Interpolated strings must not be frozen

Strings concatenated with backslash may end up being frozen when they
shouldn't be.  This commit fixes the issue.  It required a change
upstream in Prism, but also a change to the Prism compiler in CRuby.

  ruby/prism#3606

[Bug #21187]

Author: tenderlove

prism_compile.c

@@ -557,7 +557,7 @@ parse_regexp_concat(rb_iseq_t *iseq, const pm_scope_node_t *scope_node, const pm
 static void pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret, bool popped, pm_scope_node_t *scope_node);
 
 static int
-pm_interpolated_node_compile(rb_iseq_t *iseq, const pm_node_list_t *parts, const pm_node_location_t *node_location, LINK_ANCHOR *const ret, bool popped, pm_scope_node_t *scope_node, rb_encoding *implicit_regexp_encoding, rb_encoding *explicit_regexp_encoding)
+pm_interpolated_node_compile(rb_iseq_t *iseq, const pm_node_list_t *parts, const pm_node_location_t *node_location, LINK_ANCHOR *const ret, bool popped, pm_scope_node_t *scope_node, rb_encoding *implicit_regexp_encoding, rb_encoding *explicit_regexp_encoding, bool mutable_result)
 {
     int stack_size = 0;
     size_t parts_size = parts->size;
@@ -667,7 +667,7 @@ pm_interpolated_node_compile(rb_iseq_t *iseq, const pm_node_list_t *parts, const
         if (RTEST(current_string)) {
             current_string = rb_fstring(current_string);
 
-            if (stack_size == 0 && interpolated) {
+            if (stack_size == 0 && (interpolated || mutable_result)) {
                 PUSH_INSN1(ret, current_location, putstring, current_string);
             }
             else {
@@ -691,7 +691,7 @@ pm_compile_regexp_dynamic(rb_iseq_t *iseq, const pm_node_t *node, const pm_node_
     rb_encoding *explicit_regexp_encoding = parse_regexp_encoding(scope_node, node);
     rb_encoding *implicit_regexp_encoding = explicit_regexp_encoding != NULL ? explicit_regexp_encoding : scope_node->encoding;
 
-    int length = pm_interpolated_node_compile(iseq, parts, node_location, ret, popped, scope_node, implicit_regexp_encoding, explicit_regexp_encoding);
+    int length = pm_interpolated_node_compile(iseq, parts, node_location, ret, popped, scope_node, implicit_regexp_encoding, explicit_regexp_encoding, false);
     PUSH_INSN2(ret, *node_location, toregexp, INT2FIX(parse_regexp_flags(node) & 0xFF), INT2FIX(length));
 }
 
@@ -9575,7 +9575,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
         }
         else {
             const pm_interpolated_string_node_t *cast = (const pm_interpolated_string_node_t *) node;
-            int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, popped, scope_node, NULL, NULL);
+            int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, popped, scope_node, NULL, NULL, !PM_NODE_FLAG_P(cast, PM_INTERPOLATED_STRING_NODE_FLAGS_FROZEN));
             if (length > 1) PUSH_INSN1(ret, location, concatstrings, INT2FIX(length));
             if (popped) PUSH_INSN(ret, location, pop);
         }
@@ -9586,7 +9586,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
         // :"foo #{bar}"
         // ^^^^^^^^^^^^^
         const pm_interpolated_symbol_node_t *cast = (const pm_interpolated_symbol_node_t *) node;
-        int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, popped, scope_node, NULL, NULL);
+        int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, popped, scope_node, NULL, NULL, false);
 
         if (length > 1) {
             PUSH_INSN1(ret, location, concatstrings, INT2FIX(length));
@@ -9608,7 +9608,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
 
         PUSH_INSN(ret, location, putself);
 
-        int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, false, scope_node, NULL, NULL);
+        int length = pm_interpolated_node_compile(iseq, &cast->parts, &location, ret, false, scope_node, NULL, NULL, false);
         if (length > 1) PUSH_INSN1(ret, location, concatstrings, INT2FIX(length));
 
         PUSH_SEND_WITH_FLAG(ret, location, idBackquote, INT2NUM(1), INT2FIX(VM_CALL_FCALL | VM_CALL_ARGS_SIMPLE));

test/prism/result/static_literals_test.rb

@@ -4,6 +4,11 @@
 
 module Prism
   class StaticLiteralsTest < TestCase
+    def test_concatenanted_string_literal_is_not_static
+      node = Prism.parse_statement("'a' 'b'")
+      refute_predicate node, :static_literal?
+    end
+
     def test_static_literals
       assert_warning("1")
       assert_warning("0xA", "10", "10")