[BUGFIX] a-b-c: actually set compiler, improved default (#2051)

* Actually set the compiler to the user provided `--cxx` or the scripts default.
* Have a fallback to `c++` in case `arbor.config()['CXX']` does not exist (typically true for pip installed wheels).
* Verbose mode for `a-b-c`

doc/contrib/coding-style.rst

@@ -14,8 +14,8 @@ run the following commands to apply it:
 
    # Install the formatter if not present
    pip install black
-   # Automatically apply style. If unsure what this does read on.
-   black . scripts/build-catalogue.in
+   # Automatically apply style to a certain file. If unsure what this does read on.
+   black . scripts/arbor/build-catalogue.in
 
 The formatter can also be run with ``--check`` to list offending files and
 ``--diff`` to preview changes. Most editors can `integrate with black

scripts/arbor-build-catalogue

@@ -12,23 +12,47 @@ import re
 
 
 config = A.config()
-prefix = Path(config['prefix'])
+prefix = Path(config["prefix"])
+CXX = Path(config["CXX"])
 if not prefix.exists():
     try:
         # Example <>/lib/python3.10/site-packages/arbor
         altern = Path(A.__path__[0]).parent.parent.parent.parent
-        print(f"Warning: prefix '{prefix}' does not exist, falling back to '{altern}'.", file=sys.stderr)
+        print(
+            f"Warning: prefix '{prefix}' does not exist, falling back to '{altern}'.",
+            file=sys.stderr,
+        )
         prefix = altern
     except:
-        print(f"Error: Neither prefix '{prefix}' nor fallback '{altern}' exist; giving up.", file=sys.stderr)
+        print(
+            f"Error: Neither prefix '{prefix}' nor fallback '{altern}' exist. Please specify the prefix where you keep your Python libraries with --prefix.",
+            file=sys.stderr,
+        )
         exit(-1)
+if not CXX.exists():
+    try:
+        # Example <>/lib/python3.10/site-packages/arbor
+        altern = "c++"
+        print(
+            f"Warning: prefix '{CXX}' does not exist, falling back to '{altern}'.",
+            file=sys.stderr,
+        )
+        CXX = altern
+    except:
+        print(
+            f"Error: Neither prefix '{CXX}' nor fallback '{altern}' exist. Please provide a path to a C++ compiler with --cxx",
+            file=sys.stderr,
+        )
+        exit(-1)
+
 
 def parse_arguments():
     parser = argparse.ArgumentParser(
         description="Generate dynamic catalogue and build it into a shared object.",
         usage="%(prog)s catalogue_name mod_source_dir",
         add_help=False,
-        formatter_class=argparse.ArgumentDefaultsHelpFormatter)
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+    )
 
     parser.add_argument("name", metavar="name", type=str, help="Catalogue name.")
 
@@ -54,9 +78,7 @@ enabled) must be present in the target directory.""",
 
     parser.add_argument("-q", "--quiet", action="store_true", help="Less output.")
 
-    parser.add_argument("--cpu",
-                        default=True,
-                        help="Enable CPU support.")
+    parser.add_argument("--cpu", default=True, help="Enable CPU support.")
 
     parser.add_argument(
         "--debug",
@@ -65,7 +87,7 @@ enabled) must be present in the target directory.""",
         const=True,
         default=None,
         help="Don't clean up the generated temp cpp code."
-            +" Can be a target path for the generated code.",
+        + " Can be a target path for the generated code.",
     )
 
     parser.add_argument(
@@ -79,8 +101,8 @@ enabled) must be present in the target directory.""",
     parser.add_argument(
         "--cxx",
         metavar="cxx",
-        default=config["CXX"],
-        help='Use this C++ compiler.',
+        default=CXX,
+        help="Use this C++ compiler.",
     )
 
     parser.add_argument(
@@ -126,6 +148,12 @@ mod_dir = pwd / Path(args["modpfx"])
 mods = [f[:-4] for f in os.listdir(mod_dir) if f.endswith(".mod")]
 quiet = args["quiet"]
 verbose = args["verbose"] and not quiet
+if verbose:
+    print("=" * 80)
+    print(f"{os.path.basename(__file__)} called with the following arguments:")
+    for k, v in args.items():
+        print(k, v)
+    print("=" * 80)
 debug = args["debug"]
 raw = args["raw"]
 gpu = args["gpu"]
@@ -191,7 +219,7 @@ set(arbor_DIR {pakdir})
 find_package(arbor REQUIRED)
 {gpu_support}
 set(CMAKE_BUILD_TYPE release)
-set(CMAKE_CXX_COMPILER  ${{ARB_CXX}})
+set(CMAKE_CXX_COMPILER  {args["cxx"]})
 set(CMAKE_CXX_FLAGS     ${{ARB_CXX_FLAGS}})
 
 include(BuildModules.cmake)