Bug #21758: Prism fails to parse heredoc within %Q literal split by another heredoc

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 4.0.0dev (2025-12-02T16:20:43Z master c06c2203ed) +PRISM [x86_64-linux]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[tompng (tomoya ishida)]

Prism fails to parse this code

<<A; %Q
A
#{<<B}
B

Parse error:

a.rb:4: syntax error found (SyntaxError)
  2 | A
  3 | #{<<B}
> 4 | B
    | ^ unexpected constant, expecting end-of-input

B at line 4 appears twice in lex result:

Prism.lex('<<A; %Q
A
#{<<B}
B
').value
#=> 
[[HEREDOC_START(1,0)-(1,3)("<<A"), 1],
 [HEREDOC_END(2,0)-(3,0)("A\n"), 2],
 [SEMICOLON(1,3)-(1,4)(";"), 1],
 [STRING_BEGIN(1,5)-(2,0)("%Q\n"), 1],
 [EMBEXPR_BEGIN(3,0)-(3,2)("\#{"), 1],
 [HEREDOC_START(3,2)-(3,5)("<<B"), 1],
 [HEREDOC_END(4,0)-(5,0)("B\n"), 2],   # B\n here
 [EMBEXPR_END(3,5)-(3,6)("}"), 2],
 [STRING_END(3,6)-(4,0)("\n"), 2],
 [CONSTANT(4,0)-(4,1)("B"), 2],        # Same B again here
 [NEWLINE(4,1)-(5,0)("\n"), 1],
 [EOF(4,1)-(5,0)("\n"), 1]]