderr b/src/test/rustdoc-ui/intra-doc/private.public.stderr
index 05b202e37fb..5d1c34b9168 100644
--- a/src/test/rustdoc-ui/intra-doc/private.public.stderr
+++ b/src/test/rustdoc-ui/intra-doc/private.public.stderr
@@ -1,19 +1,27 @@
 warning: public documentation for `DocMe` links to private item `DontDocMe`
-  --> $DIR/private.rs:5:11
+  --> $DIR/private.rs:7:11
    |
-LL | /// docs [DontDocMe] [DontDocMe::f]
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
    |           ^^^^^^^^^ this item is private
    |
    = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default
    = note: this link will resolve properly if you pass `--document-private-items`
 
 warning: public documentation for `DocMe` links to private item `DontDocMe::f`
-  --> $DIR/private.rs:5:23
+  --> $DIR/private.rs:7:23
    |
-LL | /// docs [DontDocMe] [DontDocMe::f]
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
    |                       ^^^^^^^^^^^^ this item is private
    |
    = note: this link will resolve properly if you pass `--document-private-items`
 
-warning: 2 warnings emitted
+warning: public documentation for `DocMe` links to private item `DontDocMe::x`
+  --> $DIR/private.rs:7:38
+   |
+LL | /// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
+   |                                      ^^^^^^^^^^^^ this item is private
+   |
+   = note: this link will resolve properly if you pass `--document-private-items`
+
+warning: 3 warnings emitted
 
diff --git a/src/test/rustdoc-ui/intra-doc/private.rs b/src/test/rustdoc-ui/intra-doc/private.rs
index 3782864305f..525332ddaac 100644
--- a/src/test/rustdoc-ui/intra-doc/private.rs
+++ b/src/test/rustdoc-ui/intra-doc/private.rs
@@ -2,12 +2,16 @@
 // revisions: public private
 // [private]compile-flags: --document-private-items
 
-/// docs [DontDocMe] [DontDocMe::f]
+// make sure to update `rustdoc/intra-doc/private.rs` if you update this file
+
+/// docs [DontDocMe] [DontDocMe::f] [DontDocMe::x]
 //~^ WARNING public documentation for `DocMe` links to private item `DontDocMe`
+//~| WARNING public documentation for `DocMe` links to private item `DontDocMe::x`
 //~| WARNING public documentation for `DocMe` links to private item `DontDocMe::f`
-// FIXME: for [private] we should also make sure the link was actually generated
 pub struct DocMe;
-struct DontDocMe;
+struct DontDocMe {
+    x: usize,
+}
 
 impl DontDocMe {
     fn f() {}