fix util/generate_project.py

- fix premake args being incorrect
- remove platform assumptions, making it portable
- start with a best guess based on project layout
- use fallback if not specified or not found
- display errors/help if not found

util/generate_projects.py

@@ -3,26 +3,48 @@
 import sys
 from os import getenv, path
 from subprocess import PIPE, run
+import platform
 
 PREMAKE_DIR = path.join(path.dirname(__file__), "../projects/premake")
 
+# Default binary name
+PREMAKE_BIN = "premake5"
+if platform.system() == "Windows":
+  PREMAKE_BIN += ".exe"
 
-def has(prog):
-    return run(["command", "-v", prog], stdout=PIPE, stderr=PIPE).returncode == 0
-
+# We try the env first, as that's absolute.
+# If not found we try the 'intended' approach,
+# of placing a premake binary alongside premake5.lua.
+# If that isn't found, attempt the plain binary name.
+premake = getenv("WREN_PREMAKE", None)
+if premake is None:
+  premake = PREMAKE_BIN
+  premake_local = path.join(PREMAKE_DIR, PREMAKE_BIN)
+  if path.isfile(premake_local):
+    print("Using local premake in 'projects/premake' ...")
+    premake = premake_local
+else:
+  print("Using premake from 'WREN_PREMAKE' env ...")
 
 def run_premake(action, os):
-    run([premake, action, os], cwd=PREMAKE_DIR)
+  run([premake, action, "--os=" + os], cwd=PREMAKE_DIR)
 
+try:
 
-premake = getenv("PREMAKE", "premake5")
-if not has(premake):
-    print("error: {} is not found", premake, file=sys.stderr)
-    exit(1)
+  run_premake("gmake2", "bsd")
+  run_premake("gmake2", "linux")
+  run_premake("vs2017", "windows")
+  run_premake("vs2019", "windows")
+  run_premake("gmake2", "macosx")
+  run_premake("xcode4", "macosx")
 
-run_premake("gmake2", "bsd")
-run_premake("gmake2", "linux")
-run_premake("gmake2", "macosx")
-run_premake("vs2017", "windows")
-run_premake("vs2019", "windows")
-run_premake("xcode4", "macosx")
+except Exception as e:
+
+  print("Unable to run premake, while trying the binary '" + premake + "' ...")
+  print("  reason: " + str(e))
+  print("\nIf premake can't be found, possible options are:")
+  print("- Set the env variable 'WREN_PREMAKE' to the path to a premake binary")
+  print("- Place a premake5 binary for your host platform in projects/premake")
+  print("- Add a location with a premake5 binary to the PATH")
+
+  exit(1)