feat: add vm.unixTime to VmSafe interface (#465)

* Add vm.unixTime to VmSafe interface

* Change VmSafe.unixTime signature return to uint256

* chore: tweak vm layout

---------

Co-authored-by: Matt Solomon <[email protected]>

Author: Tudmotu

src/Vm.sol

@@ -146,7 +146,7 @@ interface VmSafe {
     // Suspends execution of the main thread for `duration` milliseconds
     function sleep(uint256 duration) external;
 
-    // ======== Filesystem ========
+    // ======== OS and Filesystem ========
 
     // -------- Metadata --------
 
@@ -165,6 +165,9 @@ interface VmSafe {
     // Get the path of the current project root.
     function projectRoot() external view returns (string memory path);
 
+    // Returns the time since unix epoch in milliseconds
+    function unixTime() external returns (uint256 milliseconds);
+
     // -------- Reading and writing --------
 
     // Closes file for reading, resetting the offset and allowing to read it from beginning with readLine.
@@ -238,6 +241,14 @@ interface VmSafe {
     // `path` is relative to the project root.
     function writeLine(string calldata path, string calldata data) external;
 
+    // -------- Foreign Function Interface --------
+
+    // Performs a foreign function call via the terminal
+    function ffi(string[] calldata commandInput) external returns (bytes memory result);
+
+    // Performs a foreign function call via terminal and returns the exit code, stdout, and stderr
+    function tryFfi(string[] calldata commandInput) external returns (FfiResult memory result);
+
     // ======== Environment Variables ========
 
     // Sets environment variables
@@ -317,14 +328,6 @@ interface VmSafe {
     // Signs data, (Wallet, digest) => (v, r, s)
     function sign(Wallet calldata wallet, bytes32 digest) external returns (uint8 v, bytes32 r, bytes32 s);
 
-    // ======== External Interactions ========
-
-    // Performs a foreign function call via the terminal
-    function ffi(string[] calldata commandInput) external returns (bytes memory result);
-
-    // Performs a foreign function call via terminal and returns the exit code, stdout, and stderr
-    function tryFfi(string[] calldata commandInput) external returns (FfiResult memory result);
-
     // ======== Scripts ========
 
     // -------- Broadcasting Transactions --------

test/Vm.t.sol

@@ -9,7 +9,7 @@ contract VmTest is Test {
     // inadvertently moved between Vm and VmSafe. This test must be updated each time a function is
     // added to or removed from Vm or VmSafe.
     function test_interfaceId() public {
-        assertEq(type(VmSafe).interfaceId, bytes4(0x50ccd9ad), "VmSafe");
+        assertEq(type(VmSafe).interfaceId, bytes4(0x329f5e71), "VmSafe");
         assertEq(type(Vm).interfaceId, bytes4(0x82ccbb14), "Vm");
     }
 }