Merge #6472

6472: Add `static` modifier for associated functions r=matklad a=p3achyjr

Adds static semantic token modifier to associated functions, resolves #6194 

## Info

- Associated functions are more-or-less equivalent to static methods in other languages. This PR checks, for each function, whether that function has a self_param, and whether it's enclosed in a trait/impl.

## Changes

- Added method ```is_associated``` to code_model::Function. This basically gets the source from the ast, and checks whether the enclosing scope is an impl or trait.
- Added `static` to HighlightModifiers
- Added unit test

## Tests

- Ran ```cargo test```

Co-authored-by: Anatol Liu <[email protected]>

6 files changed, 94 insertions, 3 deletions

diff --git a/crates/ide/src/syntax_highlighting.rs b/crates/ide/src/syntax_highlighting.rs
index 37ab7a8f6..1ed77b40b 100644
--- a/crates/ide/src/syntax_highlighting.rs
+++ b/crates/ide/src/syntax_highlighting.rs
@@ -6,7 +6,7 @@ pub(crate) mod tags;
 #[cfg(test)]
 mod tests;
 
-use hir::{Local, Name, Semantics, VariantDef};
+use hir::{AsAssocItem, Local, Name, Semantics, VariantDef};
 use ide_db::{
     defs::{Definition, NameClass, NameRefClass},
     RootDatabase,
@@ -746,6 +746,9 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
                 if func.is_unsafe(db) {
                     h |= HighlightModifier::Unsafe;
                 }
+                if func.as_assoc_item(db).is_some() && func.self_param(db).is_none() {
+                    h |= HighlightModifier::Static;
+                }
                 return h;
             }
             hir::ModuleDef::Adt(hir::Adt::Struct(_)) => HighlightTag::Struct,
diff --git a/crates/ide/src/syntax_highlighting/tags.rs b/crates/ide/src/syntax_highlighting/tags.rs
index e8f78ad52..65e0671a5 100644
--- a/crates/ide/src/syntax_highlighting/tags.rs
+++ b/crates/ide/src/syntax_highlighting/tags.rs
@@ -65,6 +65,8 @@ pub enum HighlightModifier {
     Consuming,
     Unsafe,
     Callable,
+    /// Used for associated functions
+    Static,
 }
 
 impl HighlightTag {
@@ -124,6 +126,7 @@ impl HighlightModifier {
         HighlightModifier::Consuming,
         HighlightModifier::Unsafe,
         HighlightModifier::Callable,
+        HighlightModifier::Static,
     ];
 
     fn as_str(self) -> &'static str {
@@ -137,6 +140,7 @@ impl HighlightModifier {
             HighlightModifier::Consuming => "consuming",
             HighlightModifier::Unsafe => "unsafe",
             HighlightModifier::Callable => "callable",
+            HighlightModifier::Static => "static",
         }
     }
 
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlight_assoc_functions.html b/crates/ide/src/syntax_highlighting/test_data/highlight_assoc_functions.html
new file mode 100644
index 000000000..cd80d72b7
--- /dev/null
+++ b/crates/ide/src/syntax_highlighting/test_data/highlight_assoc_functions.html
@@ -0,0 +1,56 @@
+
+<style>
+body                { margin: 0; }
+pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padding: 0.4em; }
+
+.lifetime           { color: #DFAF8F; font-style: italic; }
+.comment            { color: #7F9F7F; }
+.documentation      { color: #629755; }
+.injected           { opacity: 0.65 ; }
+.struct, .enum      { color: #7CB8BB; }
+.enum_variant       { color: #BDE0F3; }
+.string_literal     { color: #CC9393; }
+.field              { color: #94BFF3; }
+.function           { color: #93E0E3; }
+.function.unsafe    { color: #BC8383; }
+.operator.unsafe    { color: #BC8383; }
+.parameter          { color: #94BFF3; }
+.text               { color: #DCDCCC; }
+.type               { color: #7CB8BB; }
+.builtin_type       { color: #8CD0D3; }
+.type_param         { color: #DFAF8F; }
+.attribute          { color: #94BFF3; }
+.numeric_literal    { color: #BFEBBF; }
+.bool_literal       { color: #BFE6EB; }
+.macro              { color: #94BFF3; }
+.module             { color: #AFD8AF; }
+.value_param        { color: #DCDCCC; }
+.variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
+.mutable            { text-decoration: underline; }
+.escape_sequence    { color: #94BFF3; }
+.keyword            { color: #F0DFAF; font-weight: bold; }
+.keyword.unsafe     { color: #BC8383; font-weight: bold; }
+.control            { font-style: italic; }
+
+.unresolved_reference { color: #FC5555; text-decoration: wavy underline; }
+</style>
+<pre><code><span class="keyword">fn</span> <span class="function declaration">not_static</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+
+<span class="keyword">struct</span> <span class="struct declaration">foo</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+
+<span class="keyword">impl</span> <span class="struct">foo</span> <span class="punctuation">{</span>
+    <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration static">is_static</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+    <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration">is_not_static</span><span class="punctuation">(</span><span class="operator">&</span><span class="self_keyword">self</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+<span class="punctuation">}</span>
+
+<span class="keyword">trait</span> <span class="trait declaration">t</span> <span class="punctuation">{</span>
+    <span class="keyword">fn</span> <span class="function declaration static">t_is_static</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+    <span class="keyword">fn</span> <span class="function declaration">t_is_not_static</span><span class="punctuation">(</span><span class="operator">&</span><span class="self_keyword">self</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+<span class="punctuation">}</span>
+
+<span class="keyword">impl</span> <span class="trait">t</span> <span class="keyword">for</span> <span class="struct">foo</span> <span class="punctuation">{</span>
+    <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration static">is_static</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+    <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration">is_not_static</span><span class="punctuation">(</span><span class="operator">&</span><span class="self_keyword">self</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+<span class="punctuation">}</span>
+        </code></pre>
\ No newline at end of file
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlight_doctest.html b/crates/ide/src/syntax_highlighting/test_data/highlight_doctest.html
index f44fe457d..6be88f856 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlight_doctest.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlight_doctest.html
@@ -53,7 +53,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="comment documentation">/// #</span><span class="generic injected"> </span><span class="attribute injected">#</span><span class="attribute injected">!</span><span class="attribute injected">[</span><span class="function attribute injected">allow</span><span class="punctuation injected">(</span><span class="attribute injected">unused_mut</span><span class="punctuation injected">)</span><span class="attribute injected">]</span>
     <span class="comment documentation">/// </span><span class="keyword injected">let</span><span class="generic injected"> </span><span class="keyword injected">mut</span><span class="generic injected"> </span><span class="variable declaration injected mutable">foo</span><span class="punctuation injected">:</span><span class="generic injected"> </span><span class="struct injected">Foo</span><span class="generic injected"> </span><span class="operator injected">=</span><span class="generic injected"> </span><span class="struct injected">Foo</span><span class="operator injected">::</span><span class="function injected">new</span><span class="punctuation injected">(</span><span class="punctuation injected">)</span><span class="punctuation injected">;</span><span class="punctuation injected">
 </span>    <span class="comment documentation">/// ```</span>
-    <span class="keyword">pub</span> <span class="keyword">const</span> <span class="keyword">fn</span> <span class="function declaration">new</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="struct">Foo</span> <span class="punctuation">{</span>
+    <span class="keyword">pub</span> <span class="keyword">const</span> <span class="keyword">fn</span> <span class="function declaration static">new</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="operator">-&gt;</span> <span class="struct">Foo</span> <span class="punctuation">{</span>
         <span class="struct">Foo</span> <span class="punctuation">{</span> <span class="field">bar</span><span class="punctuation">:</span> <span class="bool_literal">true</span> <span class="punctuation">}</span>
     <span class="punctuation">}</span>
 
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlight_injection.html b/crates/ide/src/syntax_highlighting/test_data/highlight_injection.html
index 18addd00d..57c178916 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlight_injection.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlight_injection.html
@@ -40,7 +40,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 <span class="keyword">fn</span> <span class="function declaration">main</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span>
     <span class="function">fixture</span><span class="punctuation">(</span><span class="string_literal">r#"</span>
         <span class="keyword">trait</span> <span class="trait declaration">Foo</span> <span class="punctuation">{</span>
-            <span class="keyword">fn</span> <span class="function declaration">foo</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span>
+            <span class="keyword">fn</span> <span class="function declaration static">foo</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span>
                 <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"2 + 2 = {}"</span><span class="punctuation">,</span> <span class="numeric_literal">4</span><span class="punctuation">)</span><span class="punctuation">;</span>
             <span class="punctuation">}</span>
         <span class="punctuation">}</span><span class="string_literal">"#</span>
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 2b667b0d4..5c22e2fce 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -513,6 +513,34 @@ fn test_extern_crate() {
     );
 }
 
+#[test]
+fn test_associated_function() {
+    check_highlighting(
+        r#"
+fn not_static() {}
+
+struct foo {}
+
+impl foo {
+    pub fn is_static() {}
+    pub fn is_not_static(&self) {}
+}
+
+trait t {
+    fn t_is_static() {}
+    fn t_is_not_static(&self) {}
+}
+
+impl t for foo {
+    pub fn is_static() {}
+    pub fn is_not_static(&self) {}
+}
+        "#,
+        expect_file!["./test_data/highlight_assoc_functions.html"],
+        false,
+    )
+}
+
 /// Highlights the code given by the `ra_fixture` argument, renders the
 /// result as HTML, and compares it with the HTML file given as `snapshot`.
 /// Note that the `snapshot` file is overwritten by the rendered HTML.