| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `crates/hir-ty/src/specialization.rs`."><title>specialization.rs - source</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="hir_ty" data-themes="" data-resource-suffix="" data-rustdoc-version="1.92.0 (ded5c06cf 2025-12-08)" data-channel="1.92.0" data-search-js="search-d69d8955.js" data-stringdex-js="stringdex-c3e638e9.js" data-settings-js="settings-c38705f0.js" ><script src="../../static.files/storage-e2aeef58.js"></script><script defer src="../../static.files/src-script-813739b1.js"></script><script defer src="../../src-files.js"></script><script defer src="../../static.files/main-ce535bd0.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-044be391.svg"></head><body class="rustdoc src"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="src-sidebar-title"><h2>Files</h2></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><section id="main-content" class="content"><div class="main-heading"><h1><div class="sub-heading">hir_ty/</div>specialization.rs</h1><rustdoc-toolbar></rustdoc-toolbar></div><div class="example-wrap digits-3"><pre class="rust"><code><a href=#1 id=1 data-nosnippet>1</a><span class="doccomment">//! Impl specialization related things |
| <a href=#2 id=2 data-nosnippet>2</a> |
| <a href=#3 id=3 data-nosnippet>3</a></span><span class="kw">use </span>hir_def::{HasModule, ImplId, nameres::crate_def_map}; |
| <a href=#4 id=4 data-nosnippet>4</a><span class="kw">use </span>intern::sym; |
| <a href=#5 id=5 data-nosnippet>5</a><span class="kw">use </span>rustc_type_ir::inherent::SliceLike; |
| <a href=#6 id=6 data-nosnippet>6</a><span class="kw">use </span>tracing::debug; |
| <a href=#7 id=7 data-nosnippet>7</a> |
| <a href=#8 id=8 data-nosnippet>8</a><span class="kw">use crate</span>::{ |
| <a href=#9 id=9 data-nosnippet>9</a> db::HirDatabase, |
| <a href=#10 id=10 data-nosnippet>10</a> lower::GenericPredicates, |
| <a href=#11 id=11 data-nosnippet>11</a> next_solver::{ |
| <a href=#12 id=12 data-nosnippet>12</a> DbInterner, TypingMode, |
| <a href=#13 id=13 data-nosnippet>13</a> infer::{DbInternerInferExt, traits::ObligationCause}, |
| <a href=#14 id=14 data-nosnippet>14</a> obligation_ctxt::ObligationCtxt, |
| <a href=#15 id=15 data-nosnippet>15</a> util::clauses_as_obligations, |
| <a href=#16 id=16 data-nosnippet>16</a> }, |
| <a href=#17 id=17 data-nosnippet>17</a>}; |
| <a href=#18 id=18 data-nosnippet>18</a> |
| <a href=#19 id=19 data-nosnippet>19</a><span class="comment">// rustc does not have a cycle handling for the `specializes` query, meaning a cycle is a bug, |
| <a href=#20 id=20 data-nosnippet>20</a>// and indeed I was unable to cause cycles even with erroneous code. However, in r-a we can |
| <a href=#21 id=21 data-nosnippet>21</a>// create a cycle if there is an error in the impl's where clauses. I believe well formed code |
| <a href=#22 id=22 data-nosnippet>22</a>// cannot create a cycle, but a cycle handler is required nevertheless. |
| <a href=#23 id=23 data-nosnippet>23</a></span><span class="kw">fn </span>specializes_query_cycle( |
| <a href=#24 id=24 data-nosnippet>24</a> _db: <span class="kw-2">&</span><span class="kw">dyn </span>HirDatabase, |
| <a href=#25 id=25 data-nosnippet>25</a> _specializing_impl_def_id: ImplId, |
| <a href=#26 id=26 data-nosnippet>26</a> _parent_impl_def_id: ImplId, |
| <a href=#27 id=27 data-nosnippet>27</a>) -> bool { |
| <a href=#28 id=28 data-nosnippet>28</a> <span class="bool-val">false |
| <a href=#29 id=29 data-nosnippet>29</a></span>} |
| <a href=#30 id=30 data-nosnippet>30</a> |
| <a href=#31 id=31 data-nosnippet>31</a><span class="doccomment">/// Is `specializing_impl_def_id` a specialization of `parent_impl_def_id`? |
| <a href=#32 id=32 data-nosnippet>32</a>/// |
| <a href=#33 id=33 data-nosnippet>33</a>/// For every type that could apply to `specializing_impl_def_id`, we prove that |
| <a href=#34 id=34 data-nosnippet>34</a>/// the `parent_impl_def_id` also applies (i.e. it has a valid impl header and |
| <a href=#35 id=35 data-nosnippet>35</a>/// its where-clauses hold). |
| <a href=#36 id=36 data-nosnippet>36</a>/// |
| <a href=#37 id=37 data-nosnippet>37</a>/// For the purposes of const traits, we also check that the specializing |
| <a href=#38 id=38 data-nosnippet>38</a>/// impl is not more restrictive than the parent impl. That is, if the |
| <a href=#39 id=39 data-nosnippet>39</a>/// `parent_impl_def_id` is a const impl (conditionally based off of some `[const]` |
| <a href=#40 id=40 data-nosnippet>40</a>/// bounds), then `specializing_impl_def_id` must also be const for the same |
| <a href=#41 id=41 data-nosnippet>41</a>/// set of types. |
| <a href=#42 id=42 data-nosnippet>42</a></span><span class="attr">#[salsa::tracked(cycle_result = specializes_query_cycle)] |
| <a href=#43 id=43 data-nosnippet>43</a></span><span class="kw">fn </span>specializes_query( |
| <a href=#44 id=44 data-nosnippet>44</a> db: <span class="kw-2">&</span><span class="kw">dyn </span>HirDatabase, |
| <a href=#45 id=45 data-nosnippet>45</a> specializing_impl_def_id: ImplId, |
| <a href=#46 id=46 data-nosnippet>46</a> parent_impl_def_id: ImplId, |
| <a href=#47 id=47 data-nosnippet>47</a>) -> bool { |
| <a href=#48 id=48 data-nosnippet>48</a> <span class="kw">let </span>trait_env = db.trait_environment(specializing_impl_def_id.into()); |
| <a href=#49 id=49 data-nosnippet>49</a> <span class="kw">let </span>interner = DbInterner::new_with(db, specializing_impl_def_id.krate(db)); |
| <a href=#50 id=50 data-nosnippet>50</a> |
| <a href=#51 id=51 data-nosnippet>51</a> <span class="kw">let </span>specializing_impl_signature = db.impl_signature(specializing_impl_def_id); |
| <a href=#52 id=52 data-nosnippet>52</a> <span class="kw">let </span>parent_impl_signature = db.impl_signature(parent_impl_def_id); |
| <a href=#53 id=53 data-nosnippet>53</a> |
| <a href=#54 id=54 data-nosnippet>54</a> <span class="comment">// We determine whether there's a subset relationship by: |
| <a href=#55 id=55 data-nosnippet>55</a> // |
| <a href=#56 id=56 data-nosnippet>56</a> // - replacing bound vars with placeholders in impl1, |
| <a href=#57 id=57 data-nosnippet>57</a> // - assuming the where clauses for impl1, |
| <a href=#58 id=58 data-nosnippet>58</a> // - instantiating impl2 with fresh inference variables, |
| <a href=#59 id=59 data-nosnippet>59</a> // - unifying, |
| <a href=#60 id=60 data-nosnippet>60</a> // - attempting to prove the where clauses for impl2 |
| <a href=#61 id=61 data-nosnippet>61</a> // |
| <a href=#62 id=62 data-nosnippet>62</a> // The last three steps are encapsulated in `fulfill_implication`. |
| <a href=#63 id=63 data-nosnippet>63</a> // |
| <a href=#64 id=64 data-nosnippet>64</a> // See RFC 1210 for more details and justification. |
| <a href=#65 id=65 data-nosnippet>65</a> |
| <a href=#66 id=66 data-nosnippet>66</a> // Currently we do not allow e.g., a negative impl to specialize a positive one |
| <a href=#67 id=67 data-nosnippet>67</a> </span><span class="kw">if </span>specializing_impl_signature.is_negative() != parent_impl_signature.is_negative() { |
| <a href=#68 id=68 data-nosnippet>68</a> <span class="kw">return </span><span class="bool-val">false</span>; |
| <a href=#69 id=69 data-nosnippet>69</a> } |
| <a href=#70 id=70 data-nosnippet>70</a> |
| <a href=#71 id=71 data-nosnippet>71</a> <span class="comment">// create a parameter environment corresponding to an identity instantiation of the specializing impl, |
| <a href=#72 id=72 data-nosnippet>72</a> // i.e. the most generic instantiation of the specializing impl. |
| <a href=#73 id=73 data-nosnippet>73</a> </span><span class="kw">let </span>param_env = trait_env; |
| <a href=#74 id=74 data-nosnippet>74</a> |
| <a href=#75 id=75 data-nosnippet>75</a> <span class="comment">// Create an infcx, taking the predicates of the specializing impl as assumptions: |
| <a href=#76 id=76 data-nosnippet>76</a> </span><span class="kw">let </span>infcx = interner.infer_ctxt().build(TypingMode::non_body_analysis()); |
| <a href=#77 id=77 data-nosnippet>77</a> |
| <a href=#78 id=78 data-nosnippet>78</a> <span class="kw">let </span>specializing_impl_trait_ref = |
| <a href=#79 id=79 data-nosnippet>79</a> db.impl_trait(specializing_impl_def_id).unwrap().instantiate_identity(); |
| <a href=#80 id=80 data-nosnippet>80</a> <span class="kw">let </span>cause = <span class="kw-2">&</span>ObligationCause::dummy(); |
| <a href=#81 id=81 data-nosnippet>81</a> <span class="macro">debug!</span>( |
| <a href=#82 id=82 data-nosnippet>82</a> <span class="string">"fulfill_implication({:?}, trait_ref={:?} |- {:?} applies)"</span>, |
| <a href=#83 id=83 data-nosnippet>83</a> param_env, specializing_impl_trait_ref, parent_impl_def_id |
| <a href=#84 id=84 data-nosnippet>84</a> ); |
| <a href=#85 id=85 data-nosnippet>85</a> |
| <a href=#86 id=86 data-nosnippet>86</a> <span class="comment">// Attempt to prove that the parent impl applies, given all of the above. |
| <a href=#87 id=87 data-nosnippet>87</a> |
| <a href=#88 id=88 data-nosnippet>88</a> </span><span class="kw">let </span><span class="kw-2">mut </span>ocx = ObligationCtxt::new(<span class="kw-2">&</span>infcx); |
| <a href=#89 id=89 data-nosnippet>89</a> |
| <a href=#90 id=90 data-nosnippet>90</a> <span class="kw">let </span>parent_args = infcx.fresh_args_for_item(parent_impl_def_id.into()); |
| <a href=#91 id=91 data-nosnippet>91</a> <span class="kw">let </span>parent_impl_trait_ref = db |
| <a href=#92 id=92 data-nosnippet>92</a> .impl_trait(parent_impl_def_id) |
| <a href=#93 id=93 data-nosnippet>93</a> .expect(<span class="string">"expected source impl to be a trait impl"</span>) |
| <a href=#94 id=94 data-nosnippet>94</a> .instantiate(interner, parent_args); |
| <a href=#95 id=95 data-nosnippet>95</a> |
| <a href=#96 id=96 data-nosnippet>96</a> <span class="comment">// do the impls unify? If not, no specialization. |
| <a href=#97 id=97 data-nosnippet>97</a> </span><span class="kw">let </span><span class="prelude-val">Ok</span>(()) = ocx.eq(cause, param_env, specializing_impl_trait_ref, parent_impl_trait_ref) |
| <a href=#98 id=98 data-nosnippet>98</a> <span class="kw">else </span>{ |
| <a href=#99 id=99 data-nosnippet>99</a> <span class="kw">return </span><span class="bool-val">false</span>; |
| <a href=#100 id=100 data-nosnippet>100</a> }; |
| <a href=#101 id=101 data-nosnippet>101</a> |
| <a href=#102 id=102 data-nosnippet>102</a> <span class="comment">// Now check that the source trait ref satisfies all the where clauses of the target impl. |
| <a href=#103 id=103 data-nosnippet>103</a> // This is not just for correctness; we also need this to constrain any params that may |
| <a href=#104 id=104 data-nosnippet>104</a> // only be referenced via projection predicates. |
| <a href=#105 id=105 data-nosnippet>105</a> </span>ocx.register_obligations(clauses_as_obligations( |
| <a href=#106 id=106 data-nosnippet>106</a> GenericPredicates::query_all(db, parent_impl_def_id.into()) |
| <a href=#107 id=107 data-nosnippet>107</a> .iter_instantiated_copied(interner, parent_args.as_slice()), |
| <a href=#108 id=108 data-nosnippet>108</a> cause.clone(), |
| <a href=#109 id=109 data-nosnippet>109</a> param_env, |
| <a href=#110 id=110 data-nosnippet>110</a> )); |
| <a href=#111 id=111 data-nosnippet>111</a> |
| <a href=#112 id=112 data-nosnippet>112</a> <span class="kw">let </span>errors = ocx.evaluate_obligations_error_on_ambiguity(); |
| <a href=#113 id=113 data-nosnippet>113</a> <span class="kw">if </span>!errors.is_empty() { |
| <a href=#114 id=114 data-nosnippet>114</a> <span class="comment">// no dice! |
| <a href=#115 id=115 data-nosnippet>115</a> </span><span class="macro">debug!</span>( |
| <a href=#116 id=116 data-nosnippet>116</a> <span class="string">"fulfill_implication: for impls on {:?} and {:?}, \ |
| <a href=#117 id=117 data-nosnippet>117</a> could not fulfill: {:?} given {:?}"</span>, |
| <a href=#118 id=118 data-nosnippet>118</a> specializing_impl_trait_ref, parent_impl_trait_ref, errors, param_env |
| <a href=#119 id=119 data-nosnippet>119</a> ); |
| <a href=#120 id=120 data-nosnippet>120</a> <span class="kw">return </span><span class="bool-val">false</span>; |
| <a href=#121 id=121 data-nosnippet>121</a> } |
| <a href=#122 id=122 data-nosnippet>122</a> |
| <a href=#123 id=123 data-nosnippet>123</a> <span class="comment">// FIXME: Check impl constness (when we implement const impls). |
| <a href=#124 id=124 data-nosnippet>124</a> |
| <a href=#125 id=125 data-nosnippet>125</a> </span><span class="macro">debug!</span>( |
| <a href=#126 id=126 data-nosnippet>126</a> <span class="string">"fulfill_implication: an impl for {:?} specializes {:?}"</span>, |
| <a href=#127 id=127 data-nosnippet>127</a> specializing_impl_trait_ref, parent_impl_trait_ref |
| <a href=#128 id=128 data-nosnippet>128</a> ); |
| <a href=#129 id=129 data-nosnippet>129</a> |
| <a href=#130 id=130 data-nosnippet>130</a> <span class="bool-val">true |
| <a href=#131 id=131 data-nosnippet>131</a></span>} |
| <a href=#132 id=132 data-nosnippet>132</a> |
| <a href=#133 id=133 data-nosnippet>133</a><span class="comment">// This function is used to avoid creating the query for crates that does not define `#![feature(specialization)]`, |
| <a href=#134 id=134 data-nosnippet>134</a>// as the solver is calling this a lot, and creating the query consumes a lot of memory. |
| <a href=#135 id=135 data-nosnippet>135</a></span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>specializes( |
| <a href=#136 id=136 data-nosnippet>136</a> db: <span class="kw-2">&</span><span class="kw">dyn </span>HirDatabase, |
| <a href=#137 id=137 data-nosnippet>137</a> specializing_impl_def_id: ImplId, |
| <a href=#138 id=138 data-nosnippet>138</a> parent_impl_def_id: ImplId, |
| <a href=#139 id=139 data-nosnippet>139</a>) -> bool { |
| <a href=#140 id=140 data-nosnippet>140</a> <span class="kw">let </span>module = specializing_impl_def_id.loc(db).container; |
| <a href=#141 id=141 data-nosnippet>141</a> |
| <a href=#142 id=142 data-nosnippet>142</a> <span class="comment">// We check that the specializing impl comes from a crate that has specialization enabled. |
| <a href=#143 id=143 data-nosnippet>143</a> // |
| <a href=#144 id=144 data-nosnippet>144</a> // We don't really care if the specialized impl (the parent) is in a crate that has |
| <a href=#145 id=145 data-nosnippet>145</a> // specialization enabled, since it's not being specialized. |
| <a href=#146 id=146 data-nosnippet>146</a> // |
| <a href=#147 id=147 data-nosnippet>147</a> // rustc also checks whether the specializing impls comes from a macro marked |
| <a href=#148 id=148 data-nosnippet>148</a> // `#[allow_internal_unstable(specialization)]`, but `#[allow_internal_unstable]` |
| <a href=#149 id=149 data-nosnippet>149</a> // is an internal feature, std is not using it for specialization nor is likely to |
| <a href=#150 id=150 data-nosnippet>150</a> // ever use it, and we don't have the span information necessary to replicate that. |
| <a href=#151 id=151 data-nosnippet>151</a> </span><span class="kw">let </span>def_map = crate_def_map(db, module.krate(db)); |
| <a href=#152 id=152 data-nosnippet>152</a> <span class="kw">if </span>!def_map.is_unstable_feature_enabled(<span class="kw-2">&</span>sym::specialization) |
| <a href=#153 id=153 data-nosnippet>153</a> && !def_map.is_unstable_feature_enabled(<span class="kw-2">&</span>sym::min_specialization) |
| <a href=#154 id=154 data-nosnippet>154</a> { |
| <a href=#155 id=155 data-nosnippet>155</a> <span class="kw">return </span><span class="bool-val">false</span>; |
| <a href=#156 id=156 data-nosnippet>156</a> } |
| <a href=#157 id=157 data-nosnippet>157</a> |
| <a href=#158 id=158 data-nosnippet>158</a> specializes_query(db, specializing_impl_def_id, parent_impl_def_id) |
| <a href=#159 id=159 data-nosnippet>159</a>}</code></pre></div></section></main></body></html> |
