Add documents storage

Currently using a StringHashMap to store the different project documents. Might investigate into doing some caching later down the line.

src/lsp/document_store.zig

@@ -0,0 +1,60 @@
+const std = @import("std");
+
+/// Stores the latest contents of each open text document.
+pub const DocumentStore = struct {
+    allocator: std.mem.Allocator,
+    entries: std.StringHashMap(Document),
+
+    /// Snapshot of a document's contents and version.
+    pub const Document = struct {
+        text: []u8,
+        version: i64,
+    };
+
+    /// Creates an empty store backed by the provided allocator.
+    pub fn init(allocator: std.mem.Allocator) DocumentStore {
+        return .{ .allocator = allocator, .entries = std.StringHashMap(Document).init(allocator) };
+    }
+
+    /// Releases all tracked documents and frees associated memory.
+    pub fn deinit(self: *DocumentStore) void {
+        var it = self.entries.iterator();
+        while (it.next()) |entry| {
+            self.allocator.free(entry.key_ptr.*);
+            self.allocator.free(entry.value_ptr.text);
+        }
+        self.entries.deinit();
+        self.* = undefined;
+    }
+
+    /// Inserts or replaces the document at `uri` with the given text and version.
+    pub fn upsert(self: *DocumentStore, uri: []const u8, version: i64, text: []const u8) !void {
+        const gop = try self.entries.getOrPut(uri);
+        if (!gop.found_existing) {
+            gop.key_ptr.* = try self.allocator.dupe(u8, uri);
+        } else {
+            self.allocator.free(gop.value_ptr.text);
+        }
+
+        gop.value_ptr.* = .{
+            .text = try self.allocator.dupe(u8, text),
+            .version = version,
+        };
+    }
+
+    /// Removes a document from the store, if present.
+    pub fn remove(self: *DocumentStore, uri: []const u8) void {
+        if (self.entries.fetchRemove(uri)) |removed| {
+            self.allocator.free(removed.key);
+            self.allocator.free(removed.value.text);
+        }
+    }
+
+    /// Returns the stored document (if any). The returned slice references memory owned by the store.
+    pub fn get(self: *DocumentStore, uri: []const u8) ?Document {
+        if (self.entries.get(uri)) |doc| {
+            return doc;
+        }
+        return null;
+    }
+};