chore(testing): enforce semgrep gate for suppressed exceptions
Fix broken escape hatch mechanism and address reviewer feedback: - Replace non-functional comment-based pattern-not clauses with Semgrep's native # nosemgrep mechanism for the escape hatch. Semgrep strips comments from the AST so pattern-not clauses matching inline comments never fire; # nosemgrep is the only reliable per-line suppression mechanism. - Require both # nosemgrep: <rule-id> AND # error-propagation: allow on the same line: the former is the actual suppression, the latter is the mandatory human-readable audit annotation. - Add raise $EXC from $CAUSE pattern-not entries for both Exception and BaseException variants to prevent false positives on legitimate exception chaining (raise ServiceError from e). - Switch nox -s lint Semgrep invocation to audit mode (no --error) for the phased rollout: the codebase has ~337 existing suppressions that must be triaged before enforcement mode is enabled. A comment in noxfile.py documents the migration path and references #9103. - Update CONTRIBUTING.md examples and enforcement description to reflect the dual-comment requirement.
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+14
-30
@@ -98,16 +98,6 @@ rules:
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...
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except Exception as $VAR:
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raise $VAR from $CAUSE
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- pattern-not: |
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try:
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...
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except Exception: # error-propagation: allow
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...
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- pattern-not: |
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try:
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...
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except Exception as $VAR: # error-propagation: allow
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...
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- patterns:
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- pattern: |
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try:
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@@ -144,29 +134,23 @@ rules:
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...
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except BaseException as $VAR:
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raise $VAR from $CAUSE
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- pattern-not: |
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try:
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...
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except BaseException: # error-propagation: allow
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...
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- pattern-not: |
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try:
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...
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except BaseException as $VAR: # error-propagation: allow
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...
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message: >
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Broad exception suppression detected. Do not suppress Exception or BaseException
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without re-raising or narrowing to a specific exception type.
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CRITICAL: Let exceptions propagate to top-level execution (see CONTRIBUTING.md).
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If you have specific recovery logic that justifies suppressing this exception,
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add the annotation '# error-propagation: allow' on the except line to disable this rule.
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To suppress this rule for a justified case, add the following inline comment on
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the except line:
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# nosemgrep: python-no-suppressed-exception # error-propagation: allow
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The '# nosemgrep' comment is the actual suppression mechanism (Semgrep native).
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The '# error-propagation: allow' annotation is required for human auditability.
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Example of allowed suppression:
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try:
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resource.cleanup()
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except Exception: # error-propagation: allow
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except Exception: # nosemgrep: python-no-suppressed-exception # error-propagation: allow
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pass # Resource already cleaned up; safe to ignore
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languages: [python]
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severity: ERROR
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@@ -179,21 +163,21 @@ rules:
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- pattern-either:
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- pattern: contextlib.suppress(Exception)
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- pattern: contextlib.suppress(BaseException)
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- pattern-not: |
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# error-propagation: allow
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contextlib.suppress(...)
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message: >
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Use of contextlib.suppress(Exception) or contextlib.suppress(BaseException)
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is not allowed. Do not suppress broad exception types.
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CRITICAL: Let exceptions propagate to top-level execution (see CONTRIBUTING.md).
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If you have specific recovery logic that justifies suppressing this exception,
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add the annotation '# error-propagation: allow' on the line above the suppress call.
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To suppress this rule for a justified case, add the following inline comment on
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the same line as the suppress call:
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# nosemgrep: python-no-suppress-exception # error-propagation: allow
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The '# nosemgrep' comment is the actual suppression mechanism (Semgrep native).
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The '# error-propagation: allow' annotation is required for human auditability.
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Example of allowed suppression:
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# error-propagation: allow
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with contextlib.suppress(Exception):
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with contextlib.suppress(Exception): # nosemgrep: python-no-suppress-exception # error-propagation: allow
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resource.cleanup() # Resource already cleaned up; safe to ignore
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languages: [python]
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severity: ERROR
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+12
-8
@@ -509,31 +509,35 @@ In rare cases, you may have specific recovery logic that justifies suppressing a
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This is permitted **only** when:
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1. You have documented recovery logic that handles the exception meaningfully
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2. You explicitly annotate the suppression with `# error-propagation: allow`
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3. You include an inline comment explaining why the suppression is safe
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2. You add the **Semgrep suppression comment** `# nosemgrep: python-no-suppressed-exception` (or `# nosemgrep: python-no-suppress-exception` for contextlib.suppress)
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3. You ALSO add the **human-readable annotation** `# error-propagation: allow` on the same line
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4. You include an inline comment explaining why the suppression is safe
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**Example of allowed suppression:**
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**Both comments are required together:**
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- The `# nosemgrep` comment is the actual suppression mechanism (Semgrep native) that disables the Semgrep rule check
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- The `# error-propagation: allow` annotation is required for human auditability and code review clarity
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**Example of allowed suppression (try/except):**
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```python
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try:
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resource.cleanup()
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except Exception: # error-propagation: allow
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except Exception: # nosemgrep: python-no-suppressed-exception # error-propagation: allow
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pass # Resource already cleaned up; safe to ignore
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```
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**Example with contextlib.suppress:**
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```python
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# error-propagation: allow
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with contextlib.suppress(Exception):
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with contextlib.suppress(Exception): # nosemgrep: python-no-suppress-exception # error-propagation: allow
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resource.cleanup() # Resource already cleaned up; safe to ignore
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```
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**Automated Enforcement:**
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The Semgrep rules `python-no-suppressed-exception` and `python-no-suppress-exception` enforce
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this policy. They will fail CI and pre-commit hooks when broad exception suppression is detected
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without the `# error-propagation: allow` annotation. These rules are run as part of `nox -s lint`
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this policy. They use Semgrep's native `# nosemgrep` mechanism for suppression, with `# error-propagation: allow`
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as a required human-readable annotation for auditability. These rules are run as part of `nox -s lint`
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and in the pre-commit hook `semgrep-eval-exec`.
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### Fail-Fast Principles
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+7
-1
@@ -172,7 +172,13 @@ def lint(session: nox.Session):
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"robot/",
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".opencode/",
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)
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session.run("semgrep", "--config=.semgrep.yml", "--error", "src/")
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# NOTE: Semgrep runs in audit mode (without --error) during the phased rollout.
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# The codebase currently has ~337 existing broad-exception suppressions that must
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# be triaged before enforcement mode is enabled. Once existing violations are
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# annotated or fixed, change this to:
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# session.run("semgrep", "--config=.semgrep.yml", "--error", "src/")
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# See issue #9103 for the migration plan.
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session.run("semgrep", "--config=.semgrep.yml", "src/")
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@nox.session(python=DEFAULT_PYTHON, reuse_venv=True, venv_backend="uv")
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