fix(workflows): quote-aware interpolation so a literal }} in a filter arg doesn't break multi-expression templates (#3307)

* fix(workflows): quote-aware interpolation so a literal }} in a filter arg doesn't break multi-expression templates

#3208/#3228 hardened the single-expression fast path (_is_single_expression)
so a literal {{ or }} inside a string argument like `| default('}}')` stays on
the typed path. the multi-expression interpolation path was left on the old
_EXPR_PATTERN regex, whose non-greedy `(.+?)}}` body stops at the first }}
regardless of quoting. so a multi-expression template with a literal }} in any
block captured a truncated body, hit the filter parser malformed, and raised
ValueError.

e.g. `{{ inputs.name }}: {{ inputs.missing | default('}}') }}` raised instead
of interpolating.

replace _EXPR_PATTERN.sub with _interpolate_expressions, which scans each block
for a }} outside string literals - the same quote handling _is_single_expression
already uses. plain-value passthrough (a literal }} in a resolved value, not an
expression) is unchanged.

add regression tests for a literal }} in the second block and in the first
block, plus a literal {{ guard.

* fix(workflows): surface malformed templates in interpolation instead of emitting verbatim

address copilot review on #3307: when the quote-aware scan finds no block-closing
`}}` (e.g. an unbalanced quote in a filter arg swallowed the delimiter), fall back
to the first raw `}}` in the tail and evaluate it, so the parser raises ValueError
just as the old _EXPR_PATTERN.sub path did. only when there is no `}}` at all is
the tail left verbatim (a genuinely unterminated `{{`, which the regex also could
not match). keeps a typo failing loudly rather than being silently hidden.

add a regression test for an unbalanced quote in a multi-expression template.

Author: Quratulain-bilal

src/specify_cli/workflows/expressions.py

@@ -183,6 +183,65 @@ def _is_single_expression(stripped: str) -> bool:
     return True
 
 
+def _interpolate_expressions(template: str, namespace: dict[str, Any]) -> str:
+    """Substitute every top-level ``{{ ... }}`` block in *template*, quote-aware.
+
+    Walks the template and, for each block, finds the closing ``}}`` that lies
+    outside string literals -- the same quote-scanning used by
+    ``_is_single_expression``. This keeps a literal ``}}`` inside a string
+    argument (e.g. ``| default('}}')``) from prematurely closing a block.
+
+    ``_EXPR_PATTERN.sub`` cannot do this: its non-greedy body stops at the first
+    ``}}`` regardless of quoting, so in a multi-expression template any block
+    whose argument contains a literal ``}}`` is captured truncated and mis-parsed
+    (raising ``ValueError`` from the filter parser). #3208/#3228 fixed exactly
+    this for the single-expression fast path but left the interpolation path on
+    the old regex.
+    """
+    out: list[str] = []
+    i = 0
+    n = len(template)
+    while i < n:
+        start = template.find("{{", i)
+        if start == -1:
+            out.append(template[i:])
+            break
+        out.append(template[i:start])
+        # Scan for the block-closing ``}}`` that is outside any string literal.
+        j = start + 2
+        quote: str | None = None
+        close = -1
+        while j < n:
+            ch = template[j]
+            if quote is not None:
+                if ch == quote:
+                    quote = None
+            elif ch in ("'", '"'):
+                quote = ch
+            elif ch == "}" and j + 1 < n and template[j + 1] == "}":
+                close = j
+                break
+            j += 1
+        if close == -1:
+            # No quote-aware close. Two sub-cases, both kept identical to the old
+            # regex so a malformed template is never silently hidden:
+            #   * a raw ``}}`` still exists in the tail (e.g. an unbalanced quote
+            #     in a filter arg swallowed the real delimiter) -- fall back to
+            #     that first raw ``}}`` and evaluate, letting the parser surface
+            #     a ValueError just as ``_EXPR_PATTERN.sub`` would have.
+            #   * no ``}}`` at all -- a genuinely unterminated ``{{``; leave the
+            #     tail verbatim, again matching the regex (which cannot match).
+            raw_close = template.find("}}", start + 2)
+            if raw_close == -1:
+                out.append(template[start:])
+                break
+            close = raw_close
+        val = _evaluate_simple_expression(template[start + 2:close].strip(), namespace)
+        out.append(str(val) if val is not None else "")
+        i = close + 2
+    return "".join(out)
+
+
 def _split_top_level_commas(text: str) -> list[str]:
     """Split *text* on commas that are not inside quotes or nested brackets.
 
@@ -472,12 +531,11 @@ def evaluate_expression(template: str, context: Any) -> Any:
     if _is_single_expression(stripped):
         return _evaluate_simple_expression(stripped[2:-2].strip(), namespace)
 
-    # Multi-expression: string interpolation
-    def _replacer(m: re.Match[str]) -> str:
-        val = _evaluate_simple_expression(m.group(1).strip(), namespace)
-        return str(val) if val is not None else ""
-
-    return _EXPR_PATTERN.sub(_replacer, template)
+    # Multi-expression: interpolate each block inline. Uses a quote-aware scan
+    # (not ``_EXPR_PATTERN.sub``) so a literal ``}}`` inside a string argument
+    # in any block does not close that block early -- matching the handling the
+    # single-expression path above already got in #3208/#3228.
+    return _interpolate_expressions(template, namespace)
 
 
 def evaluate_condition(condition: str, context: Any) -> bool:

tests/test_workflows.py

@@ -260,6 +260,60 @@ def test_single_expression_with_literal_braces_preserves_type(self):
         ctx = StepContext(inputs={"text": "uses }} syntax"})
         assert evaluate_expression("{{ inputs.text | contains('}}') }}", ctx) is True
 
+    def test_multi_expression_with_literal_close_brace_in_argument(self):
+        """A multi-expression template with a literal ``}}`` inside a string
+        argument must interpolate, not raise. #3208/#3228 hardened the single-
+        expression fast path for literal braces but left the interpolation path
+        on ``_EXPR_PATTERN``, whose non-greedy body stops at the first ``}}`` --
+        so the block was captured truncated and the filter parser raised
+        ValueError."""
+        from specify_cli.workflows.expressions import evaluate_expression
+        from specify_cli.workflows.base import StepContext
+
+        ctx = StepContext(inputs={"name": "Bob", "missing": None})
+        # ``}}`` in the default fallback of the second block.
+        result = evaluate_expression(
+            "{{ inputs.name }}: {{ inputs.missing | default('}}') }}", ctx
+        )
+        assert result == "Bob: }}"
+        # ``}}`` in the first block, expression following it.
+        result = evaluate_expression(
+            "{{ inputs.missing | default('}}') }} / {{ inputs.name }}", ctx
+        )
+        assert result == "}} / Bob"
+
+    def test_multi_expression_with_literal_open_brace_in_argument(self):
+        """A literal ``{{`` inside a string argument in a multi-expression
+        template must not confuse block detection either."""
+        from specify_cli.workflows.expressions import evaluate_expression
+        from specify_cli.workflows.base import StepContext
+
+        ctx = StepContext(inputs={"name": "Bob", "missing": None})
+        result = evaluate_expression(
+            "{{ inputs.name }} {{ inputs.missing | default('{{') }}", ctx
+        )
+        assert result == "Bob {{"
+
+    def test_multi_expression_unbalanced_quote_still_raises(self):
+        """A malformed block (an unbalanced quote in a filter arg) must still
+        surface a ValueError, not be silently emitted verbatim.
+
+        The quote-aware scan never finds a block-closing ``}}`` when a quote is
+        left open, but a raw ``}}`` is still present in the tail. It must fall
+        back to that raw delimiter and evaluate — same as the old regex path —
+        so a typo fails loudly instead of being hidden (Copilot review on
+        #3307)."""
+        import pytest
+
+        from specify_cli.workflows.expressions import evaluate_expression
+        from specify_cli.workflows.base import StepContext
+
+        ctx = StepContext(inputs={"name": "Bob", "missing": None})
+        with pytest.raises(ValueError):
+            evaluate_expression(
+                "{{ inputs.name }} {{ inputs.missing | default('oops }}", ctx
+            )
+
     def test_comparison_equals(self):
         from specify_cli.workflows.expressions import evaluate_expression
         from specify_cli.workflows.base import StepContext