[all-commits] [llvm/llvm-project] f86eb5: [flang-rt][NAMELIST] Accept empty scalar assignmen...

[Kareem Ergawy via All-commits]

  Branch: refs/heads/users/ergawy/namelist_empty_scalar_value
  Home:   https://github.com/llvm/llvm-project
  Commit: f86eb5d02df63a7c3593076f5f1bdb3ae1740bfa
      https://github.com/llvm/llvm-project/commit/f86eb5d02df63a7c3593076f5f1bdb3ae1740bfa
  Author: ergawy <kareem.ergawy at gmail.com>
  Date:   2026-07-30 (Thu, 30 Jul 2026)

  Changed paths:
    M flang-rt/include/flang-rt/runtime/namelist.h
    M flang-rt/lib/runtime/namelist.cpp
    A flang-rt/test/Driver/namelist-empty-scalar-logical.f90
    M flang-rt/unittests/Runtime/Namelist.cpp
    M flang/docs/Extensions.md

  Log Message:
  -----------
  [flang-rt][NAMELIST] Accept empty scalar assignments as a language extension

Extend Flang's NAMELIST input to accept an assignment to a scalar item
whose value is omitted, e.g. `l=` in

    &nml l= i_count=7 r_value=2.72/

leaving the item's current value unchanged.  This form is non-standard
(F2023 13.11.3.2 requires a value to follow the `=` for a scalar item)
but is accepted by classic nvfortran and gfortran; users porting code
between compilers have come to rely on it.  `flang/docs/Extensions.md`
is updated to list the new NAMELIST extension alongside the existing
`$`/`&` group-start and mid-value `!`-comment extensions.

Implementation
--------------
Every `EditIntegerInput` / `EditRealInput` / `EditLogicalInput` /
`EditCharacterInput` list-directed arm starts with

    if (IsNamelistNameOrSlash(io)) return false;   // no value

which peeks ahead (via `SavedPosition`, no stream consumption) for a
`<name>=` / `<name>%` / `<name>(` shape or one of the terminators
`/` `&` `$`, letting the reader bail cleanly for empty values and
short-array ends.  The helper's first line is

    if (!listInput || !listInput->namelistGroup()) return false;

`InputNamelist` however called `ResetForNextNamelistItem` with
`useDescriptor->rank() > 0 ? &group : nullptr`, so `namelistGroup_`
stayed null for scalars.  The peek was silently disabled and the
value reader consumed the next name-value pair's name as a bare token,
producing a "Bad character" runtime abort.

Pass `&group` unconditionally to `ResetForNextNamelistItem`.  Today
`IsNamelistNameOrSlash` uses `namelistGroup_` only as a boolean gate
(never as a lookup table), so widening it is a no-op for arrays and
enables the same empty-value / next-name detection for scalars.
`NamelistTests.NanInputAmbiguity` (which motivated the original
pointer form) still passes; three new tests cover the empty-scalar
case, the empty-array case, and an empty scalar surrounded by arrays.


  Commit: 330a9c3c0ee9edcc101f5dc9265dfac9e40e4012
      https://github.com/llvm/llvm-project/commit/330a9c3c0ee9edcc101f5dc9265dfac9e40e4012
  Author: ergawy <kareem.ergawy at gmail.com>
  Date:   2026-07-30 (Thu, 30 Jul 2026)

  Changed paths:
    M flang-rt/lib/runtime/namelist.cpp

  Log Message:
  -----------
  [flang-rt] Reword ResetForNextNamelistItem comment as an extension


  Commit: af7fef717c5fe7931238058ca88dea62fa728342
      https://github.com/llvm/llvm-project/commit/af7fef717c5fe7931238058ca88dea62fa728342
  Author: ergawy <kareem.ergawy at gmail.com>
  Date:   2026-07-30 (Thu, 30 Jul 2026)

  Changed paths:
    M flang-rt/unittests/Runtime/Namelist.cpp

  Log Message:
  -----------
  [flang-rt] Reword NamelistTests comments as an extension


  Commit: 89237db30bd5ec94a78821c8ee735df9f55ab38f
      https://github.com/llvm/llvm-project/commit/89237db30bd5ec94a78821c8ee735df9f55ab38f
  Author: ergawy <kareem.ergawy at gmail.com>
  Date:   2026-07-30 (Thu, 30 Jul 2026)

  Changed paths:
    M flang-rt/test/Driver/namelist-empty-scalar-logical.f90

  Log Message:
  -----------
  [flang-rt] Reword namelist-empty-scalar-logical driver test header as an extension


Compare: https://github.com/llvm/llvm-project/compare/2be863b8ad21...89237db30bd5

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