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| <h1 id="debugging-and-testing-dependencies"><a class="header" href="#debugging-and-testing-dependencies">Debugging and testing dependencies</a></h1> |
| <h2 id="testing-the-dependency-graph"><a class="header" href="#testing-the-dependency-graph">Testing the dependency graph</a></h2> |
| <p>There are various ways to write tests against the dependency graph. The |
| simplest mechanisms are the <code>#[rustc_if_this_changed]</code> and |
| <code>#[rustc_then_this_would_need]</code> annotations. These are used in <a href="tests/ui.html">ui</a> tests to test |
| whether the expected set of paths exist in the dependency graph.</p> |
| <p>As an example, see <a href="https://github.com/rust-lang/rust/blob/master/tests/ui/dep-graph/dep-graph-caller-callee.rs"><code>tests/ui/dep-graph/dep-graph-caller-callee.rs</code></a>, or the |
| tests below.</p> |
| <pre><code class="language-rust ignore">#[rustc_if_this_changed] |
| fn foo() { } |
| |
| #[rustc_then_this_would_need(TypeckTables)] //~ ERROR OK |
| fn bar() { foo(); }</code></pre> |
| <p>This should be read as</p> |
| <blockquote> |
| <p>If this (<code>foo</code>) is changed, then this (i.e. <code>bar</code>)'s TypeckTables would need to be changed.</p> |
| </blockquote> |
| <p>Technically, what occurs is that the test is expected to emit the string "OK" on |
| stderr, associated to this line.</p> |
| <p>You could also add the lines</p> |
| <pre><code class="language-rust ignore">#[rustc_then_this_would_need(TypeckTables)] //~ ERROR no path |
| fn baz() { }</code></pre> |
| <p>Whose meaning is</p> |
| <blockquote> |
| <p>If <code>foo</code> is changed, then <code>baz</code>'s TypeckTables does not need to be changed. |
| The macro must emit an error, and the error message must contains "no path".</p> |
| </blockquote> |
| <p>Recall that the <code>//~ ERROR OK</code> is a comment from the point of view of the Rust |
| code we test, but is meaningful from the point of view of the test itself.</p> |
| <h2 id="debugging-the-dependency-graph"><a class="header" href="#debugging-the-dependency-graph">Debugging the dependency graph</a></h2> |
| <h3 id="dumping-the-graph"><a class="header" href="#dumping-the-graph">Dumping the graph</a></h3> |
| <p>The compiler is also capable of dumping the dependency graph for your |
| debugging pleasure. To do so, pass the <code>-Z dump-dep-graph</code> flag. The |
| graph will be dumped to <code>dep_graph.{txt,dot}</code> in the current |
| directory. You can override the filename with the <code>RUST_DEP_GRAPH</code> |
| environment variable.</p> |
| <p>Frequently, though, the full dep graph is quite overwhelming and not |
| particularly helpful. Therefore, the compiler also allows you to filter |
| the graph. You can filter in three ways:</p> |
| <ol> |
| <li>All edges originating in a particular set of nodes (usually a single node).</li> |
| <li>All edges reaching a particular set of nodes.</li> |
| <li>All edges that lie between given start and end nodes.</li> |
| </ol> |
| <p>To filter, use the <code>RUST_DEP_GRAPH_FILTER</code> environment variable, which should |
| look like one of the following:</p> |
| <pre><code class="language-text">source_filter // nodes originating from source_filter |
| -> target_filter // nodes that can reach target_filter |
| source_filter -> target_filter // nodes in between source_filter and target_filter |
| </code></pre> |
| <p><code>source_filter</code> and <code>target_filter</code> are a <code>&</code>-separated list of strings. |
| A node is considered to match a filter if all of those strings appear in its |
| label. So, for example:</p> |
| <pre><code class="language-text">RUST_DEP_GRAPH_FILTER='-> TypeckTables' |
| </code></pre> |
| <p>would select the predecessors of all <code>TypeckTables</code> nodes. Usually though you |
| want the <code>TypeckTables</code> node for some particular fn, so you might write:</p> |
| <pre><code class="language-text">RUST_DEP_GRAPH_FILTER='-> TypeckTables & bar' |
| </code></pre> |
| <p>This will select only the predecessors of <code>TypeckTables</code> nodes for functions |
| with <code>bar</code> in their name.</p> |
| <p>Perhaps you are finding that when you change <code>foo</code> you need to re-type-check |
| <code>bar</code>, but you don't think you should have to. In that case, you might do:</p> |
| <pre><code class="language-text">RUST_DEP_GRAPH_FILTER='Hir & foo -> TypeckTables & bar' |
| </code></pre> |
| <p>This will dump out all the nodes that lead from <code>Hir(foo)</code> to |
| <code>TypeckTables(bar)</code>, from which you can (hopefully) see the source |
| of the erroneous edge.</p> |
| <h3 id="tracking-down-incorrect-edges"><a class="header" href="#tracking-down-incorrect-edges">Tracking down incorrect edges</a></h3> |
| <p>Sometimes, after you dump the dependency graph, you will find some |
| path that should not exist, but you will not be quite sure how it came |
| to be. <strong>When the compiler is built with debug assertions,</strong> it can |
| help you track that down. Simply set the <code>RUST_FORBID_DEP_GRAPH_EDGE</code> |
| environment variable to a filter. Every edge created in the dep-graph |
| will be tested against that filter – if it matches, a <code>bug!</code> is |
| reported, so you can easily see the backtrace (<code>RUST_BACKTRACE=1</code>).</p> |
| <p>The syntax for these filters is the same as described in the previous |
| section. However, note that this filter is applied to every <strong>edge</strong> |
| and doesn't handle longer paths in the graph, unlike the previous |
| section.</p> |
| <p>Example:</p> |
| <p>You find that there is a path from the <code>Hir</code> of <code>foo</code> to the type |
| check of <code>bar</code> and you don't think there should be. You dump the |
| dep-graph as described in the previous section and open <code>dep-graph.txt</code> |
| to see something like:</p> |
| <pre><code class="language-text">Hir(foo) -> Collect(bar) |
| Collect(bar) -> TypeckTables(bar) |
| </code></pre> |
| <p>That first edge looks suspicious to you. So you set |
| <code>RUST_FORBID_DEP_GRAPH_EDGE</code> to <code>Hir&foo -> Collect&bar</code>, re-run, and |
| then observe the backtrace. Voila, bug fixed!</p> |
| |
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