fix(crew): only report real template variables in fetch_inputs

[ATOM00blue]

Problem

Crew.fetch_inputs() is meant to return the placeholder names a crew expects so callers know what to pass to kickoff(). It scans task descriptions / expected outputs and agent role/goal/backstory with the regex \{(.+?)}, which matches any content between braces.

That regex does not match what actually gets interpolated. interpolate_only() (the function that performs the substitution) only replaces valid identifiers via \{([A-Za-z_][A-Za-z0-9_\-]*)}. As a result, literal braces that are common in prompts — embedded JSON examples, output schemas, etc. — are reported as required inputs even though they are never substituted.

Example:

agent = Agent(
    role="Researcher",
    goal="Research on {topic}.",
    backstory='Reply as JSON like {"name": "value"}.',
)
task = Task(
    description='Analyze {topic} and return {"result": [1, 2, 3]}.',
    expected_output="Summary of {topic}.",
    agent=agent,
)
crew = Crew(agents=[agent], tasks=[task])

crew.fetch_inputs()
# before: {'topic', '"name": "value"', '"result": [1, 2, 3]'}
# after:  {'topic'}

The bogus entries are not real variables, so any value passed for them via kickoff(inputs=...) is silently ignored, and tools that build UIs/prompts from fetch_inputs() surface placeholders that can never be filled.

Fix

Reuse the canonical template-variable pattern that interpolate_only already uses, so input discovery and input substitution share a single source of truth and cannot drift. The pattern is promoted to a public TEMPLATE_VARIABLE_PATTERN in string_utils and imported by crew.py. The now-unused re import in crew.py is removed.

Testing

• Added test_fetch_inputs_ignores_literal_braces, which fails on main (returns the JSON fragments as inputs) and passes with this change.
• Existing test_fetch_inputs and the task/crew interpolation tests still pass.
• ruff check, ruff format --check, and mypy are clean on the changed files.

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Developed with AI coding assistance; reviewed and submitted by the author.

Per CONTRIBUTING.md, this PR should carry the llm-generated label — I do not have permission to apply labels as an external contributor, so could a maintainer please add it.

Summary by CodeRabbit

• Bug Fixes
  • Fixed template variable detection to correctly ignore literal braces in strings (e.g., JSON objects).

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 65c9ac8e-4ddc-4b8f-8bdd-59ee043ed6f9

📥 Commits

Reviewing files that changed from the base of the PR and between 179c20b and 50ebb88.

📒 Files selected for processing (3)

• lib/crewai/src/crewai/crew.py
• lib/crewai/src/crewai/utilities/string_utils.py
• lib/crewai/tests/test_crew.py

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📝 Walkthrough

Walkthrough

This PR refactors template variable pattern extraction into a shared constant exported from string_utils, enabling both string interpolation and crew input discovery to use the same placeholder-matching rule. Direct re module usage in crew.py is replaced with centralized pattern usage, and a new test validates that placeholder extraction correctly identifies only valid identifier patterns.

Changes

Template Pattern Extraction Consolidation

Layer / File(s)	Summary
Shared template pattern contract lib/crewai/src/crewai/utilities/string_utils.py	TEMPLATE_VARIABLE_PATTERN is introduced as an exported, named constant replacing the internal _VARIABLE_PATTERN, and interpolate_only() is updated to use it for placeholder matching.
Crew input discovery pattern update lib/crewai/src/crewai/crew.py	Crew.fetch_inputs() now extracts template variables via the centralized TEMPLATE_VARIABLE_PATTERN instead of local regex compilation. The re module import is removed, and the import from string_utils is expanded to include the pattern constant.
Fetch inputs placeholder validation test lib/crewai/tests/test_crew.py	New test test_fetch_inputs_ignores_literal_braces() verifies that Crew.fetch_inputs() identifies only valid identifier placeholders while correctly ignoring literal braces and non-identifier patterns.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A pattern shared across the land,
No more duplicates, hand in hand!
From string to crew, one truth they know—
Template variables steal the show! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and accurately summarizes the main change: fixing Crew.fetch_inputs() to report only real template variables, not literal braces.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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[Copilot]

Pull request overview

Aligns Crew.fetch_inputs() with the actual interpolation semantics used by interpolate_only(), so input discovery reports only real template variables (and ignores literal braces common in JSON/schema examples).

Changes:

• Introduced a shared TEMPLATE_VARIABLE_PATTERN regex in string_utils (used by interpolate_only).
• Updated Crew.fetch_inputs() to use TEMPLATE_VARIABLE_PATTERN instead of a broad {...} matcher.
• Added a regression test ensuring literal braces / non-identifier placeholders are not reported as required inputs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
lib/crewai/tests/test_crew.py	Adds a regression test covering literal braces and non-identifier brace content in prompts.
lib/crewai/src/crewai/utilities/string_utils.py	Promotes the interpolation regex to TEMPLATE_VARIABLE_PATTERN and reuses it in interpolate_only.
lib/crewai/src/crewai/crew.py	Makes fetch_inputs() reuse the canonical template-variable pattern and removes the unused re import.

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