15 files changed, 242 insertions, 46 deletions
diff --git a/Cargo.lock b/Cargo.lock
index 79e632907..68c5f7874 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1155,6 +1155,7 @@ dependencies = [
 "ra_prof 0.1.0",
 "ra_syntax 0.1.0",
 "ra_text_edit 0.1.0",
+ "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
 "rayon 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "relative-path 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/crates/ra_cli/src/main.rs b/crates/ra_cli/src/main.rs
index 93aba4c70..84a1564ce 100644
--- a/crates/ra_cli/src/main.rs
+++ b/crates/ra_cli/src/main.rs
@@ -16,7 +16,10 @@ fn main() -> Result<()> {
        .setting(clap::AppSettings::SubcommandRequiredElseHelp)
        .subcommand(SubCommand::with_name("parse").arg(Arg::with_name("no-dump").long("--no-dump")))
        .subcommand(SubCommand::with_name("symbols"))
-        .subcommand(SubCommand::with_name("highlight"))
+        .subcommand(
+            SubCommand::with_name("highlight")
+                .arg(Arg::with_name("rainbow").short("r").long("rainbow")),
+        )
        .subcommand(
            SubCommand::with_name("analysis-stats")
                .arg(Arg::with_name("verbose").short("v").long("verbose"))
@@ -39,9 +42,9 @@ fn main() -> Result<()> {
                println!("{:?}", s);
            }
        }
-        ("highlight", _) => {
+        ("highlight", Some(matches)) => {
            let (analysis, file_id) = Analysis::from_single_file(read_stdin()?);
-            let html = analysis.highlight_as_html(file_id).unwrap();
+            let html = analysis.highlight_as_html(file_id, matches.is_present("rainbow")).unwrap();
            println!("{}", html);
        }
        ("analysis-stats", Some(matches)) => {
diff --git a/crates/ra_ide_api/Cargo.toml b/crates/ra_ide_api/Cargo.toml
index d399d5e2e..8939e9d79 100644
--- a/crates/ra_ide_api/Cargo.toml
+++ b/crates/ra_ide_api/Cargo.toml
@@ -15,6 +15,7 @@ rustc-hash = "1.0"
 parking_lot = "0.7.0"
 unicase = "2.2.0"
 superslice = "1.0.0"
+rand = "0.6.5"
 jemallocator = { version = "0.1.9", optional = true }
 jemalloc-ctl = { version = "0.2.0", optional = true }
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index d3456d5b2..452407e8e 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -463,8 +463,8 @@ impl Analysis {
    }
    /// Computes syntax highlighting for the given file.
-    pub fn highlight_as_html(&self, file_id: FileId) -> Cancelable<String> {
+    pub fn highlight_as_html(&self, file_id: FileId, rainbow: bool) -> Cancelable<String> {
-        self.with_db(|db| syntax_highlighting::highlight_as_html(db, file_id))
+        self.with_db(|db| syntax_highlighting::highlight_as_html(db, file_id, rainbow))
    }
    /// Computes completions at the given position.
@@ -472,7 +472,7 @@ impl Analysis {
        self.with_db(|db| completion::completions(db, position).map(Into::into))
    }
-    /// Computes assists (aks code actons aka intentions) for the given
+    /// Computes assists (aka code actions aka intentions) for the given
    /// position.
    pub fn assists(&self, frange: FileRange) -> Cancelable<Vec<Assist>> {
        self.with_db(|db| assists::assists(db, frange))
diff --git a/crates/ra_ide_api/src/snapshots/highlighting.html b/crates/ra_ide_api/src/snapshots/highlighting.html
index bfc0a67b1..ebd187a35 100644
--- a/crates/ra_ide_api/src/snapshots/highlighting.html
+++ b/crates/ra_ide_api/src/snapshots/highlighting.html
@@ -1,10 +1,7 @@
 <style>
-pre {
+body       { margin: 0; }
-    color: #DCDCCC;
+pre        { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padding: 0.4em; }
-    background-color: #3F3F3F;
-    font-size: 22px;
-}
 .comment   { color: #7F9F7F; }
 .string    { color: #CC9393; }
@@ -19,10 +16,8 @@ pre {
 .keyword           { color: #F0DFAF; }
 .keyword\.unsafe  { color: #F0DFAF; font-weight: bold; }
 .keyword\.control { color: #DC8CC3; }
 </style>
-<pre><code>
+<pre><code><span class="attribute">#</span><span class="attribute">[</span><span class="attribute">derive</span><span class="attribute">(</span><span class="attribute">Clone</span><span class="attribute">,</span><span class="attribute"> </span><span class="attribute">Debug</span><span class="attribute">)</span><span class="attribute">]</span>
-<span class="attribute">#</span><span class="attribute">[</span><span class="attribute">derive</span><span class="attribute">(</span><span class="attribute">Clone</span><span class="attribute">,</span><span class="attribute"> </span><span class="attribute">Debug</span><span class="attribute">)</span><span class="attribute">]</span>
 <span class="keyword">struct</span> <span class="function">Foo</span> {
    <span class="keyword">pub</span> <span class="function">x</span>: <span class="text">i32</span>,
    <span class="keyword">pub</span> <span class="function">y</span>: <span class="text">i32</span>,
@@ -36,10 +31,9 @@ pre {
 <span class="keyword">fn</span> <span class="function">main</span>() {
    <span class="macro">println</span><span class="macro">!</span>(<span class="string">"Hello, {}!"</span>, <span class="literal">92</span>);
-    <span class="keyword">let</span> <span class="keyword">mut</span> <span class="function">vec</span> = <span class="text">Vec</span>::<span class="text">new</span>();
+    <span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable" data-binding-hash="9636295041291189729" style="color: hsl(51,57%,74%);">vec</span> = <span class="text">Vec</span>::<span class="text">new</span>();
    <span class="keyword.control">if</span> <span class="keyword">true</span> {
-        <span class="text">vec</span>.<span class="text">push</span>(<span class="type">Foo</span> { <span class="field">x</span>: <span class="literal">0</span>, <span class="field">y</span>: <span class="literal">1</span> });
+        <span class="variable" data-binding-hash="8496027264380925433" style="color: hsl(18,48%,55%);">vec</span>.<span class="text">push</span>(<span class="type">Foo</span> { <span class="field">x</span>: <span class="literal">0</span>, <span class="field">y</span>: <span class="literal">1</span> });
    }
-    <span class="keyword.unsafe">unsafe</span> { <span class="text">vec</span>.<span class="text">set_len</span>(<span class="literal">0</span>); }
+    <span class="keyword.unsafe">unsafe</span> { <span class="variable" data-binding-hash="8496027264380925433" style="color: hsl(18,48%,55%);">vec</span>.<span class="text">set_len</span>(<span class="literal">0</span>); }
-}
+}</code></pre>
+\ No newline at end of file
-</code></pre>
-\ No newline at end of file
diff --git a/crates/ra_ide_api/src/snapshots/rainbow_highlighting.html b/crates/ra_ide_api/src/snapshots/rainbow_highlighting.html
new file mode 100644
index 000000000..729d129d0
--- /dev/null
+++ b/crates/ra_ide_api/src/snapshots/rainbow_highlighting.html
@@ -0,0 +1,27 @@
+<style>
+body       { margin: 0; }
+pre        { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padding: 0.4em; }
+.comment   { color: #7F9F7F; }
+.string    { color: #CC9393; }
+.function  { color: #93E0E3; }
+.parameter { color: #94BFF3; }
+.builtin   { color: #DD6718; }
+.text      { color: #DCDCCC; }
+.attribute { color: #BFEBBF; }
+.literal   { color: #DFAF8F; }
+.macro     { color: #DFAF8F; }
+.keyword           { color: #F0DFAF; }
+.keyword\.unsafe  { color: #F0DFAF; font-weight: bold; }
+.keyword\.control { color: #DC8CC3; }
+</style>
+<pre><code><span class="keyword">fn</span> <span class="function">main</span>() {
+    <span class="keyword">let</span> <span class="variable" data-binding-hash="3888301305669440875" style="color: hsl(242,59%,59%);">hello</span> = <span class="string">"hello"</span>;
+    <span class="keyword">let</span> <span class="variable" data-binding-hash="5695551762718493399" style="color: hsl(272,48%,45%);">x</span> = <span class="variable" data-binding-hash="3888301305669440875" style="color: hsl(242,59%,59%);">hello</span>.<span class="text">to_string</span>();
+    <span class="keyword">let</span> <span class="variable" data-binding-hash="5435401749617022797" style="color: hsl(353,77%,74%);">y</span> = <span class="variable" data-binding-hash="3888301305669440875" style="color: hsl(242,59%,59%);">hello</span>.<span class="text">to_string</span>();
+    <span class="keyword">let</span> <span class="variable" data-binding-hash="1903207544374197704" style="color: hsl(58,61%,61%);">x</span> = <span class="string">"other color please!"</span>;
+    <span class="keyword">let</span> <span class="variable" data-binding-hash="14878783531007968800" style="color: hsl(265,73%,83%);">y</span> = <span class="variable" data-binding-hash="1903207544374197704" style="color: hsl(58,61%,61%);">x</span>.<span class="text">to_string</span>();
+}</code></pre>
+\ No newline at end of file
diff --git a/crates/ra_ide_api/src/syntax_highlighting.rs b/crates/ra_ide_api/src/syntax_highlighting.rs
index 87e053364..dcefb0513 100644
--- a/crates/ra_ide_api/src/syntax_highlighting.rs
+++ b/crates/ra_ide_api/src/syntax_highlighting.rs
@@ -1,6 +1,6 @@
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxHashSet, FxHashMap};
-use ra_syntax::{ast, AstNode, TextRange, Direction, SyntaxKind, SyntaxKind::*, SyntaxElement, T};
+use ra_syntax::{ast, AstNode, TextRange, Direction, SmolStr, SyntaxKind, SyntaxKind::*, SyntaxElement, T};
 use ra_db::SourceDatabase;
 use ra_prof::profile;
@@ -10,6 +10,7 @@ use crate::{FileId, db::RootDatabase};
 pub struct HighlightedRange {
    pub range: TextRange,
    pub tag: &'static str,
+    pub binding_hash: Option<u64>,
 }
 fn is_control_keyword(kind: SyntaxKind) -> bool {
@@ -29,22 +30,36 @@ fn is_control_keyword(kind: SyntaxKind) -> bool {
 pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRange> {
    let _p = profile("highlight");
    let source_file = db.parse(file_id);
+    fn calc_binding_hash(file_id: FileId, text: &SmolStr, shadow_count: u32) -> u64 {
+        fn hash<T: std::hash::Hash + std::fmt::Debug>(x: T) -> u64 {
+            use std::{collections::hash_map::DefaultHasher, hash::Hasher};
+            let mut hasher = DefaultHasher::new();
+            x.hash(&mut hasher);
+            hasher.finish()
+        }
+        hash((file_id, text, shadow_count))
+    }
    // Visited nodes to handle highlighting priorities
    let mut highlighted: FxHashSet<SyntaxElement> = FxHashSet::default();
+    let mut bindings_shadow_count: FxHashMap<SmolStr, u32> = FxHashMap::default();
    let mut res = Vec::new();
    for node in source_file.syntax().descendants_with_tokens() {
        if highlighted.contains(&node) {
            continue;
        }
+        let mut binding_hash = None;
        let tag = match node.kind() {
            COMMENT => "comment",
            STRING | RAW_STRING | RAW_BYTE_STRING | BYTE_STRING => "string",
            ATTR => "attribute",
            NAME_REF => {
-                if let Some(name_ref) = node.as_node().and_then(|n| ast::NameRef::cast(n)) {
+                if let Some(name_ref) = node.as_node().and_then(ast::NameRef::cast) {
                    use crate::name_ref_kind::{classify_name_ref, NameRefKind::*};
                    use hir::{ModuleDef, ImplItem};
@@ -68,7 +83,20 @@ pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRa
                        Some(Def(ModuleDef::Trait(_))) => "type",
                        Some(Def(ModuleDef::TypeAlias(_))) => "type",
                        Some(SelfType(_)) => "type",
-                        Some(Pat(_)) => "text",
+                        Some(Pat(ptr)) => {
+                            binding_hash = Some({
+                                let text = ptr
+                                    .syntax_node_ptr()
+                                    .to_node(&source_file.syntax())
+                                    .text()
+                                    .to_smol_string();
+                                let shadow_count =
+                                    bindings_shadow_count.entry(text.clone()).or_default();
+                                calc_binding_hash(file_id, &text, *shadow_count)
+                            });
+                            "variable"
+                        }
                        Some(SelfParam(_)) => "type",
                        Some(GenericParam(_)) => "type",
                        None => "text",
@@ -77,7 +105,24 @@ pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRa
                    "text"
                }
            }
-            NAME => "function",
+            NAME => {
+                if let Some(name) = node.as_node().and_then(ast::Name::cast) {
+                    if name.syntax().ancestors().any(|x| ast::BindPat::cast(x).is_some()) {
+                        binding_hash = Some({
+                            let text = name.syntax().text().to_smol_string();
+                            let shadow_count =
+                                bindings_shadow_count.entry(text.clone()).or_insert(0);
+                            *shadow_count += 1;
+                            calc_binding_hash(file_id, &text, *shadow_count)
+                        });
+                        "variable"
+                    } else {
+                        "function"
+                    }
+                } else {
+                    "text"
+                }
+            }
            TYPE_ALIAS_DEF | TYPE_ARG | TYPE_PARAM => "type",
            INT_NUMBER | FLOAT_NUMBER | CHAR | BYTE => "literal",
            LIFETIME => "parameter",
@@ -85,6 +130,7 @@ pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRa
            k if is_control_keyword(k) => "keyword.control",
            k if k.is_keyword() => "keyword",
            _ => {
+                // let analyzer = hir::SourceAnalyzer::new(db, file_id, name_ref.syntax(), None);
                if let Some(macro_call) = node.as_node().and_then(ast::MacroCall::cast) {
                    if let Some(path) = macro_call.path() {
                        if let Some(segment) = path.segment() {
@@ -101,6 +147,7 @@ pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRa
                                res.push(HighlightedRange {
                                    range: TextRange::from_to(range_start, range_end),
                                    tag: "macro",
+                                    binding_hash: None,
                                })
                            }
                        }
@@ -109,14 +156,25 @@ pub(crate) fn highlight(db: &RootDatabase, file_id: FileId) -> Vec<HighlightedRa
                continue;
            }
        };
-        res.push(HighlightedRange { range: node.range(), tag })
+        res.push(HighlightedRange { range: node.range(), tag, binding_hash })
    }
    res
 }
-pub(crate) fn highlight_as_html(db: &RootDatabase, file_id: FileId) -> String {
+pub(crate) fn highlight_as_html(db: &RootDatabase, file_id: FileId, rainbow: bool) -> String {
    let source_file = db.parse(file_id);
+    fn rainbowify(seed: u64) -> String {
+        use rand::prelude::*;
+        let mut rng = SmallRng::seed_from_u64(seed);
+        format!(
+            "hsl({h},{s}%,{l}%)",
+            h = rng.gen_range::<u16, _, _>(0, 361),
+            s = rng.gen_range::<u16, _, _>(42, 99),
+            l = rng.gen_range::<u16, _, _>(40, 91),
+        )
+    }
    let mut ranges = highlight(db, file_id);
    ranges.sort_by_key(|it| it.range.start());
    // quick non-optimal heuristic to intersect token ranges and highlighted ranges
@@ -138,16 +196,24 @@ pub(crate) fn highlight_as_html(db: &RootDatabase, file_id: FileId) -> String {
            }
        }
        let text = html_escape(&token.text());
-        let classes = could_intersect
+        let ranges = could_intersect
            .iter()
            .filter(|it| token.range().is_subrange(&it.range))
-            .map(|it| it.tag)
            .collect::<Vec<_>>();
-        if classes.is_empty() {
+        if ranges.is_empty() {
            buf.push_str(&text);
        } else {
-            let classes = classes.join(" ");
+            let classes = ranges.iter().map(|x| x.tag).collect::<Vec<_>>().join(" ");
-            buf.push_str(&format!("<span class=\"{}\">{}</span>", classes, text));
+            let binding_hash = ranges.first().and_then(|x| x.binding_hash);
+            let color = match (rainbow, binding_hash) {
+                (true, Some(hash)) => format!(
+                    " data-binding-hash=\"{}\" style=\"color: {};\"",
+                    hash,
+                    rainbowify(hash)
+                ),
+                _ => "".into(),
+            };
+            buf.push_str(&format!("<span class=\"{}\"{}>{}</span>", classes, color, text));
        }
    }
    buf.push_str("</code></pre>");
@@ -161,11 +227,8 @@ fn html_escape(text: &str) -> String {
 const STYLE: &str = "
 <style>
-pre {
+body       { margin: 0; }
-    color: #DCDCCC;
+pre        { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padding: 0.4em; }
-    background-color: #3F3F3F;
-    font-size: 22px;
-}
 .comment   { color: #7F9F7F; }
 .string    { color: #CC9393; }
@@ -180,7 +243,6 @@ pre {
 .keyword           { color: #F0DFAF; }
 .keyword\\.unsafe  { color: #F0DFAF; font-weight: bold; }
 .keyword\\.control { color: #DC8CC3; }
 </style>
 ";
@@ -213,12 +275,36 @@ fn main() {
    }
    unsafe { vec.set_len(0); }
 }
-"#,
+"#
+            .trim(),
        );
        let dst_file = project_dir().join("crates/ra_ide_api/src/snapshots/highlighting.html");
-        let actual_html = &analysis.highlight_as_html(file_id).unwrap();
+        let actual_html = &analysis.highlight_as_html(file_id, true).unwrap();
+        let expected_html = &read_text(&dst_file);
+        std::fs::write(dst_file, &actual_html).unwrap();
+        assert_eq_text!(expected_html, actual_html);
+    }
+    #[test]
+    fn test_rainbow_highlighting() {
+        let (analysis, file_id) = single_file(
+            r#"
+fn main() {
+    let hello = "hello";
+    let x = hello.to_string();
+    let y = hello.to_string();
+    let x = "other color please!";
+    let y = x.to_string();
+}
+"#
+            .trim(),
+        );
+        let dst_file =
+            project_dir().join("crates/ra_ide_api/src/snapshots/rainbow_highlighting.html");
+        let actual_html = &analysis.highlight_as_html(file_id, true).unwrap();
        let expected_html = &read_text(&dst_file);
-        // std::fs::write(dst_file, &actual_html).unwrap();
+        std::fs::write(dst_file, &actual_html).unwrap();
        assert_eq_text!(expected_html, actual_html);
    }
 }
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index a82ae696b..e36db12b3 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -872,7 +872,11 @@ fn highlight(world: &ServerWorld, file_id: FileId) -> Result<Vec<Decoration>> {
        .analysis()
        .highlight(file_id)?
        .into_iter()
-        .map(|h| Decoration { range: h.range.conv_with(&line_index), tag: h.tag })
+        .map(|h| Decoration {
+            range: h.range.conv_with(&line_index),
+            tag: h.tag,
+            binding_hash: h.binding_hash.map(|x| x.to_string()),
+        })
        .collect();
    Ok(res)
 }
diff --git a/crates/ra_lsp_server/src/req.rs b/crates/ra_lsp_server/src/req.rs
index 6090eb7b9..992c24eac 100644
--- a/crates/ra_lsp_server/src/req.rs
+++ b/crates/ra_lsp_server/src/req.rs
@@ -129,6 +129,7 @@ pub struct PublishDecorationsParams {
 pub struct Decoration {
    pub range: Range,
    pub tag: &'static str,
+    pub binding_hash: Option<String>,
 }
 pub enum ParentModule {}
diff --git a/crates/ra_syntax/src/syntax_text.rs b/crates/ra_syntax/src/syntax_text.rs
index b013164c4..c9038cd5c 100644
--- a/crates/ra_syntax/src/syntax_text.rs
+++ b/crates/ra_syntax/src/syntax_text.rs
@@ -1,6 +1,6 @@
 use std::{fmt, ops::{self, Bound}};
-use crate::{SyntaxNode, TextRange, TextUnit, SyntaxElement};
+use crate::{SmolStr, SyntaxNode, TextRange, TextUnit, SyntaxElement};
 #[derive(Clone)]
 pub struct SyntaxText<'a> {
@@ -34,6 +34,12 @@ impl<'a> SyntaxText<'a> {
        self.chunks().collect()
    }
+    pub fn to_smol_string(&self) -> SmolStr {
+        // FIXME: use `self.chunks().collect()` here too once
+        // https://github.com/matklad/smol_str/pull/12 is merged and published
+        self.to_string().into()
+    }
    pub fn contains(&self, c: char) -> bool {
        self.chunks().any(|it| it.contains(c))
    }
diff --git a/docs/user/features.md b/docs/user/features.md
index 22470bc56..b6e6008c4 100644
--- a/docs/user/features.md
+++ b/docs/user/features.md
@@ -470,3 +470,12 @@ There also snippet completions:
 - `tfn` -> `#[test] fn f(){}`
+### Code highlighting
+Experimental feature to let rust-analyzer highlight Rust code instead of using the
+default highlighter.
+#### Rainbow highlighting
+Experimental feature that, given code highlighting using rust-analyzer is
+active, will pick unique colors for identifiers.
diff --git a/editors/code/package-lock.json b/editors/code/package-lock.json
index 29cd260a4..6b3a12f91 100644
--- a/editors/code/package-lock.json
+++ b/editors/code/package-lock.json
@@ -36,6 +36,11 @@
            "integrity": "sha512-Ja7d4s0qyGFxjGeDq5S7Si25OFibSAHUi6i17UWnwNnpitADN7hah9q0Tl25gxuV5R1u2Bx+np6w4LHXfHyj/g==",
            "dev": true
        },
+        "@types/seedrandom": {
+            "version": "2.4.28",
+            "resolved": "https://registry.npmjs.org/@types/seedrandom/-/seedrandom-2.4.28.tgz",
+            "integrity": "sha512-SMA+fUwULwK7sd/ZJicUztiPs8F1yCPwF3O23Z9uQ32ME5Ha0NmDK9+QTsYE4O2tHXChzXomSWWeIhCnoN1LqA=="
+        },
        "agent-base": {
            "version": "4.2.1",
            "resolved": "https://registry.npmjs.org/agent-base/-/agent-base-4.2.1.tgz",
@@ -984,6 +989,11 @@
            "integrity": "sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg==",
            "dev": true
        },
+        "seedrandom": {
+            "version": "3.0.1",
+            "resolved": "https://registry.npmjs.org/seedrandom/-/seedrandom-3.0.1.tgz",
+            "integrity": "sha512-1/02Y/rUeU1CJBAGLebiC5Lbo5FnB22gQbIFFYTLkwvp1xdABZJH1sn4ZT1MzXmPpzv+Rf/Lu2NcsLJiK4rcDg=="
+        },
        "semver": {
            "version": "5.7.0",
            "resolved": "https://registry.npmjs.org/semver/-/semver-5.7.0.tgz",
diff --git a/editors/code/package.json b/editors/code/package.json
index cde5fbcb8..05c808394 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -31,11 +31,13 @@
        "singleQuote": true
    },
    "dependencies": {
+        "seedrandom": "^3.0.1",
        "vscode-languageclient": "^5.3.0-next.4"
    },
    "devDependencies": {
        "@types/mocha": "^5.2.6",
        "@types/node": "^10.14.5",
+        "@types/seedrandom": "^2.4.28",
        "prettier": "^1.17.0",
        "shx": "^0.3.1",
        "tslint": "^5.16.0",
@@ -162,6 +164,11 @@
                    "default": false,
                    "description": "Highlight Rust code (overrides built-in syntax highlighting)"
                },
+                "rust-analyzer.rainbowHighlightingOn": {
+                    "type": "boolean",
+                    "default": false,
+                    "description": "When highlighting Rust code, use a unique color per identifier"
+                },
                "rust-analyzer.showWorkspaceLoadedNotification": {
                    "type": "boolean",
                    "default": true,
diff --git a/editors/code/src/config.ts b/editors/code/src/config.ts
index 481a5e5f1..8d73a6b34 100644
--- a/editors/code/src/config.ts
+++ b/editors/code/src/config.ts
@@ -15,6 +15,7 @@ export interface CargoWatchOptions {
 export class Config {
    public highlightingOn = true;
+    public rainbowHighlightingOn = false;
    public enableEnhancedTyping = true;
    public raLspServerPath = RA_LSP_DEBUG || 'ra_lsp_server';
    public showWorkspaceLoadedNotification = true;
@@ -39,6 +40,12 @@ export class Config {
            this.highlightingOn = config.get('highlightingOn') as boolean;
        }
+        if (config.has('rainbowHighlightingOn')) {
+            this.rainbowHighlightingOn = config.get(
+                'rainbowHighlightingOn'
+            ) as boolean;
+        }
        if (config.has('showWorkspaceLoadedNotification')) {
            this.showWorkspaceLoadedNotification = config.get(
                'showWorkspaceLoadedNotification'
diff --git a/editors/code/src/highlighting.ts b/editors/code/src/highlighting.ts
index 8389d94b8..52a0bd4bb 100644
--- a/editors/code/src/highlighting.ts
+++ b/editors/code/src/highlighting.ts
@@ -1,3 +1,4 @@
+import seedrandom = require('seedrandom');
 import * as vscode from 'vscode';
 import * as lc from 'vscode-languageclient';
@@ -6,6 +7,20 @@ import { Server } from './server';
 export interface Decoration {
    range: lc.Range;
    tag: string;
+    bindingHash?: string;
+}
+// Based on this HSL-based color generator: https://gist.github.com/bendc/76c48ce53299e6078a76
+function fancify(seed: string, shade: 'light' | 'dark') {
+    const random = seedrandom(seed);
+    const randomInt = (min: number, max: number) => {
+        return Math.floor(random() * (max - min + 1)) + min;
+    };
+    const h = randomInt(0, 360);
+    const s = randomInt(42, 98);
+    const l = shade === 'light' ? randomInt(15, 40) : randomInt(40, 90);
+    return `hsl(${h},${s}%,${l}%)`;
 }
 export class Highlighter {
@@ -76,6 +91,9 @@ export class Highlighter {
        }
        const byTag: Map<string, vscode.Range[]> = new Map();
+        const colorfulIdents: Map<string, vscode.Range[]> = new Map();
+        const rainbowTime = Server.config.rainbowHighlightingOn;
        for (const tag of this.decorations.keys()) {
            byTag.set(tag, []);
        }
@@ -84,9 +102,23 @@ export class Highlighter {
            if (!byTag.get(d.tag)) {
                continue;
            }
-            byTag
-                .get(d.tag)!
+            if (rainbowTime && d.bindingHash) {
-                .push(Server.client.protocol2CodeConverter.asRange(d.range));
+                if (!colorfulIdents.has(d.bindingHash)) {
+                    colorfulIdents.set(d.bindingHash, []);
+                }
+                colorfulIdents
+                    .get(d.bindingHash)!
+                    .push(
+                        Server.client.protocol2CodeConverter.asRange(d.range)
+                    );
+            } else {
+                byTag
+                    .get(d.tag)!
+                    .push(
+                        Server.client.protocol2CodeConverter.asRange(d.range)
+                    );
+            }
        }
        for (const tag of byTag.keys()) {
@@ -96,5 +128,13 @@ export class Highlighter {
            const ranges = byTag.get(tag)!;
            editor.setDecorations(dec, ranges);
        }
+        for (const [hash, ranges] of colorfulIdents.entries()) {
+            const dec = vscode.window.createTextEditorDecorationType({
+                light: { color: fancify(hash, 'light') },
+                dark: { color: fancify(hash, 'dark') }
+            });
+            editor.setDecorations(dec, ranges);
+        }
    }
 }