unsafety-checking.html - rust-lang/rustc-dev-guide - Git at Google

 <!DOCTYPE HTML>
 <html lang="en" class="light sidebar-visible" dir="ltr">
     <head>
         <!-- Book generated using mdBook -->
         <meta charset="UTF-8">
         <title>Unsafety checking - Rust Compiler Development Guide</title>


         <!-- Custom HTML head -->

         <meta name="description" content="A guide to developing the Rust compiler (rustc)">
         <meta name="viewport" content="width=device-width, initial-scale=1">
         <meta name="theme-color" content="#ffffff">

         <link rel="icon" href="favicon.svg">
         <link rel="shortcut icon" href="favicon.png">
         <link rel="stylesheet" href="css/variables.css">
         <link rel="stylesheet" href="css/general.css">
         <link rel="stylesheet" href="css/chrome.css">
         <link rel="stylesheet" href="css/print.css" media="print">

         <!-- Fonts -->
         <link rel="stylesheet" href="FontAwesome/css/font-awesome.css">
         <link rel="stylesheet" href="fonts/fonts.css">

         <!-- Highlight.js Stylesheets -->
         <link rel="stylesheet" id="highlight-css" href="highlight.css">
         <link rel="stylesheet" id="tomorrow-night-css" href="tomorrow-night.css">
         <link rel="stylesheet" id="ayu-highlight-css" href="ayu-highlight.css">

         <!-- Custom theme stylesheets -->


         <!-- Provide site root and default themes to javascript -->
         <script>
             const path_to_root = "";
             const default_light_theme = "light";
             const default_dark_theme = "navy";
         </script>
         <!-- Start loading toc.js asap -->
         <script src="toc.js"></script>
     </head>
     <body>
     <div id="body-container">
         <!-- Work around some values being stored in localStorage wrapped in quotes -->
         <script>
             try {
                 let theme = localStorage.getItem('mdbook-theme');
                 let sidebar = localStorage.getItem('mdbook-sidebar');

                 if (theme.startsWith('"') && theme.endsWith('"')) {
                     localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
                 }

                 if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
                     localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
                 }
             } catch (e) { }
         </script>

         <!-- Set the theme before any content is loaded, prevents flash -->
         <script>
             const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
             let theme;
             try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
             if (theme === null || theme === undefined) { theme = default_theme; }
             const html = document.documentElement;
             html.classList.remove('light')
             html.classList.add(theme);
             html.classList.add("js");
         </script>

         <input type="checkbox" id="sidebar-toggle-anchor" class="hidden">

         <!-- Hide / unhide sidebar before it is displayed -->
         <script>
             let sidebar = null;
             const sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
             if (document.body.clientWidth >= 1080) {
                 try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
                 sidebar = sidebar || 'visible';
             } else {
                 sidebar = 'hidden';
             }
             sidebar_toggle.checked = sidebar === 'visible';
             html.classList.remove('sidebar-visible');
             html.classList.add("sidebar-" + sidebar);
         </script>

         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
             <!-- populated by js -->
             <mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox>
             <noscript>
                 <iframe class="sidebar-iframe-outer" src="toc.html"></iframe>
             </noscript>
             <div id="sidebar-resize-handle" class="sidebar-resize-handle">
                 <div class="sidebar-resize-indicator"></div>
             </div>
         </nav>

         <div id="page-wrapper" class="page-wrapper">

             <div class="page">
                 <div id="menu-bar-hover-placeholder"></div>
                 <div id="menu-bar" class="menu-bar sticky">
                     <div class="left-buttons">
                         <label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
                             <i class="fa fa-bars"></i>
                         </label>
                         <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
                             <i class="fa fa-paint-brush"></i>
                         </button>
                         <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
                             <li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li>
                             <li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
                             <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
                             <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
                             <li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
                             <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
                         </ul>
                         <button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
                             <i class="fa fa-search"></i>
                         </button>
                     </div>

                     <h1 class="menu-title">Rust Compiler Development Guide</h1>

                     <div class="right-buttons">
                         <a href="print.html" title="Print this book" aria-label="Print this book">
                             <i id="print-button" class="fa fa-print"></i>
                         </a>
                         <a href="https://github.com/rust-lang/rustc-dev-guide" title="Git repository" aria-label="Git repository">
                             <i id="git-repository-button" class="fa fa-github"></i>
                         </a>
                         <a href="https://github.com/rust-lang/rustc-dev-guide/edit/master/src/unsafety-checking.md" title="Suggest an edit" aria-label="Suggest an edit">
                             <i id="git-edit-button" class="fa fa-edit"></i>
                         </a>

                     </div>
                 </div>

                 <div id="search-wrapper" class="hidden">
                     <form id="searchbar-outer" class="searchbar-outer">
                         <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
                     </form>
                     <div id="searchresults-outer" class="searchresults-outer hidden">
                         <div id="searchresults-header" class="searchresults-header"></div>
                         <ul id="searchresults">
                         </ul>
                     </div>
                 </div>

                 <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
                 <script>
                     document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
                     document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
                     Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
                         link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
                     });
                 </script>

                 <div id="content" class="content">
                     <main>
                         <h1 id="unsafety-checking"><a class="header" href="#unsafety-checking">Unsafety checking</a></h1>
 <p>Certain expressions in Rust can violate memory safety and as such need to be
 inside an <code>unsafe</code> block or function. The compiler will also warn if an unsafe
 block is used without any corresponding unsafe operations.</p>
 <h2 id="overview"><a class="header" href="#overview">Overview</a></h2>
 <p>The unsafety check is located in the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_build/check_unsafety/index.html"><code>check_unsafety</code></a> module. It performs a
 walk over the <a href="./thir.html">THIR</a> of a function and all of its closures and inline constants.
 It keeps track of the unsafe context: whether it has entered an <code>unsafe</code> block.
 If an unsafe operation is used outside of an <code>unsafe</code> block, then an error is
 reported. If an unsafe operation is used in an unsafe block then that block is
 marked as used for <a href="#the-unused_unsafe-lint">the unused_unsafe lint</a>.</p>
 <p>The unsafety check needs type information so could potentially be done on the
 HIR, making use of typeck results, THIR or MIR. THIR is chosen because there are
 fewer cases to consider than in HIR, for example unsafe function calls and
 unsafe method calls have the same representation in THIR. The check is not done
 on MIR because safety checks do not depend on control flow so MIR is not
 necessary to use and MIR doesn't have as precise spans for some expressions.</p>
 <p>Most unsafe operations can be identified by checking the <code>ExprKind</code> in THIR and
 checking the type of the argument. For example, dereferences of a raw pointer
 correspond to <code>ExprKind::Deref</code>s with an argument that has a raw pointer type.</p>
 <p>Looking for unsafe Union field accesses is a bit more complex because writing to
 a field of a union is safe. The checker tracks when it's visiting the left-hand
 side of an assignment expression and allows union fields to directly appear
 there, while erroring in all other cases. Union field accesses can also occur
 in patterns, so those have to be walked as well.</p>
 <p>The other complicated safety check is for writes to fields of layout constrained
 structs (such as <a href="https://doc.rust-lang.org/std/ptr/struct.NonNull.html"><code>NonNull</code></a>). These are found by looking for the borrow or
 assignment expression and then visiting the subexpression being borrowed or
 assigned with a separate visitor.</p>
 <h2 id="the-unused_unsafe-lint"><a class="header" href="#the-unused_unsafe-lint">The unused_unsafe lint</a></h2>
 <p>The unused_unsafe lint reports <code>unsafe</code> blocks that can be removed. The unsafety
 checker records whenever it finds an operation that requires unsafe. The lint is
 then reported if either:</p>
 <ul>
 <li>An <code>unsafe</code> block contains no unsafe operations</li>
 <li>An <code>unsafe</code> block is within another unsafe block, and the outer block
 isn't considered unused</li>
 </ul>
 <pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
 </span>#![deny(unused_unsafe)]
 <span class="boring">fn main() {
 </span>let y = 0;
 let x: *const u8 = core::ptr::addr_of!(y);
 unsafe { // lint reported for this block
     unsafe {
         let z = *x;
     }
     let safe_expr = 123;
 }
 unsafe {
     unsafe { // lint reported for this block
         let z = *x;
     }
     let unsafe_expr = *x;
 }
 <span class="boring">}</span></code></pre></pre>
 <h2 id="other-checks-involving-unsafe"><a class="header" href="#other-checks-involving-unsafe">Other checks involving <code>unsafe</code></a></h2>
 <p><a href="https://doc.rust-lang.org/reference/items/traits.html#unsafe-traits">Unsafe traits</a> require an <code>unsafe impl</code> to be implemented, the check for this
 is done as part of <a href="https://github.com/rust-lang/rust/blob/master/compiler/rustc_hir_analysis/src/coherence/unsafety.rs">coherence</a>. The <code>unsafe_code</code> lint is run as a lint pass on
 the ast that searches for unsafe blocks, functions and implementations, as well
 as certain unsafe attributes.</p>

                     </main>

                     <nav class="nav-wrapper" aria-label="Page navigation">
                         <!-- Mobile navigation buttons -->
                             <a rel="prev" href="pat-exhaustive-checking.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                                 <i class="fa fa-angle-left"></i>
                             </a>

                             <a rel="next prefetch" href="mir/dataflow.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
                                 <i class="fa fa-angle-right"></i>
                             </a>

                         <div style="clear: both"></div>
                     </nav>
                 </div>
             </div>

             <nav class="nav-wide-wrapper" aria-label="Page navigation">
                     <a rel="prev" href="pat-exhaustive-checking.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                         <i class="fa fa-angle-left"></i>
                     </a>

                     <a rel="next prefetch" href="mir/dataflow.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
                         <i class="fa fa-angle-right"></i>
                     </a>
             </nav>

         </div>


         <script>
             window.playground_copyable = true;
         </script>


         <script src="elasticlunr.min.js"></script>
         <script src="mark.min.js"></script>
         <script src="searcher.js"></script>

         <script src="clipboard.min.js"></script>
         <script src="highlight.js"></script>
         <script src="book.js"></script>

         <!-- Custom JS scripts -->
         <script src="mermaid.min.js"></script>
         <script src="mermaid-init.js"></script>


     </div>
     </body>
 </html>
	<!DOCTYPE HTML>
	<html lang="en" class="light sidebar-visible" dir="ltr">
	<head>
	<!-- Book generated using mdBook -->
	<meta charset="UTF-8">
	<title>Unsafety checking - Rust Compiler Development Guide</title>


	<!-- Custom HTML head -->

	<meta name="description" content="A guide to developing the Rust compiler (rustc)">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<meta name="theme-color" content="#ffffff">

	<link rel="icon" href="favicon.svg">
	<link rel="shortcut icon" href="favicon.png">
	<link rel="stylesheet" href="css/variables.css">
	<link rel="stylesheet" href="css/general.css">
	<link rel="stylesheet" href="css/chrome.css">
	<link rel="stylesheet" href="css/print.css" media="print">

	<!-- Fonts -->
	<link rel="stylesheet" href="FontAwesome/css/font-awesome.css">
	<link rel="stylesheet" href="fonts/fonts.css">

	<!-- Highlight.js Stylesheets -->
	<link rel="stylesheet" id="highlight-css" href="highlight.css">
	<link rel="stylesheet" id="tomorrow-night-css" href="tomorrow-night.css">
	<link rel="stylesheet" id="ayu-highlight-css" href="ayu-highlight.css">

	<!-- Custom theme stylesheets -->


	<!-- Provide site root and default themes to javascript -->
	<script>
	const path_to_root = "";
	const default_light_theme = "light";
	const default_dark_theme = "navy";
	</script>
	<!-- Start loading toc.js asap -->
	<script src="toc.js"></script>
	</head>
	<body>
	<div id="body-container">
	<!-- Work around some values being stored in localStorage wrapped in quotes -->
	<script>
	try {
	let theme = localStorage.getItem('mdbook-theme');
	let sidebar = localStorage.getItem('mdbook-sidebar');

	if (theme.startsWith('"') && theme.endsWith('"')) {
	localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
	}

	if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
	localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
	}
	} catch (e) { }
	</script>

	<!-- Set the theme before any content is loaded, prevents flash -->
	<script>
	const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
	let theme;
	try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
	if (theme === null \|\| theme === undefined) { theme = default_theme; }
	const html = document.documentElement;
	html.classList.remove('light')
	html.classList.add(theme);
	html.classList.add("js");
	</script>

	<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">

	<!-- Hide / unhide sidebar before it is displayed -->
	<script>
	let sidebar = null;
	const sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
	if (document.body.clientWidth >= 1080) {
	try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
	sidebar = sidebar \|\| 'visible';
	} else {
	sidebar = 'hidden';
	}
	sidebar_toggle.checked = sidebar === 'visible';
	html.classList.remove('sidebar-visible');
	html.classList.add("sidebar-" + sidebar);
	</script>

	<nav id="sidebar" class="sidebar" aria-label="Table of contents">
	<!-- populated by js -->
	<mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox>
	<noscript>
	<iframe class="sidebar-iframe-outer" src="toc.html"></iframe>
	</noscript>
	<div id="sidebar-resize-handle" class="sidebar-resize-handle">
	<div class="sidebar-resize-indicator"></div>
	</div>
	</nav>

	<div id="page-wrapper" class="page-wrapper">

	<div class="page">
	<div id="menu-bar-hover-placeholder"></div>
	<div id="menu-bar" class="menu-bar sticky">
	<div class="left-buttons">
	<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
	<i class="fa fa-bars"></i>
	</label>
	<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
	<i class="fa fa-paint-brush"></i>
	</button>
	<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
	<li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li>
	<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
	<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
	<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
	<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
	<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
	</ul>
	<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
	<i class="fa fa-search"></i>
	</button>
	</div>

	<h1 class="menu-title">Rust Compiler Development Guide</h1>

	<div class="right-buttons">
	<a href="print.html" title="Print this book" aria-label="Print this book">
	<i id="print-button" class="fa fa-print"></i>
	</a>
	<a href="https://github.com/rust-lang/rustc-dev-guide" title="Git repository" aria-label="Git repository">
	<i id="git-repository-button" class="fa fa-github"></i>
	</a>
	<a href="https://github.com/rust-lang/rustc-dev-guide/edit/master/src/unsafety-checking.md" title="Suggest an edit" aria-label="Suggest an edit">
	<i id="git-edit-button" class="fa fa-edit"></i>
	</a>

	</div>
	</div>

	<div id="search-wrapper" class="hidden">
	<form id="searchbar-outer" class="searchbar-outer">
	<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
	</form>
	<div id="searchresults-outer" class="searchresults-outer hidden">
	<div id="searchresults-header" class="searchresults-header"></div>
	<ul id="searchresults">
	</ul>
	</div>
	</div>

	<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
	<script>
	document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
	document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
	Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
	link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
	});
	</script>

	<div id="content" class="content">
	<main>
	<h1 id="unsafety-checking"><a class="header" href="#unsafety-checking">Unsafety checking</a></h1>
	<p>Certain expressions in Rust can violate memory safety and as such need to be
	inside an <code>unsafe</code> block or function. The compiler will also warn if an unsafe
	block is used without any corresponding unsafe operations.</p>
	<h2 id="overview"><a class="header" href="#overview">Overview</a></h2>
	<p>The unsafety check is located in the <a href="https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir_build/check_unsafety/index.html"><code>check_unsafety</code></a> module. It performs a
	walk over the <a href="./thir.html">THIR</a> of a function and all of its closures and inline constants.
	It keeps track of the unsafe context: whether it has entered an <code>unsafe</code> block.
	If an unsafe operation is used outside of an <code>unsafe</code> block, then an error is
	reported. If an unsafe operation is used in an unsafe block then that block is
	marked as used for <a href="#the-unused_unsafe-lint">the unused_unsafe lint</a>.</p>
	<p>The unsafety check needs type information so could potentially be done on the
	HIR, making use of typeck results, THIR or MIR. THIR is chosen because there are
	fewer cases to consider than in HIR, for example unsafe function calls and
	unsafe method calls have the same representation in THIR. The check is not done
	on MIR because safety checks do not depend on control flow so MIR is not
	necessary to use and MIR doesn't have as precise spans for some expressions.</p>
	<p>Most unsafe operations can be identified by checking the <code>ExprKind</code> in THIR and
	checking the type of the argument. For example, dereferences of a raw pointer
	correspond to <code>ExprKind::Deref</code>s with an argument that has a raw pointer type.</p>
	<p>Looking for unsafe Union field accesses is a bit more complex because writing to
	a field of a union is safe. The checker tracks when it's visiting the left-hand
	side of an assignment expression and allows union fields to directly appear
	there, while erroring in all other cases. Union field accesses can also occur
	in patterns, so those have to be walked as well.</p>
	<p>The other complicated safety check is for writes to fields of layout constrained
	structs (such as <a href="https://doc.rust-lang.org/std/ptr/struct.NonNull.html"><code>NonNull</code></a>). These are found by looking for the borrow or
	assignment expression and then visiting the subexpression being borrowed or
	assigned with a separate visitor.</p>
	<h2 id="the-unused_unsafe-lint"><a class="header" href="#the-unused_unsafe-lint">The unused_unsafe lint</a></h2>
	<p>The unused_unsafe lint reports <code>unsafe</code> blocks that can be removed. The unsafety
	checker records whenever it finds an operation that requires unsafe. The lint is
	then reported if either:</p>
	<ul>
	<li>An <code>unsafe</code> block contains no unsafe operations</li>
	<li>An <code>unsafe</code> block is within another unsafe block, and the outer block
	isn't considered unused</li>
	</ul>
	<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
	</span>#![deny(unused_unsafe)]
	<span class="boring">fn main() {
	</span>let y = 0;
	let x: *const u8 = core::ptr::addr_of!(y);
	unsafe { // lint reported for this block
	unsafe {
	let z = *x;
	}
	let safe_expr = 123;
	}
	unsafe {
	unsafe { // lint reported for this block
	let z = *x;
	}
	let unsafe_expr = *x;
	}
	<span class="boring">}</span></code></pre></pre>
	<h2 id="other-checks-involving-unsafe"><a class="header" href="#other-checks-involving-unsafe">Other checks involving <code>unsafe</code></a></h2>
	<p><a href="https://doc.rust-lang.org/reference/items/traits.html#unsafe-traits">Unsafe traits</a> require an <code>unsafe impl</code> to be implemented, the check for this
	is done as part of <a href="https://github.com/rust-lang/rust/blob/master/compiler/rustc_hir_analysis/src/coherence/unsafety.rs">coherence</a>. The <code>unsafe_code</code> lint is run as a lint pass on
	the ast that searches for unsafe blocks, functions and implementations, as well
	as certain unsafe attributes.</p>

	</main>

	<nav class="nav-wrapper" aria-label="Page navigation">
	<!-- Mobile navigation buttons -->
	<a rel="prev" href="pat-exhaustive-checking.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
	<i class="fa fa-angle-left"></i>
	</a>

	<a rel="next prefetch" href="mir/dataflow.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
	<i class="fa fa-angle-right"></i>
	</a>

	<div style="clear: both"></div>
	</nav>
	</div>
	</div>

	<nav class="nav-wide-wrapper" aria-label="Page navigation">
	<a rel="prev" href="pat-exhaustive-checking.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
	<i class="fa fa-angle-left"></i>
	</a>

	<a rel="next prefetch" href="mir/dataflow.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
	<i class="fa fa-angle-right"></i>
	</a>
	</nav>

	</div>




	<script>
	window.playground_copyable = true;
	</script>


	<script src="elasticlunr.min.js"></script>
	<script src="mark.min.js"></script>
	<script src="searcher.js"></script>

	<script src="clipboard.min.js"></script>
	<script src="highlight.js"></script>
	<script src="book.js"></script>

	<!-- Custom JS scripts -->
	<script src="mermaid.min.js"></script>
	<script src="mermaid-init.js"></script>


	</div>
	</body>
	</html>