fix(parser): honor backslash-newline line continuations in here-documents

brush-parser/src/word.rs

@@ -872,14 +872,21 @@ peg::parser! {
             legacy_arithmetic_expansion() /
             command_substitution() /
             parameter_expansion() /
+            heredoc_line_continuation() /
             heredoc_escape_sequence() /
             heredoc_literal_text()
 
+        // In a here-document whose delimiter is unquoted, a backslash-newline pair is a
+        // line continuation: it is removed outright, joining the two lines. (A delimiter
+        // that *is* quoted suppresses expansion altogether, so this rule never sees it.)
+        rule heredoc_line_continuation() -> WordPiece =
+            "\\\n" { WordPiece::Text(String::new()) }
+
         rule heredoc_escape_sequence() -> WordPiece =
             s:$("\\" ['$' | '`' | '\\']) { WordPiece::EscapeSequence(s.to_owned()) }
 
         rule heredoc_literal_text() -> WordPiece =
-            s:$((!heredoc_escape_sequence() !dollar_sign_word_piece() [^'`'])+) {
+            s:$((!heredoc_line_continuation() !heredoc_escape_sequence() !dollar_sign_word_piece() [^'`'])+) {
                 WordPiece::Text(s.to_owned())
             }
 

brush-shell/tests/cases/compat/here.yaml

@@ -306,4 +306,38 @@ cases:
         i=$((i + 1))
       done
       out=$(cat <<<"$payload")
-      echo "${#out}"
+      echo "${#out}"
+
+  - name: "Here doc with line continuation"
+    stdin: |
+      cat <<EOF
+      alpha \
+      beta
+      EOF
+
+  - name: "Here doc with line continuation and quoted tag"
+    stdin: |
+      cat <<'EOF'
+      alpha \
+      beta
+      EOF
+
+  - name: "Here doc with line continuation before expansion"
+    stdin: |
+      v=world
+      cat <<EOF
+      hello \
+      $v
+      EOF
+
+  - name: "Here doc escapes alongside line continuation"
+    stdin: |
+      v=world
+      cat <<EOF
+      plain $v
+      dollar \$v
+      backslash \\ end
+      backtick \` end
+      cont \
+      joined
+      EOF