📝 Add docstrings to codex/extend-.perf-budget.yml-with-navigation-thresholds (#285)

Docstrings generation was requested by @shayancoin.

* #126 (comment)

The following files were modified:

* `tools/perf/check-canary-metrics.py`

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: coderabbitai[bot]

tools/perf/check-canary-metrics.py

@@ -36,11 +36,23 @@
 
 
 def exit_success(message: str) -> None:
+    """
+    Prints a message to standard output and exits the process with status code 0.
+    
+    Parameters:
+        message (str): Text to print before exiting.
+    """
     print(message)
     sys.exit(0)
 
 
 def exit_failure(message: str) -> None:
+    """
+    Prints an error message to standard error and terminates the process with exit code 1.
+    
+    Parameters:
+        message (str): Error message to emit to stderr before exiting.
+    """
     print(message, file=sys.stderr)
     sys.exit(1)
 
@@ -56,6 +68,15 @@ def exit_failure(message: str) -> None:
 
 
 def query_prometheus(url: str, query: str) -> Optional[float]:
+    """
+    Query a Prometheus HTTP API for an instant vector and extract the first numeric value.
+    
+    Returns:
+        The numeric value from the first result row as a float, or `None` if Prometheus returned no results.
+    
+    Raises:
+        RuntimeError: If the HTTP request fails, Prometheus responds with a non-"success" status, or the response payload has an unexpected format.
+    """
     encoded_query = urllib.parse.urlencode({'query': query})
     endpoint = f"{url.rstrip('/')}/api/v1/query?{encoded_query}"
     try:
@@ -77,6 +98,16 @@ def query_prometheus(url: str, query: str) -> Optional[float]:
 
 
 def render_query(template: str, build: str) -> str:
+    """
+    Substitutes the `$BUILD` placeholder in a query template with the provided build identifier.
+    
+    Parameters:
+        template (str): Prometheus query template containing the `$BUILD` placeholder.
+        build (str): Build identifier to substitute into the template.
+    
+    Returns:
+        rendered (str): The query string with `$BUILD` replaced by `build`.
+    """
     return template.replace('$BUILD', build)
 
 
@@ -104,6 +135,20 @@ def evaluate_metric(
     unit: str,
     description: str,
 ) -> MetricResult:
+    """
+    Evaluate a single canary metric against an absolute threshold and an optional regression allowance.
+    
+    Parameters:
+        name (str): Human-readable metric identifier used in messages and the resulting MetricResult.name.
+        template (str): Prometheus query template; the placeholder `$BUILD` will be replaced with the build SHA.
+        threshold (float): Absolute budget value the current metric must be less than or equal to.
+        regression_pct (float): Allowed relative increase over the previous build (e.g., 0.1 for 10%); ignored when previous baseline is near zero or unavailable.
+        unit (str): Unit string appended to numeric values in human-readable messages (e.g., "ms", or empty).
+        description (str): Short textual description stored on the MetricResult.description for reporting.
+    
+    Returns:
+        MetricResult: Populated result containing current and optional previous values, threshold and regression parameters, a pass/fail flag, and a human-readable message explaining the outcome.
+    """
     current_query = render_query(template, CURRENT_BUILD)
     current_value = query_prometheus(PROMETHEUS_URL, current_query)
     previous_value = None
@@ -161,6 +206,15 @@ def evaluate_metric(
 
 
 def maybe_check_tempo() -> Optional[MetricResult]:
+    """
+    Check Tempo for traces slower than the configured threshold for the canary service.
+    
+    If TEMPO_URL is unset the function prints a skip message and returns None. Otherwise it queries Tempo for any trace with duration at or above TEMPO_SLOW_TRACE_THRESHOLD_MS within TEMPO_LOOKBACK_SECONDS for TEMPO_SERVICE and produces a MetricResult summarizing whether slow traces were found.
+    
+    Returns:
+        MetricResult: a result named 'tempo_slow_traces' where `passed` is `False` if a slow trace was found and `current_value` is the slow-threshold in milliseconds (or `0.0` if none was found).
+        None: if TEMPO_URL is not configured.
+    """
     if not TEMPO_URL:
         print('TEMPO_URL not provided; skipping trace regression checks.')
         return None
@@ -237,11 +291,28 @@ def maybe_check_tempo() -> Optional[MetricResult]:
 
 
 def write_junit(results_list: list[MetricResult]) -> None:
+    """
+    Write a JUnit-format XML report summarizing the provided MetricResult entries and save it to the configured artifacts location.
+    
+    Each MetricResult becomes a <testcase>; passing results include a <system-out> block with metric details, failing results include a <failure> element and the same details. The file is written to RESULT_DIR/JUNIT_FILENAME and a message with the written path is printed.
+     
+    Parameters:
+        results_list (list[MetricResult]): List of metric results to include in the JUnit report.
+    """
     tests = len(results_list)
     failures_count = len([result for result in results_list if not result.passed])
     suite_name = 'canary-budget'
 
     def xml_escape(value: str) -> str:
+        """
+        Escape characters in a string so it is safe to include in XML content.
+        
+        Parameters:
+            value (str): The raw string to escape.
+        
+        Returns:
+            str: The input string with XML special characters replaced by their entity equivalents (`&amp;`, `&quot;`, `&apos;`, `&lt;`, `&gt;`).
+        """
         return (
             value.replace('&', '&amp;')
             .replace('"', '&quot;')
@@ -292,4 +363,4 @@ def xml_escape(value: str) -> str:
 if failures:
     exit_failure('Canary metrics exceeded budgets; see log for details.')
 
-exit_success('Canary metrics are within budgets.')
+exit_success('Canary metrics are within budgets.')