PythonErrors.kt

src/jvmMain/kotlin/afield/lang/python/PythonErrors.kt · 60 lines

Error locations for Python boxes: the cell line that raised, read from the exception's traceback.

PythonErrors holds the Python helper spliced into the interpreter and the Kotlin arithmetic that maps its answer onto a box line. PythonErrorsTest runs the helper under a plain python3.

package afield.lang.python

object PythonErrors

Where a Python box's error happened, found from the exception itself rather than from JEP's message.

A Kotlin box puts the red marker on the line that failed. A Python box used to guess: the JEP message carries no usable line (its Java stack trace reports line 1 for everything run through exec), and the syntax-error pattern expected a <string> filename that cells stopped using when they were compiled as <repl:{box id}>. So every runtime error, and most syntax errors, were marked on the fragment's first line.

SOURCE is spliced into the interpreter's startup text and kept free of Kotlin templates, so PythonErrorsTest runs exactly this text under a plain python3. It defines _field_error_location(exc, filename), which returns [line, type name, message]:

• a SyntaxError raised while compiling the cell reports its own lineno;
• any other exception reports the innermost traceback frame whose code was compiled from the cell (filename) — so an error inside a function the cell defined is marked on the line in that function, and an error inside a library is marked on the cell line that called into it;
• line is -1 when no frame belongs to the cell.

Lines are 1-based within the fragment that ran. boxLine turns one into the box line the output area expects, by the same rule print uses (thisLineOffset + f_lineno).

object PythonErrors {

fun boxLine(pythonLine: Int, fragmentStart: Int, droppedLeadingBlank: Int = 0): Int

The fragment line pythonLine as a box line, or -1 (the fragment's end) when unknown.

    fun boxLine(pythonLine: Int, fragmentStart: Int, droppedLeadingBlank: Int = 0): Int =
        if (pythonLine <= 0) -1 else fragmentStart + pythonLine + droppedLeadingBlank

fun describe(type: String, message: String): String

The text shown beside the marker: NameError: name 'q' is not defined.

    fun describe(type: String, message: String): String =
        if (message.isBlank()) type else "$type: $message"

val SOURCE: String = """

# ---------- error locations: which line of the cell raised ----------
def _field_error_location(exc, filename):
    try:
        if isinstance(exc, SyntaxError) and getattr(exc, "filename", None) == filename and exc.lineno:
            return [int(exc.lineno), type(exc).__name__, str(exc.msg or "")]
        line = -1
        tb = exc.__traceback__
        while tb is not None:
            if tb.tb_frame.f_code.co_filename == filename:
                line = int(tb.tb_lineno)
            tb = tb.tb_next
        return [line, type(exc).__name__, str(exc)]
    except BaseException:
        return [-1, type(exc).__name__, ""]
"""
}