llvm: don't detect +flang multiple times (#49876)

fixes #49831

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

var/spack/repos/builtin/packages/llvm/detection_test.yaml

@@ -68,6 +68,34 @@ paths:
         cxx: ".*/bin/clang[+][+]"
         fortran: ".*/bin/flang"
 
+# flang and flang-new in the same directory
+- layout:
+  - executables:
+    - "bin/clang"
+    - "bin/clang++"
+    script: |
+      echo "clang version 20.1.0-rc1 (https://github.com/llvm/llvm-project af7f483a9d801252247b6c72e3763c1f55c5a506)"
+      echo "Target: x86_64-unknown-linux-gnu"
+      echo "Thread model: posix"
+      echo "InstalledDir: /tmp/clang/LLVM-20.1.0-rc1-Linux-X64/bin"
+  - executables:
+    - "bin/flang"
+    - "bin/flang-new"
+    script: |
+      echo "flang version 20.1.0-rc1 (https://github.com/llvm/llvm-project af7f483a9d801252247b6c72e3763c1f55c5a506)"
+      echo "Target: x86_64-unknown-linux-gnu"
+      echo "Thread model: posix"
+      echo "InstalledDir: /tmp/clang/LLVM-20.1.0-rc1-Linux-X64/bin"
+  platforms: ["darwin", "linux"]
+  results:
+  - spec: 'llvm@20.1.0 +flang+clang~lld~lldb'
+    extra_attributes:
+      compilers:
+        c: ".*/bin/clang"
+        cxx: ".*/bin/clang[+][+]"
+        fortran: ".*/bin/flang"
+
+
 # `~` and other weird characters in the version string
 - layout:
   - executables:

var/spack/repos/builtin/packages/llvm/package.py

@@ -801,7 +801,7 @@ def determine_version(cls, exe):
     def determine_variants(cls, exes, version_str):
         # Do not need to reuse more general logic from CompilerPackage
         # because LLVM has kindly named compilers
-        variants, compilers = ["+clang"], {}
+        variants, compilers = {"+clang"}, {}
         lld_found, lldb_found = False, False
         for exe in sorted(exes, key=len):
             name = os.path.basename(exe)
@@ -809,18 +809,18 @@ def determine_variants(cls, exes, version_str):
                 compilers.setdefault("cxx", exe)
             elif "clang" in name:
                 compilers.setdefault("c", exe)
-            elif "flang" in name:
+            elif "flang" in name and "fortran" not in compilers:
-                variants.append("+flang")
+                variants.add("+flang")
                 compilers.setdefault("fortran", exe)
             elif "ld.lld" in name:
                 lld_found = True
             elif "lldb" in name:
                 lldb_found = True
 
-        variants.append("+lld" if lld_found else "~lld")
+        variants.add("+lld" if lld_found else "~lld")
-        variants.append("+lldb" if lldb_found else "~lldb")
+        variants.add("+lldb" if lldb_found else "~lldb")
 
-        return "".join(variants), {"compilers": compilers}
+        return "".join(sorted(variants)), {"compilers": compilers}
 
     @classmethod
     def validate_detected_spec(cls, spec, extra_attributes):