feat: add C3 linearization printer for inheritance analysis

[ep0chzer0]

Summary

Fixes #2784

Adds a new printer that displays the C3 linearization order for contract inheritance, helping developers understand:

• Method resolution order (MRO) - Which implementation is called
• Constructor execution order - Important for proper initialization
• Super call resolution - Which parent implementation super refers to

Features

• Shows linearization order with contract type labels (SELF/BASE/INHERITED)
• Displays source file locations for each contract
• Shows constructor presence (✓/✗) for each contract
• Lists constructor execution order (reverse of linearization)
• Outputs both human-readable format and structured JSON

Example Output

C3 Linearization for D
======================================
  0. [SELF]       D (diamond.sol:42)  [constructor: ✓]
  1. [BASE]       C (diamond.sol:32)  [constructor: ✓]
  2. [BASE]       B (diamond.sol:21)  [constructor: ✓]
  3. [INHERITED]  A (diamond.sol:7)   [constructor: ✓]

  Constructor Execution Order:
    1. A.constructor()
    2. B.constructor()
    3. C.constructor()
    4. D.constructor()

Usage

slither . --print c3-linearization

Test Plan

• Added test with diamond inheritance pattern (A <- B, A <- C, B,C <- D)
• Verifies linearization order matches expected C3 algorithm output
• Verifies constructor execution order is reverse of linearization

[dguido]

Code Review: C3 Linearization Printer

Reviewing: PR #2917 - feat: add C3 linearization printer for inheritance analysis

Summary

This PR adds a useful C3 linearization printer that addresses the core requirements of issue #2784. The implementation is clean and follows existing printer patterns well. A few issues worth addressing:

---

Critical Issues (Confidence: 90+)

1. WIKI URL uses trailofbits instead of crytic (Confidence: 92)

File: slither/printers/inheritance/c3_linearization.py, line 17

The codebase is migrating WIKI URLs from trailofbits/slither to crytic/slither. The existing inheritance.py uses trailofbits, but the newer constructor_calls.py uses crytic. For consistency with the current repository ownership, consider:

# Current:
WIKI = "https://github.com/trailofbits/slither/wiki/Printer-documentation#c3-linearization"

# Suggested:
WIKI = "https://github.com/crytic/slither/wiki/Printer-documentation#c3-linearization"

2. Potential IndexError when source_mapping.lines is empty (Confidence: 85)

File: slither/printers/inheritance/c3_linearization.py, line 56

The code accesses c.source_mapping.lines[0] without checking if lines is non-empty. While rare, lines can be an empty list:

# Current:
if c.source_mapping:
    source_loc = f" ({c.source_mapping.filename.short}:{c.source_mapping.lines[0]})"

# Suggested:
if c.source_mapping and c.source_mapping.lines:
    source_loc = f" ({c.source_mapping.filename.short}:{c.source_mapping.lines[0]})"

---

Important Issues (Confidence: 80-89)

3. Lambda used for identity function (Confidence: 82)

File: slither/printers/inheritance/c3_linearization.py, line 52

Using a lambda for an identity function is functional but could be cleaner:

# Current:
color_fn = lambda x: x  # no color for inherited

# Suggested (avoid lambda assignment per PEP 8):
def identity(x):
    return x
color_fn = identity
# Or simply inline the logic to avoid the function call

---

Suggestions (Not blocking)

1. Consider adding start_line to JSON output - The JSON includes source filename but not the line number, which could be useful for tooling.

2. Test coverage - The test verifies the diamond pattern well. Consider adding a test case for contracts without constructors to ensure the empty constructor handling works correctly.

3. Issue #2784 scope - The issue requested several advanced features (verbose mode, conflict detection, super resolution). This PR implements the core functionality, which is a reasonable first step. Those could be follow-up enhancements.

---

Positive Observations

• Clean implementation following existing printer patterns
• Good use of contract.is_interface to skip interfaces (per CLAUDE.md guidance)
• JSON output structure is well-designed
• Test case covers the classic diamond inheritance pattern
• Constructor execution order display is a nice touch

Overall, this is a solid contribution. The two issues above (WIKI URL and potential IndexError) should be addressed before merging.

[dguido]

PR Review Summary

Research Findings

PR Purpose: This PR adds a new C3 linearization printer (c3-linearization) that displays the method resolution order (MRO) for contract inheritance, addressing issue #2784. The printer shows:

• Linearization order with contract type labels (SELF/BASE/INHERITED)
• Source file locations for each contract
• Constructor presence indicators
• Constructor execution order (reverse of linearization)

The implementation correctly leverages contract.inheritance which already contains the C3 linearized order in Slither.

Test Status

All printer tests pass after merging master:

• test_c3_linearization_printer PASSED
• test_inheritance_graph_printer PASSED
• test_slithir_printer PASSED
• test_inheritance_text_printer PASSED

The failing unit tests (Vyper-related) are pre-existing and unrelated to this PR - they fail due to missing Vyper installation in the test environment.

Code Review Issues Found and Fixed

All issues from the initial review by @dguido have been addressed:

1. WIKI URL (line 18): Changed from trailofbits to crytic to match current repository ownership.

2. Potential IndexError (line 56-57): Added guard for empty source_mapping.lines list.

3. Lambda assignment (line 55): Removed PEP 8 violation by inlining the color logic directly.

4. Additional improvements made:

   • Added type hints to match AbstractPrinter.output() signature
   • Replaced unicode checkmark/x with ASCII +/- for cross-platform compatibility
   • Removed unused variable ctor in constructor iteration
   • Simplified docstring format

Merge Readiness

Ready to merge after the author applies these changes. The implementation is solid and follows existing printer patterns well. The test coverage is appropriate for a new printer.

The suggested fixes have been prepared and tested locally - I can provide a patch or diff if helpful.