Mark strings returned by Symbol#to_s as chilled (#12065)

* Use FL_USER0 for ELTS_SHARED

This makes space in RString for two bits for chilled strings.

* Mark strings returned by `Symbol#to_s` as chilled

[Feature #20350]

`STR_CHILLED` now spans on two user flags. If one bit is set it
marks a chilled string literal, if it's the other it marks a
`Symbol#to_s` chilled string.

Since it's not possible, and doesn't make much sense to include
debug info when `--debug-frozen-string-literal` is set, we can't
include allocation source, but we can safely include the symbol
name in the warning message, making it much easier to find the source
of the issue.

Co-Authored-By: Étienne Barrié <etienne.barrie@gmail.com>

---------

Co-authored-by: Étienne Barrié <etienne.barrie@gmail.com>
Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

1 files changed, 119 insertions, 47 deletions

diff --git a/spec/ruby/core/string/chilled_string_spec.rb b/spec/ruby/core/string/chilled_string_spec.rb
index 9f81b1af6d..b8fb6eedc9 100644
--- a/spec/ruby/core/string/chilled_string_spec.rb
+++ b/spec/ruby/core/string/chilled_string_spec.rb
@@ -2,69 +2,141 @@ require_relative '../../spec_helper'
 
 describe "chilled String" do
   guard -> { ruby_version_is "3.4" and !"test".equal?("test") } do
-    describe "#frozen?" do
-      it "returns false" do
-        "chilled".frozen?.should == false
+    describe "chilled string literals" do
+
+      describe "#frozen?" do
+        it "returns false" do
+          "chilled".frozen?.should == false
+        end
       end
-    end
 
-    describe "#-@" do
-      it "returns a different instance" do
-        input = "chilled"
-        interned = (-input)
-        interned.frozen?.should == true
-        interned.object_id.should_not == input.object_id
+      describe "#-@" do
+        it "returns a different instance" do
+          input = "chilled"
+          interned = (-input)
+          interned.frozen?.should == true
+          interned.object_id.should_not == input.object_id
+        end
       end
-    end
 
-    describe "#+@" do
-      it "returns a different instance" do
-        input = "chilled"
-        duped = (+input)
-        duped.frozen?.should == false
-        duped.object_id.should_not == input.object_id
+      describe "#+@" do
+        it "returns a different instance" do
+          input = "chilled"
+          duped = (+input)
+          duped.frozen?.should == false
+          duped.object_id.should_not == input.object_id
+        end
       end
-    end
 
-    describe "#clone" do
-      it "preserves chilled status" do
-        input = "chilled".clone
-        -> {
-          input << "-mutated"
-        }.should complain(/literal string will be frozen in the future/)
-        input.should == "chilled-mutated"
+      describe "#clone" do
+        it "preserves chilled status" do
+          input = "chilled".clone
+          -> {
+            input << "-mutated"
+          }.should complain(/literal string will be frozen in the future/)
+          input.should == "chilled-mutated"
+        end
+      end
+
+      describe "mutation" do
+        it "emits a warning" do
+          input = "chilled"
+          -> {
+            input << "-mutated"
+          }.should complain(/literal string will be frozen in the future/)
+          input.should == "chilled-mutated"
+        end
+
+        it "emits a warning on singleton_class creation" do
+          -> {
+            "chilled".singleton_class
+          }.should complain(/literal string will be frozen in the future/)
+        end
+
+        it "emits a warning on instance variable assignment" do
+          -> {
+            "chilled".instance_variable_set(:@ivar, 42)
+          }.should complain(/literal string will be frozen in the future/)
+        end
+
+        it "raises FrozenError after the string was explicitly frozen" do
+          input = "chilled"
+          input.freeze
+          -> {
+            -> {
+            input << "mutated"
+            }.should raise_error(FrozenError)
+          }.should_not complain(/literal string will be frozen in the future/)
+        end
       end
     end
 
-    describe "mutation" do
-      it "emits a warning" do
-        input = "chilled"
-        -> {
-          input << "-mutated"
-        }.should complain(/literal string will be frozen in the future/)
-        input.should == "chilled-mutated"
+    describe "chilled strings returned by Symbol#to_s" do
+
+      describe "#frozen?" do
+        it "returns false" do
+          :chilled.to_s.frozen?.should == false
+        end
       end
 
-      it "emits a warning on singleton_class creation" do
-        -> {
-          "chilled".singleton_class
-        }.should complain(/literal string will be frozen in the future/)
+      describe "#-@" do
+        it "returns a different instance" do
+          input = :chilled.to_s
+          interned = (-input)
+          interned.frozen?.should == true
+          interned.object_id.should_not == input.object_id
+        end
       end
 
-      it "emits a warning on instance variable assignment" do
-        -> {
-          "chilled".instance_variable_set(:@ivar, 42)
-        }.should complain(/literal string will be frozen in the future/)
+      describe "#+@" do
+        it "returns a different instance" do
+          input = :chilled.to_s
+          duped = (+input)
+          duped.frozen?.should == false
+          duped.object_id.should_not == input.object_id
+        end
+      end
+
+      describe "#clone" do
+        it "preserves chilled status" do
+          input = :chilled.to_s.clone
+          -> {
+            input << "-mutated"
+          }.should complain(/string returned by :chilled\.to_s will be frozen in the future/)
+          input.should == "chilled-mutated"
+        end
       end
 
-      it "raises FrozenError after the string was explicitly frozen" do
-        input = "chilled"
-        input.freeze
-        -> {
+      describe "mutation" do
+        it "emits a warning" do
+          input = :chilled.to_s
+          -> {
+            input << "-mutated"
+          }.should complain(/string returned by :chilled\.to_s will be frozen in the future/)
+          input.should == "chilled-mutated"
+        end
+
+        it "emits a warning on singleton_class creation" do
+          -> {
+            :chilled.to_s.singleton_class
+          }.should complain(/string returned by :chilled\.to_s will be frozen in the future/)
+        end
+
+        it "emits a warning on instance variable assignment" do
+          -> {
+            :chilled.to_s.instance_variable_set(:@ivar, 42)
+          }.should complain(/string returned by :chilled\.to_s will be frozen in the future/)
+        end
+
+        it "raises FrozenError after the string was explicitly frozen" do
+          input = :chilled.to_s
+          input.freeze
           -> {
-          input << "mutated"
-          }.should raise_error(FrozenError)
-        }.should_not complain(/literal string will be frozen in the future/)
+            -> {
+            input << "mutated"
+            }.should raise_error(FrozenError)
+          }.should_not complain(/string returned by :chilled\.to_s will be frozen in the future/)
+        end
       end
     end
   end