Semantic highlighting spike

Very simple approach: For each identifier, set the hash of the range
where it's defined as its 'id' and use it in the VSCode extension to
generate unique colors.

Thus, the generated colors are per-file. They are also quite fragile,
and I'm not entirely sure why. Looks like we need to make sure the
same ranges aren't overwritten by a later request?

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;
+    id?: 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 +91,8 @@ export class Highlighter {
         }
 
         const byTag: Map<string, vscode.Range[]> = new Map();
+        const colorfulIdents: Map<string, vscode.Range[]> = new Map();
+
         for (const tag of this.decorations.keys()) {
             byTag.set(tag, []);
         }
@@ -84,9 +101,23 @@ export class Highlighter {
             if (!byTag.get(d.tag)) {
                 continue;
             }
-            byTag
-                .get(d.tag)!
-                .push(Server.client.protocol2CodeConverter.asRange(d.range));
+
+            if (d.id) {
+                if (!colorfulIdents.has(d.id)) {
+                    colorfulIdents.set(d.id, []);
+                }
+                colorfulIdents
+                    .get(d.id)!
+                    .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 +127,13 @@ 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);
+        }
     }
 }