Line Continuations

⚠️ Experimental: ROUP now understands multi-line OpenMP directives across C, C++, and Fortran. This guide shows how to format continuations so the parser and ompparser compatibility layer recognize them reliably.

When to use continuations

OpenMP pragmas often grow long once multiple clauses are attached. Rather than forcing everything onto a single line, you can split directives while keeping source files readable. ROUP stitches the continued lines together during lexing, so downstream APIs still observe canonical single-line directive strings.

Continuations are supported in two situations:

• C / C++ pragmas that end a line with a trailing backslash (\).
• Fortran sentinels (!$OMP, C$OMP, *$OMP) that use the standard ampersand (&) continuation syntax.

ROUP preserves clause order and trims whitespace that was introduced only to align indentation.

C / C++ example

#pragma omp parallel for \
    schedule(dynamic, 4) \
    private(i, \
            j)

ROUP merges this directive into #pragma omp parallel for schedule(dynamic, 4) private(i, j). Clause arguments keep their original spacing. Comments (/* */ or //) may appear between continued lines and are ignored during merging.

Tips for C / C++

• The backslash must be the final character on the line (aside from trailing spaces or tabs).
• Windows line endings (\r\n) are handled automatically.
• Keep at least one space between the directive name and the first clause on subsequent lines.

Fortran free-form example

!$omp target teams distribute &
!$omp parallel do &
!$omp& private(i, j)

The parser removes the continuation markers and produces !$omp target teams distribute parallel do private(i, j).

Fortran fixed-form example

      C$OMP   DO &
      !$OMP& SCHEDULE(DYNAMIC) &
      !$OMP PRIVATE(I) SHARED(A)

Column prefixes (!, C, or *) are respected. ROUP normalizes the directive to do schedule(DYNAMIC) private(I) shared(A).

Tips for Fortran continuations

• Terminate every continued line with &. ROUP tolerates trailing comments (e.g., & ! explanation) and skips them automatically.
• You may repeat the sentinel on continuation lines (!$OMP&), or start the next line with only &. Both forms are accepted.
• Blank continuation lines are ignored as long as they contain only whitespace.
• Clause bodies can span multiple lines; nested continuations inside parentheses are collapsed to a single line in the parsed clause value.

Troubleshooting

• Missing continuation marker: If a line break appears without & (Fortran) or \ (C/C++), the parser treats the next line as a separate statement and reports an error or unexpected directive name.
• Custom formatting macros: Preprocessors that insert trailing spaces after \ may break continuations. Ensure the backslash is the final printable character.
• Compatibility layer: The ompparser shim mirrors the same behavior. The comprehensive tests in compat/ompparser/tests/comprehensive_test.cpp include multi-line inputs for both languages.

For more examples, refer to the automated tests in tests/openmp_line_continuations.rs and the parser unit tests in src/parser/mod.rs.