add initial support for llvm-flang

6 files changed, 92 insertions, 9 deletions

diff --git a/docs/markdown/Contributing.md b/docs/markdown/Contributing.md
index 731abc87d..8f796ab65 100644
--- a/docs/markdown/Contributing.md
+++ b/docs/markdown/Contributing.md
@@ -150,8 +150,8 @@ Subsets of project tests can be selected with
 time when only a certain part of Meson is being tested.
 For example, a useful and easy contribution to Meson is making
 sure the full set of compilers is supported. One could for example test
-various Fortran compilers by setting `FC=ifort` or `FC=flang` or similar
-with `./run_project_test.py --only fortran`.
+various Fortran compilers by setting `FC=ifort`, `FC=flang` or
+`FC=flang-new` or similar with `./run_project_test.py --only fortran`.
 Some families of tests require a particular backend to run.
 For example, all the CUDA project tests run and pass on Windows via
 `./run_project_tests.py --only cuda --backend ninja`
diff --git a/docs/markdown/Reference-tables.md b/docs/markdown/Reference-tables.md
index 2357ff459..67eccb4a2 100644
--- a/docs/markdown/Reference-tables.md
+++ b/docs/markdown/Reference-tables.md
@@ -15,7 +15,7 @@ These are return values of the `get_id` (Compiler family) and
 | clang-cl  | The Clang compiler (MSVC compatible driver) | msvc |
 | dmd       | D lang reference compiler        |                 |
 | emscripten| Emscripten WASM compiler         |                 |
-| flang     | Flang Fortran compiler           |                 |
+| flang     | Classic Flang Fortran compiler   |                 |
 | g95       | The G95 Fortran compiler         |                 |
 | gcc       | The GNU Compiler Collection      | gcc             |
 | intel     | Intel compiler (Linux and Mac)   | gcc             |
@@ -24,6 +24,7 @@ These are return values of the `get_id` (Compiler family) and
 | intel-llvm-cl | Intel oneAPI LLVM-based compiler (Windows)  | msvc            |
 | lcc       | Elbrus C/C++/Fortran Compiler    |                 |
 | llvm      | LLVM-based compiler (Swift, D)   |                 |
+| llvm-flang| Flang Fortran compiler (LLVM-based) |              |
 | mono      | Xamarin C# compiler              |                 |
 | mwccarm   | Metrowerks C/C++ compiler for Embedded ARM         |                 |
 | mwcceppc  | Metrowerks C/C++ compiler for Embedded PowerPC     |                 |
diff --git a/docs/markdown/snippets/llvm_flang.md b/docs/markdown/snippets/llvm_flang.md
new file mode 100644
index 000000000..4575fe054
--- /dev/null
+++ b/docs/markdown/snippets/llvm_flang.md
@@ -0,0 +1,9 @@
+## Support for LLVM-based flang compiler
+
+Added basic handling for the [flang](https://flang.llvm.org/docs/) compiler
+that's now part of LLVM. It is the successor of another compiler named
+[flang](https://github.com/flang-compiler/flang) by largely the same
+group of developers, who now refer to the latter as "classic flang".
+
+Meson already supports classic flang, and the LLVM-based flang now
+uses the compiler-id `'llvm-flang'`.
diff --git a/mesonbuild/compilers/detect.py b/mesonbuild/compilers/detect.py
index 3a678211c..c796c2f38 100644
--- a/mesonbuild/compilers/detect.py
+++ b/mesonbuild/compilers/detect.py
@@ -45,7 +45,8 @@ if is_windows():
     defaults['c'] = ['icl', 'cl', 'cc', 'gcc', 'clang', 'clang-cl', 'pgcc']
     # There is currently no pgc++ for Windows, only for  Mac and Linux.
     defaults['cpp'] = ['icl', 'cl', 'c++', 'g++', 'clang++', 'clang-cl']
-    defaults['fortran'] = ['ifort', 'gfortran', 'flang', 'pgfortran', 'g95']
+    # the binary flang-new will be renamed to flang in the foreseeable future
+    defaults['fortran'] = ['ifort', 'gfortran', 'flang-new', 'flang', 'pgfortran', 'g95']
     defaults['objc'] = ['clang-cl', 'gcc']
     defaults['objcpp'] = ['clang-cl', 'g++']
     defaults['cs'] = ['csc', 'mcs']
@@ -60,7 +61,8 @@ else:
         defaults['cpp'] = ['c++', 'g++', 'clang++', 'nvc++', 'pgc++', 'icpc', 'icpx']
         defaults['objc'] = ['clang', 'gcc']
         defaults['objcpp'] = ['clang++', 'g++']
-    defaults['fortran'] = ['gfortran', 'flang', 'nvfortran', 'pgfortran', 'ifort', 'ifx', 'g95']
+    # the binary flang-new will be renamed to flang in the foreseeable future
+    defaults['fortran'] = ['gfortran', 'flang-new', 'flang', 'nvfortran', 'pgfortran', 'ifort', 'ifx', 'g95']
     defaults['cs'] = ['mcs', 'csc']
 defaults['d'] = ['ldc2', 'ldc', 'gdc', 'dmd']
 defaults['java'] = ['javac']
@@ -659,6 +661,13 @@ def detect_fortran_compiler(env: 'Environment', for_machine: MachineChoice) -> C
     info = env.machines[for_machine]
     cls: T.Type[FortranCompiler]
     for compiler in compilers:
+        # capture help text for possible fallback
+        try:
+            _, help_out, _ = Popen_safe_logged(compiler + ['--help'], msg='Detecting compiler via')
+        except OSError as e:
+            popen_exceptions[join_args(compiler + ['--help'])] = e
+            help_out = ''
+
         for arg in ['--version', '-V']:
             try:
                 p, out, err = Popen_safe_logged(compiler + [arg], msg='Detecting compiler via')
@@ -776,8 +785,7 @@ def detect_fortran_compiler(env: 'Environment', for_machine: MachineChoice) -> C
                     compiler, version, for_machine, is_cross, info,
                     full_version=full_version, linker=linker)
 
-            if 'flang' in out or 'clang' in out:
-                cls = fortran.FlangFortranCompiler
+            def _get_linker_try_windows(cls: T.Type['Compiler']) -> T.Optional['DynamicLinker']:
                 linker = None
                 if 'windows' in out or env.machines[for_machine].is_windows():
                     # If we're in a MINGW context this actually will use a gnu
@@ -793,6 +801,18 @@ def detect_fortran_compiler(env: 'Environment', for_machine: MachineChoice) -> C
                 if linker is None:
                     linker = guess_nix_linker(env, compiler, cls,
                                               version, for_machine)
+                return linker
+
+            if 'flang-new' in out or 'flang LLVM compiler' in help_out:
+                cls = fortran.LlvmFlangFortranCompiler
+                linker = _get_linker_try_windows(cls)
+                return cls(
+                    compiler, version, for_machine, is_cross, info,
+                    full_version=full_version, linker=linker)
+
+            if 'flang' in out or 'clang' in out:
+                cls = fortran.ClassicFlangFortranCompiler
+                linker = _get_linker_try_windows(cls)
                 return cls(
                     compiler, version, for_machine, is_cross, info,
                     full_version=full_version, linker=linker)
diff --git a/mesonbuild/compilers/fortran.py b/mesonbuild/compilers/fortran.py
index a6e3f0b21..a99a95ce3 100644
--- a/mesonbuild/compilers/fortran.py
+++ b/mesonbuild/compilers/fortran.py
@@ -430,7 +430,7 @@ class NvidiaHPC_FortranCompiler(PGICompiler, FortranCompiler):
                           'everything': default_warn_args + ['-Mdclchk']}
 
 
-class FlangFortranCompiler(ClangCompiler, FortranCompiler):
+class ClassicFlangFortranCompiler(ClangCompiler, FortranCompiler):
 
     id = 'flang'
 
@@ -460,10 +460,62 @@ class FlangFortranCompiler(ClangCompiler, FortranCompiler):
             search_dirs.append(f'-L{d}')
         return search_dirs + ['-lflang', '-lpgmath']
 
-class ArmLtdFlangFortranCompiler(FlangFortranCompiler):
+
+class ArmLtdFlangFortranCompiler(ClassicFlangFortranCompiler):
 
     id = 'armltdflang'
 
+
+class LlvmFlangFortranCompiler(ClangCompiler, FortranCompiler):
+
+    id = 'llvm-flang'
+
+    def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
+                 info: 'MachineInfo', linker: T.Optional['DynamicLinker'] = None,
+                 full_version: T.Optional[str] = None):
+        FortranCompiler.__init__(self, exelist, version, for_machine,
+                                 is_cross, info, linker=linker,
+                                 full_version=full_version)
+        ClangCompiler.__init__(self, {})
+        default_warn_args = ['-Wall']
+        self.warn_args = {'0': [],
+                          '1': default_warn_args,
+                          '2': default_warn_args,
+                          '3': default_warn_args,
+                          'everything': default_warn_args}
+
+    def get_colorout_args(self, colortype: str) -> T.List[str]:
+        # not yet supported, see https://github.com/llvm/llvm-project/issues/89888
+        return []
+
+    def get_dependency_gen_args(self, outtarget: str, outfile: str) -> T.List[str]:
+        # not yet supported, see https://github.com/llvm/llvm-project/issues/89888
+        return []
+
+    def get_module_outdir_args(self, path: str) -> T.List[str]:
+        # different syntax from classic flang (which supported `-module`), see
+        # https://github.com/llvm/llvm-project/issues/66969
+        return ['-module-dir', path]
+
+    def gnu_symbol_visibility_args(self, vistype: str) -> T.List[str]:
+        # flang doesn't support symbol visibility flag yet, see
+        # https://github.com/llvm/llvm-project/issues/92459
+        return []
+
+    def language_stdlib_only_link_flags(self, env: 'Environment') -> T.List[str]:
+        # matching setup from ClassicFlangFortranCompiler
+        search_dirs: T.List[str] = []
+        for d in self.get_compiler_dirs(env, 'libraries'):
+            search_dirs.append(f'-L{d}')
+        # does not automatically link to Fortran_main anymore after
+        # https://github.com/llvm/llvm-project/commit/9d6837d595719904720e5ff68ec1f1a2665bdc2f
+        # note that this changed again in flang 19 with
+        # https://github.com/llvm/llvm-project/commit/8d5386669ed63548daf1bee415596582d6d78d7d;
+        # it seems flang 18 doesn't work if something accidentally includes a program unit, see
+        # https://github.com/llvm/llvm-project/issues/92496
+        return search_dirs + ['-lFortranRuntime', '-lFortranDecimal']
+
+
 class Open64FortranCompiler(FortranCompiler):
 
     id = 'open64'
diff --git a/run_project_tests.py b/run_project_tests.py
index 7551c8da9..fe1f46f7e 100755
--- a/run_project_tests.py
+++ b/run_project_tests.py
@@ -1086,6 +1086,7 @@ def detect_tests_to_run(only: T.Dict[str, T.List[str]], use_tmp: bool) -> T.List
     """
 
     skip_fortran = not(shutil.which('gfortran') or
+                       shutil.which('flang-new') or
                        shutil.which('flang') or
                        shutil.which('pgfortran') or
                        shutil.which('nagfor') or