From d761f509f2e0ea2503f7f75014e396cb6bb26802 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <koszko@koszko.org>
Date: Wed, 14 Feb 2024 23:13:36 +0100
Subject: Initial commit.

---
 trace-preamble.js | 146 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)
 create mode 100644 trace-preamble.js

(limited to 'trace-preamble.js')

diff --git a/trace-preamble.js b/trace-preamble.js
new file mode 100644
index 00000000..75c899d0
--- /dev/null
+++ b/trace-preamble.js
@@ -0,0 +1,146 @@
+const tracing = (() => {
+    const log = [];
+    const objects = new Map();
+
+    let call_stack_top = null;
+
+    function record_value(log_entry, name, value, as_array=false) {
+        log_entry[name] = value;
+
+        for (const _value of as_array? value : [value]) {
+            if (_value !== null && _value !== undefined
+                && _value !== false && _value !== true) {
+                const relevant_log_entries = objects.get(_value) || [];
+
+                relevant_log_entries.push(log_entry);
+                objects.set(_value, relevant_log_entries);
+            }
+        }
+
+        return value;
+    }
+
+    function with_log_entry(op_name, line, column, cb) {
+        const log_entry = {
+            op_name, line, column,
+            id: log.length,
+            parent_call: call_stack_top
+        };
+        const saved_stack_top = call_stack_top;
+
+        log.push(log_entry);
+
+        call_stack_top = log_entry;
+
+        try {
+            return cb(log_entry);
+        } catch(ex) {
+            record_value(log_entry, "error", ex);
+
+            throw ex;
+        } finally {
+            call_stack_top = saved_stack_top;
+        }
+    }
+
+    return {
+        get_objects: () => objects,
+
+        get_log: () => log,
+
+        record_binary: function(line, column, operation_name, operation,
+                                left_producer, right_producer) {
+            function go(log_entry) {
+                const left = record_value(log_entry, "left", left_producer());
+
+                const right = record_value(log_entry,
+                                           "right",
+                                           right_producer());
+
+                const result = operation(left, right);
+
+                return record_value(log_entry, "result", result);
+            }
+
+            return with_log_entry(operation_name, line, column, go);
+        },
+
+        record_lazy_binary: function(line, column, operation_name, operation,
+                                     left_producer, right_producer) {
+            function go(log_entry) {
+                const left = record_value(log_entry, "left", left_producer());
+
+                const result = operation(left, right_producer);
+
+                return record_value(log_entry, "result", result);
+            }
+
+            return with_log_entry(operation_name, line, column, go);
+        },
+
+        record_call: function(line, column, function_producer, optional,
+                              args_producer) {
+            function go(log_entry) {
+                const function_object = record_value(log_entry,
+                                                     "function_object",
+                                                     function_producer());
+
+                const record_args = () => record_value(log_entry,
+                                                       "args",
+                                                       args_producer(),
+                                                       true);
+
+                const result = optional ?
+                      function_object?.(...record_args()) :
+                      function_object(...record_args());
+
+                return record_value(log_entry, "result", result);
+            }
+
+            return with_log_entry("call", line, column, go);
+        },
+
+        record_prop_call: function(line, column, this_producer,
+                                   property_optional, property_producer,
+                                   optional, args_producer) {
+            function go(log_entry) {
+                const bound_this = record_value(log_entry,
+                                                "bound_this",
+                                                this_producer());
+
+                const record_property = () => record_value(
+                    log_entry, "property", property_producer()
+                );
+
+                const function_object =
+                      record_value(log_entry,
+                                   "function_object",
+                                   property_optional ?
+                                   bound_this?.[record_property()] :
+                                   bound_this[record_property()]);
+
+                if ((function_object === null ||
+                     function_object === undefined) &&
+                    optional)
+                    return undefined;
+
+                const record_args = () => record_value(log_entry,
+                                                       "args",
+                                                       args_producer(),
+                                                       true);
+
+                const result = Function.apply.call(function_object,
+                                                   bound_this,
+                                                   record_args());
+
+                return record_value(log_entry, "result", result);
+            }
+
+            return with_log_entry(
+                `obj${property_optional}[prop]${optional}() call`,
+                line, column,
+                go
+            );
+        }
+    };
+})();
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