compiler: add nicer error handling

- vm: fix pop opcode handler

src/compiler.zig

@@ -337,8 +337,24 @@ pub const Compiler = struct {
         try self.emitByte(OpCode.Pop);
     }
 
+    fn synchronize(self: *Compiler) !void {
+        self.parser.panicMode = false;
+
+        while (self.parser.current.ttype != .EOF) {
+            if (self.parser.previous.ttype == .SEMICOLON) return;
+
+            switch (self.parser.current.ttype) {
+                .CLASS, .FUN, .VAR, .FOR, .IF, .WHILE, .PRINT, .RETURN => return,
+                else => {},
+            }
+
+            try self.advance();
+        }
+    }
+
     fn declaration(self: *Compiler) !void {
         try self.statement();
+        if (self.parser.panicMode) try self.synchronize();
     }
 
     fn statement(self: *Compiler) !void {

src/vm.zig

@@ -255,7 +255,10 @@ pub const VM = struct {
                 chunk.OpCode.True => try self.push(values.BoolVal(true)),
                 chunk.OpCode.False => try self.push(values.BoolVal(false)),
 
-                chunk.OpCode.Pop => self.pop(),
+                chunk.OpCode.Pop => blk: {
+                    _ = self.pop();
+                    break :blk;
+                },
 
                 chunk.OpCode.Equal => blk: {
                     var a = self.pop();