Rails 4.0 patterns: validation anchors + accepts_nested_attributes_for

[JuanVqz]

Summary

Three new Rails 4.0 detection patterns. All three break boot when the model class loads, and the current skill does not catch them.

• VALIDATES_FORMAT_OF_ANCHORS — Rails 4 raises ArgumentError: The provided regular expression is using multiline anchors (^ or $)... when a validates_format_of regex starts with ^ or ends with $. This check is new in 4.0 (Rails 3.2 does not have it), checked against format.rb at v3.2.22.5 vs v4.0.0. Fix is \A / \z, works on both versions, no gate. The regex now matches both anchors ([\^$]), so trailing-$-only forms like with: /foo$/ are caught. Only a leading ^ or trailing $ actually raises, so a ^ inside a character class (/[^@]+/) is a false positive — noted in the entry. Block-options and method-call forms are not caught by the main regex; a second grep is given for them.
• VALIDATES_FORMAT_OF_ANCHORS_CONSTANT_BOUND — catches regex constants built with Regexp.new(%q{^...$}) that feed validators, which the inline grep misses. The regex no longer stops at the first ), so grouped patterns like Regexp.new("(a|b)$") are caught. Check each hit by hand — not every Regexp.new constant feeds a validator, and only a leading ^ or trailing $ raises.
• ACCEPTS_NESTED_NO_REFLECTION — accepts_nested_attributes_for :foo raises ArgumentError: No association found for name 'foo' at class-load when :foo has no association. This raise is not new in Rails 4.0 (it fires on any version when the association is missing), so a missing association is not a 3.2 → 4.0 regression. It shows up as a new failure on the next side only when the association comes from a gem's base class through inheritance, and a gem bump in Gemfile.next removes it. Example: paper_trail 2.x has a top-level Version (with belongs_to :item); 3.x renames it to PaperTrail::Version and drops the top-level Version, so models written as < Version lose the inherited association on the next side only. A hit is only a problem when the association is inherited from a gem's base class and that gem is being bumped in Gemfile.next. Two fixes given: re-point the base class on the next side in one place (Version = PaperTrail::Version if NextRails.next?), or add the association per model (belongs_to ... if NextRails.next?, gated so the current side does not get a duplicate reader/writer). A hand-written def foo override still wins either way.

All three classified high_priority / kind: breaking.

Test plan

• bin/validate-patterns rails-upgrade/detection-scripts/patterns/rails-40-patterns.yml clean.
• Reviewer spot-checks the three regexes against representative 3.x code (literal validates_format_of, Regexp.new constants, accepts_nested_attributes_for macros).