LSP: Implements goto-definition.

test/libsolidity/lsp/goto_definition.sol

@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+import "./lib.sol";
+
+interface I
+{
+    function f(uint x) external returns (uint);
+}
+
+contract IA is I
+{
+    function f(uint x) public pure override returns (uint) { return x + 1; }
+}
+
+contract IB is I
+{
+    function f(uint x) public pure override returns (uint) { return x + 2; }
+}
+
+library IntLib
+{
+    function add(int self, int b) public pure returns (int) { return self + b; }
+}
+
+contract C
+{
+    I obj;
+    function virtual_inheritance() public payable
+    {
+        obj = new IA();
+        obj.f(1); // goto-definition should jump to definition of interface.
+    }
+
+    using IntLib for *;
+    function using_for(int i) pure public
+    {
+        i.add(5);
+        14.add(4);
+    }
+
+    function useLib(uint n) public payable returns (uint)
+    {
+        return Lib.add(n, 1);
+    }
+
+    function enums(Color c) public pure returns (Color d)
+    {
+        Color e = Color.Red;
+        if (c == e)
+            d = Color.Green;
+        else
+            d = c;
+    }
+
+    type Price is uint128;
+    function udlTest() public pure returns (uint128)
+    {
+        Price p = Price.wrap(128);
+        return Price.unwrap(p);
+    }
+
+    function structCtorTest(uint8 v) public pure returns (uint8 result)
+    {
+        RGBColor memory c = RGBColor(v, 2 * v, 3 * v);
+        result = c.red;
+    }
+}

test/libsolidity/lsp/goto_definition_imports.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.8.0;
+
+import {Weather as Wetter} from "./lib.sol";
+import "./lib.sol" as That;
+
+contract C
+{
+    function test_symbol_alias() public pure returns (Wetter result)
+    {
+        result = Wetter.Sunny;
+    }
+
+    function test_library_alias() public pure returns (That.Color result)
+    {
+        That.Color color = That.Color.Red;
+        result = color;
+    }
+}

test/libsolidity/lsp/lib.sol

@@ -1,6 +1,25 @@
 // SPDX-License-Identifier: UNLICENSED
 pragma solidity >=0.8.0;
 
+/// Some Error type E.
+error E(uint, uint);
+
+enum Weather {
+    Sunny,
+    Cloudy,
+    Rainy
+}
+
+/// Some custom Color enum type holding 3 colors.
+enum Color {
+    /// Red color.
+    Red,
+    /// Green color.
+    Green,
+    /// Blue color.
+    Blue
+}
+
 library Lib
 {
     function add(uint a, uint b) public pure returns (uint result)
@@ -13,3 +32,10 @@ library Lib
         uint unused;
     }
 }
+
+struct RGBColor
+{
+    uint8 red;
+    uint8 green;
+    uint8 blue;
+}