runtime_deps: improve documentation and consistency.

Library/Homebrew/formula.rb

@@ -1487,12 +1487,23 @@ class Formula
     Requirement.expand(self, &block)
   end
 
+  # Returns a Keg for the opt_prefix or installed_prefix if they exist.
+  # If not, return nil.
+  # @private
+  def opt_or_installed_prefix_keg
+    if optlinked? && opt_prefix.exist?
+      Keg.new(opt_prefix)
+    elsif installed_prefix.directory?
+      Keg.new(installed_prefix)
+    end
+  end
+
   # Returns a list of Dependency objects that are required at runtime.
   # @private
   def runtime_dependencies(read_from_tab: true)
     if read_from_tab &&
        installed_prefix.directory? &&
-       (keg = Keg.new(installed_prefix)) &&
+       (keg = opt_or_installed_prefix_keg) &&
        (tab_deps = keg.runtime_dependencies)
       return tab_deps.map { |d| Dependency.new d["full_name"] }.compact
     end
@@ -1500,6 +1511,8 @@ class Formula
     declared_runtime_dependencies | undeclared_runtime_dependencies
   end
 
+  # Returns a list of Dependency objects that are declared in the formula.
+  # @private
   def declared_runtime_dependencies
     recursive_dependencies do |_, dependency|
       Dependency.prune if dependency.build?
@@ -1507,14 +1520,12 @@ class Formula
     end
   end
 
+  # Returns a list of Dependency objects that are not declared in the formula
+  # but the formula links to.
+  # @private
   def undeclared_runtime_dependencies
-    if optlinked?
-      keg = Keg.new(opt_prefix)
-    elsif prefix.directory?
-      keg = Keg.new(prefix)
-    else
-      return []
-    end
+    keg = opt_or_installed_prefix_keg
+    return [] unless keg
 
     linkage_checker = LinkageChecker.new(keg, self)
     linkage_checker.undeclared_deps.map { |n| Dependency.new(n) }

Library/Homebrew/linkage_checker.rb

@@ -2,6 +2,8 @@ require "keg"
 require "formula"
 
 class LinkageChecker
+  attr_reader :undeclared_deps
+
   def initialize(keg, formula = nil)
     @keg = keg
     @formula = formula || resolve_formula(keg)
@@ -142,7 +144,7 @@ class LinkageChecker
 
     missing_deps = @broken_deps.values.flatten.map { |d| dylib_to_dep(d) }
     unnecessary_deps -= missing_deps
-    
+
     [indirect_deps, undeclared_deps, unnecessary_deps]
   end
 

Library/Homebrew/test/formula_spec.rb

@@ -708,19 +708,18 @@ describe Formula do
       expect(f3.runtime_dependencies.map(&:name)).to eq(["foo/bar/f1", "baz/qux/f2"])
     end
 
-    it "includes non-declared direct dependencies" do
+    it "includes non-declared direct dependencies", :focus do
       formula = Class.new(Testball).new
       dependency = formula("dependency") { url "f-1.0" }
 
       formula.brew { formula.install }
-      keg = Keg.for(formula.prefix)
+      keg = Keg.for(formula.installed_prefix)
       keg.link
 
       linkage_checker = double("linkage checker", undeclared_deps: [dependency.name])
-      allow(LinkageChecker).to receive(:new).with(keg, any_args)
-        .and_return(linkage_checker)
+      allow(LinkageChecker).to receive(:new).and_return(linkage_checker)
 
-      expect(formula.runtime_dependencies).to include an_object_having_attributes(name: dependency.name)
+      expect(formula.runtime_dependencies.map(&:name)).to eq [dependency.name]
     end
   end