[clang] [flang] [flang] Align `-x` language modes with `gfortran` (PR #130268)

[Iñaki Amatria Barral via cfe-commits]

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@@ -0,0 +1,35 @@
+program main
+  print *, __FILE__, __LINE__
+end
+
+! This test verifies that `flang`'s `-x` options behave like `gfortran`'s.
+! Specifically:
+! - `-x f95` should process the file based on its extension unless overridden.
+! - `-x f95-cpp-input` should behave like `-x f95` but with preprocessing
+!   (`-cpp`) enabled unless overridden.
+
+! ---
+! Ensure the file is treated as fixed-form unless explicitly set otherwise
+! ---
+! RUN: not %flang -Werror -x f95 -cpp %s 2>&1 | FileCheck --check-prefix=SCAN-ERROR %s
+! RUN: not %flang -Werror -x f95-cpp-input %s 2>&1 | FileCheck --check-prefix=SCAN-ERROR %s
+
+! SCAN-ERROR: error
+
+! RUN: %flang -Werror -x f95 -cpp -ffree-form %s 2>&1 | FileCheck --check-prefix=NO-SCAN-ERROR --allow-empty %s
+! RUN: %flang -Werror -x f95-cpp-input -ffree-form %s 2>&1 | FileCheck --check-prefix=NO-SCAN-ERROR --allow-empty %s
+
+! NO-SCAN-ERROR-NOT: error
+
+! ---
+! Ensure `-cpp` is not enabled by default unless explicitly requested
+! ---
+! RUN: not %flang -Werror -x f95 -ffree-form %s 2>&1 | FileCheck --check-prefix=SEMA-ERROR %s
+! RUN: not %flang -Werror -x f95-cpp-input -nocpp -ffree-form %s 2>&1 | FileCheck --check-prefix=SEMA-ERROR %s
+
+! SEMA-ERROR: error
----------------
inaki-amatria wrote:

Fixed. I replaced the `! CHECK: error` pattern with specific checks!

https://github.com/llvm/llvm-project/pull/130268