[bot] Fix Rails/DuplicateAssociation by 6[bot] · Pull Request #217 · 6/nitrocop

6 · 2026-03-26T04:27:08Z

Status: Agent is working on this fix...

Cop: Rails/DuplicateAssociation | Backend: codex / hard | Model: gpt-5.4 (xhigh) | Mode: fix
Code bugs: 1 | Run: https://github.com/6/nitrocop/actions/runs/23577367093

Refs #163

Task prompt (4854 tokens)

Fix Rails/DuplicateAssociation — 77 FP, 0 FN

Instructions

You are fixing ONE cop in nitrocop, a Rust Ruby linter that uses Prism for parsing.

Current state: 114 matches, 77 false positives, 0 false negatives.
Focus on: FP (nitrocop flags code RuboCop does not).

⚠ 114 existing matches must not regress. Validate with check_cop.py before committing.

Workflow

Read the Pre-diagnostic Results and Corpus FP/FN Examples sections below first
Verify with RuboCop first (for FP fixes): before writing any code, confirm RuboCop's
behavior on BOTH the specific FP case AND the general pattern:
```
echo '<specific FP case>' > /tmp/test.rb && rubocop --only Rails/DuplicateAssociation /tmp/test.rb
echo '<general pattern>' > /tmp/test.rb && rubocop --only Rails/DuplicateAssociation /tmp/test.rb
```
If RuboCop flags the general pattern, your fix must be narrow enough to not suppress it.
Add a test case FIRST:
- FN fix: add the missed pattern to tests/fixtures/cops/rails/duplicate_association/offense.rb with ^ annotation
- FP fix: add the false-positive pattern to tests/fixtures/cops/rails/duplicate_association/no_offense.rb
Verify test fails: cargo test --lib -- cop::rails::duplicate_association
Fix src/cop/rails/duplicate_association.rs
Verify test passes: cargo test --lib -- cop::rails::duplicate_association
Validate against corpus (REQUIRED before committing):
```
python3 scripts/check_cop.py Rails/DuplicateAssociation --rerun --clone --sample 15
```
If this reports FP or FN regression, your fix is too broad — narrow it down.
Add a /// doc comment on the cop struct documenting what you found and fixed
Commit only your cop's files

Fixture Format

Mark offenses with ^ markers on the line AFTER the offending source line.
The ^ characters must align with the offending columns. The message format is Rails/DuplicateAssociation: <message text>.
See the Current Fixture sections below for real examples from this cop.

IMPORTANT: This is a config/context issue, NOT a detection bug

Pre-diagnostic shows nitrocop already detects all FP/FN patterns correctly in isolation.
The corpus mismatches are caused by configuration differences in target repos.

Do NOT loop trying to fix detection logic — the detection code is correct.

Instead:

Investigate why the cop doesn't fire (FN) or fires incorrectly (FP) in the target
repo's config context. Common causes:
- Include/Exclude patterns in the cop's config not matching the file path
- The cop being disabled by the target repo's .rubocop.yml
- # rubocop:disable comments in the source file
- File path patterns (e.g., spec files excluded by default)
Look at src/config/ for how config affects this cop
If you can fix the config resolution, do so. Otherwise document your findings as a
/// comment on the cop struct and commit what you have.

If your test passes immediately

If you add a test case and it passes without code changes, the corpus mismatch is
caused by config/context differences, not a detection bug.
Do NOT loop trying to make the test fail. Instead:

Investigate config resolution (Include/Exclude, cop enablement, disable comments)
The fix is likely in src/config/ or the cop's config handling, not detection logic
If you cannot determine the root cause within 5 minutes, document your findings as
a /// comment on the cop struct and commit

CRITICAL: Avoid regressions in the opposite direction

When fixing FPs, your change MUST NOT suppress legitimate detections. When fixing FNs,
your change MUST NOT flag code that RuboCop accepts. A fix that eliminates a few issues
in one direction but introduces hundreds in the other is a catastrophic regression.

Before exempting a category of patterns, verify with RuboCop that the general case
is still an offense:

rubocop --only Rails/DuplicateAssociation /tmp/test.rb

If RuboCop flags the general pattern but not your specific case, the difference is in
a narrow context (e.g., enclosing structure, receiver type, argument count) — your fix
must target that specific context, not the broad category.

Rule of thumb: if your fix adds an early return or continue that skips a whole
node type, operator class, or naming pattern, it's probably too broad. Prefer adding a
condition that matches the SPECIFIC differentiating context.

Rules

Only modify src/cop/rails/duplicate_association.rs and tests/fixtures/cops/rails/duplicate_association/
Run cargo test --lib -- cop::rails::duplicate_association to verify your fix (do NOT run the full test suite)
Run python3 scripts/check_cop.py Rails/DuplicateAssociation --rerun --clone --sample 15 before committing to catch regressions
Do NOT touch unrelated files
Do NOT use git stash

Current Fixture: offense.rb

tests/fixtures/cops/rails/duplicate_association/offense.rb

class User < ApplicationRecord
  has_many :posts
  ^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `posts` is defined multiple times. Don't repeat associations.
  has_many :posts, dependent: :destroy
  ^^^^^^^^ Rails/DuplicateAssociation: Association `posts` is defined multiple times. Don't repeat associations.
end

class Post < ApplicationRecord
  belongs_to :author
  ^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `author` is defined multiple times. Don't repeat associations.
  belongs_to :author, optional: true
  ^^^^^^^^^^ Rails/DuplicateAssociation: Association `author` is defined multiple times. Don't repeat associations.
end

class Company < ApplicationRecord
  has_one :address
  ^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `address` is defined multiple times. Don't repeat associations.
  has_one :address, dependent: :destroy
  ^^^^^^^ Rails/DuplicateAssociation: Association `address` is defined multiple times. Don't repeat associations.
end

# has_and_belongs_to_many duplicates
class Tag < ApplicationRecord
  has_and_belongs_to_many :articles
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `articles` is defined multiple times. Don't repeat associations.
  has_and_belongs_to_many :articles
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `articles` is defined multiple times. Don't repeat associations.
end

# String argument instead of symbol
class Invoice < ApplicationRecord
  has_many 'items'
  ^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `items` is defined multiple times. Don't repeat associations.
  has_many 'items', dependent: :destroy
  ^^^^^^^^ Rails/DuplicateAssociation: Association `items` is defined multiple times. Don't repeat associations.
end

# class_name duplicate detection (has_many, not belongs_to)
class Account < ApplicationRecord
  has_many :foos, class_name: 'Foo'
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `class_name: 'Foo'` is defined multiple times. Don't repeat associations.
  has_many :bars, class_name: 'Foo'
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `class_name: 'Foo'` is defined multiple times. Don't repeat associations.
end

# class_name duplicate detection (has_one)
class Profile < ApplicationRecord
  has_one :baz, class_name: 'Bar'
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `class_name: 'Bar'` is defined multiple times. Don't repeat associations.
  has_one :qux, class_name: 'Bar'
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `class_name: 'Bar'` is defined multiple times. Don't repeat associations.
end

# belongs_to in if/else branches (lorint/brick pattern)
class IfBranchModel < ActiveRecord::Base
  if ActiveRecord.version >= Gem::Version.new('5.0')
    belongs_to :person, optional: true
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `person` is defined multiple times. Don't repeat associations.
  else
    belongs_to :person
    ^^^^^^^^^^^^^^^^^^ Rails/DuplicateAssociation: Association `person` is defined multiple times. Don't repeat associations.
  end
end

Current Fixture: no_offense.rb

tests/fixtures/cops/rails/duplicate_association/no_offense.rb

class User < ApplicationRecord
  has_many :posts, dependent: :destroy
  has_one :profile, dependent: :destroy
  belongs_to :company
end

# Serializer classes should not be flagged
class CollectionSerializer < ActivityPub::Serializer
  has_many :items, key: :items, if: -> { condition_a }
  has_many :items, key: :ordered_items, if: -> { condition_b }
end

# has_and_belongs_to_many without duplicates
class Category < ApplicationRecord
  has_and_belongs_to_many :posts
  has_and_belongs_to_many :tags
end

# belongs_to with same class_name is NOT flagged
class Order < ApplicationRecord
  belongs_to :foos, class_name: 'Foo'
  belongs_to :bars, class_name: 'Foo'
end

# class_name with extra options is NOT flagged
class Report < ApplicationRecord
  has_many :foos, if: :condition, class_name: 'Foo'
  has_many :bars, if: :some_condition, class_name: 'Foo'
  has_one :baz, -> { condition }, class_name: 'Bar'
  has_one :qux, -> { some_condition }, class_name: 'Bar'
end

Key Source Files

Rust implementation: src/cop/rails/duplicate_association.rs
RuboCop Ruby source (ground truth): vendor/rubocop-rails/lib/rubocop/cop/rails/duplicate_association.rb
RuboCop test excerpts: vendor/rubocop-rails/spec/rubocop/cop/rails/duplicate_association_spec.rb

Read these files before making changes.

Start Here

Use the existing corpus data to focus on the most concentrated regressions first.

Helpful local commands:

python3 scripts/investigate_cop.py Rails/DuplicateAssociation --repos-only
python3 scripts/investigate_cop.py Rails/DuplicateAssociation --context
python3 scripts/verify_cop_locations.py Rails/DuplicateAssociation

Top FP repos:

voormedia__rails-erd__7c66258 (38 FP) — example examples/applications/gemcutter/models/user.rb:3
lorint__brick__fa07b7f (26 FP) — example spec/models/northwind_spec.rb:25
gisiahq__gisia__b7f70e0 (4 FP) — example app/models/commit_status.rb:47

Representative FP examples:

databasically__lowdown__d593927: vendor/rails/activerecord/test/models/author.rb:11 — Association class_name: "Post" is defined multiple times. Don't repeat associations.
gisiahq__gisia__b7f70e0: app/models/commit_status.rb:47 — Association ci_stage is defined multiple times. Don't repeat associations.
gisiahq__gisia__b7f70e0: app/models/commit_status.rb:50 — Association needs is defined multiple times. Don't repeat associations.

Pre-diagnostic Results

Diagnosis Summary

Each example was tested by running nitrocop on the extracted source in isolation
with --force-default-config to determine if the issue is a code bug or config issue.
Note: source context is truncated and may not parse perfectly. If a diagnosis
seems wrong (e.g., your test passes immediately for a 'CODE BUG'), treat it as
a config/context issue instead.

FP: 0 confirmed code bug(s), 14 context-dependent
Omitted 1 pre-diagnostic FP example(s) with no source context because diagnosed FP examples were available