Rollup merge of #90349 - willcrichton:example-analyzer, r=jyn514

Fix rare ICE during typeck in rustdoc scrape_examples

While testing the `--scrape-examples` extension on the [wasmtime](https://github.com/bytecodealliance/wasmtime) repository, I found some additional edge cases. Specifically, when asking to typecheck a body containing a function call, I would sometimes get an ICE if:
* The body doesn't exist
* The function's HIR node didn't have a type

This adds checks for both of those conditions.

(Also this updates a test to check that the sources of a reverse-dependency are correctly generated and linked.)

r? `@jyn514`

src/librustdoc/scrape_examples.rs

@@ -132,12 +132,28 @@ where
     fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) {
         intravisit::walk_expr(self, ex);
 
-        // Get type of function if expression is a function call
         let tcx = self.tcx;
+
+        // If we visit an item that contains an expression outside a function body,
+        // then we need to exit before calling typeck (which will panic). See
+        // test/run-make/rustdoc-scrape-examples-invalid-expr for an example.
+        let hir = tcx.hir();
+        let owner = hir.local_def_id_to_hir_id(ex.hir_id.owner);
+        if hir.maybe_body_owned_by(owner).is_none() {
+            return;
+        }
+
+        // Get type of function if expression is a function call
         let (ty, span) = match ex.kind {
             hir::ExprKind::Call(f, _) => {
                 let types = tcx.typeck(ex.hir_id.owner);
-                (types.node_type(f.hir_id), ex.span)
+
+                match types.node_type_opt(f.hir_id) {
+                    Some(ty) => (ty, ex.span),
+                    None => {
+                        return;
+                    }
+                }
             }
             hir::ExprKind::MethodCall(_, _, _, span) => {
                 let types = tcx.typeck(ex.hir_id.owner);

src/test/run-make/rustdoc-scrape-examples-invalid-expr/Makefile

@@ -0,0 +1,5 @@
+deps := ex
+
+-include ../rustdoc-scrape-examples-multiple/scrape.mk
+
+all: scrape

src/test/run-make/rustdoc-scrape-examples-invalid-expr/examples/ex.rs

@@ -0,0 +1,2 @@
+pub struct Foo([usize; foobar::f()]);
+fn main() {}

src/test/run-make/rustdoc-scrape-examples-invalid-expr/src/lib.rs

@@ -0,0 +1 @@
+pub const fn f() -> usize { 5 }

src/test/run-make/rustdoc-scrape-examples-multiple/src/lib.rs

@@ -1,4 +1,6 @@
 // @has foobar/fn.ok.html '//*[@class="docblock scraped-example-list"]//*[@class="prev"]' ''
 // @has foobar/fn.ok.html '//*[@class="more-scraped-examples"]' ''
+// @has src/ex/ex.rs.html
+// @has foobar/fn.ok.html '//a[@href="../src/ex/ex.rs.html#2"]' ''
 
 pub fn ok() {}