Refactor how py-script are executed, kill scriptQueue store, introduce pyExec (#881)

Yet another refactoring to untangle the old mess.
Highlights:

base.ts, pyscript.ts and pyrepl.ts were a tangled mess of code, in which each of them interacted with the others in non-obvious ways. Now PyScript is no longer a subclass of BaseEvalElement and it is much simpler. I removed code for handling the attributes std-out and std-err because they are no longer needed with the new display() logic.

The logic for executing python code is now in pyexec.ts: so we are decoupling the process of "finding" the python code (handled by the py-script web component) and the logic to actually execute it. This has many advantages, including the fact that it will be more easily usable by other components (e.g. pyrepl). Also, note that it's called pyexec and not pyeval: in the vast majority of cases in Python you have statements to execute, and almost never expressions to evaluate.

I killed the last remaining global store, scriptQueue tada. As a bonus effect, now we automatically do the correct thing when a <py-script> tag is dynamically added to the DOM (I added a test for it). I did not remove svelte from packages.json, because I don't fully understand the implications: there are various options which mention svelte in rollup.js and tsconfig.json, so it's probably better to kill it in its own PR.

pyexec.ts is also responsible of handling the default target for display() and correct handling/visualization of exceptions. I fixed/improved/added display/output tests in the process.
I also found a problem though, see issue #878, so I improved the test and marked it as xfail.

I removed BaseEvalElement as the superclass of most components. Now the only class which inherits from it is PyRepl. In a follow-up PR, I plan to merge them into a single class and do more cleanup.

During the refactoring, I killed guidGenerator: now instead of generating random py-* IDs which are very hard to read for humans, we generated py-internal-X IDs, where X is 0, 1, 2, 3, etc. This makes writing tests and debugging much easier.

I improved a lot our test machinery: it turns out that PR #829 broke the ability to use/view sourcemaps inside the playwright browser (at least on my machine).
For some reason chromium is unable to find sourcemaps if you use playwrights internal routing. So I reintroduced the http_server fixture which was removed by that PR, and added a pytest option --no-fake-server to use it instead, useful for debugging. By default we are still using the fakeserver though (which is faster and parallelizable).

Similarly, I added --dev which implies --headed and also automatically open chrome dev tools.

pyscriptjs/tests/integration/test_01_basic.py

@@ -1,5 +1,3 @@
-import re
-
 from .support import PyScriptTest
 
 
@@ -8,16 +6,39 @@ class TestBasic(PyScriptTest):
         self.pyscript_run(
             """
             <py-script>
-                display('hello pyscript')
+                print('hello pyscript')
+            </py-script>
+            """
+        )
+        assert self.console.log.lines == [
+            self.PY_COMPLETE,
+            "hello pyscript",
+        ]
+
+    def test_python_exception(self):
+        self.pyscript_run(
+            """
+            <py-script>
+                print('hello pyscript')
+                raise Exception('this is an error')
             </py-script>
         """
         )
-        # this is a very ugly way of checking the content of the DOM. If we
-        # find ourselves to write a lot of code in this style, we will
-        # probably want to write a nicer API for it.
-        inner_html = self.page.locator("py-script").inner_html()
-        pattern = r'<div id="py-.*">hello pyscript</div>'
-        assert re.search(pattern, inner_html)
+        assert self.console.log.lines == [self.PY_COMPLETE, "hello pyscript"]
+        # check that we sent the traceback to the console
+        tb_lines = self.console.error.lines[-1].splitlines()
+        assert tb_lines[0] == "[pyexec] Python exception:"
+        assert tb_lines[1] == "Traceback (most recent call last):"
+        assert tb_lines[-1] == "Exception: this is an error"
+        #
+        # check that we show the traceback in the page. Note that here we
+        # display the "raw" python traceback, without the "[pyexec] Python
+        # exception:" line (which is useful in the console, but not for the
+        # user)
+        pre = self.page.locator("py-script > pre")
+        tb_lines = pre.inner_text().splitlines()
+        assert tb_lines[0] == "Traceback (most recent call last):"
+        assert tb_lines[-1] == "Exception: this is an error"
 
     def test_execution_in_order(self):
         """
@@ -118,3 +139,35 @@ class TestBasic(PyScriptTest):
             "Loaded asciitree",  # printed by pyodide
             "hello asciitree",  # printed by us
         ]
+
+    def test_dynamically_add_py_script_tag(self):
+        self.pyscript_run(
+            """
+            <script>
+                function addPyScriptTag() {
+                    let tag = document.createElement('py-script');
+                    tag.innerHTML = "print('hello world')";
+                    document.body.appendChild(tag);
+                }
+            </script>
+            <button onclick="addPyScriptTag()">Click me</button>
+            """
+        )
+        self.page.locator("button").click()
+        self.page.locator("py-script")  # wait until <py-script> appears
+        assert self.console.log.lines == [
+            self.PY_COMPLETE,
+            "hello world",
+        ]
+
+    def test_py_script_src_attribute(self):
+        self.writefile("foo.py", "print('hello from foo')")
+        self.pyscript_run(
+            """
+            <py-script src="foo.py"></py-script>
+            """
+        )
+        assert self.console.log.lines == [
+            self.PY_COMPLETE,
+            "hello from foo",
+        ]