Module rustc_incremental::assert_dep_graph
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This pass is only used for the UNIT TESTS and DEBUGGING NEEDS
around dependency graph construction. It serves two purposes; it
will dump graphs in graphviz form to disk, and it searches for
#[rustc_if_this_changed] and #[rustc_then_this_would_need]
annotations. These annotations can be used to test whether paths
exist in the graph. These checks run after codegen, so they view the
the final state of the dependency graph. Note that there are
similar assertions found in persist::dirty_clean which check the
initial state of the dependency graph, just after it has been
loaded from disk.
In this code, we report errors on each rustc_if_this_changed
annotation. If a path exists in all cases, then we would report
“all path(s) exist”. Otherwise, we report: “no path to foo” for
each case where no path exists. ui tests can then be
used to check when paths exist or do not.
The full form of the rustc_if_this_changed annotation is
#[rustc_if_this_changed("foo")], which will report a
source node of foo(def_id). The "foo" is optional and
defaults to "Hir" if omitted.
Example:
#[rustc_if_this_changed(Hir)]
fn foo() { }
#[rustc_then_this_would_need(codegen)] //~ ERROR no path from `foo`
fn bar() { }
#[rustc_then_this_would_need(codegen)] //~ ERROR OK
fn baz() { foo(); }