Fix issue dlang#2190 - windows: dub won't run if TEMP is unset or empty

source/dub/commandline.d

@@ -371,6 +371,8 @@ unittest {
 */
 int runDubCommandLine(string[] args)
 {
+	import std.file : tempDir;
+
 	static string[] toSinglePackageArgs (string args0, string file, string[] trailing)
 	{
 		return [args0, "run", "-q", "--temp-build", "--single", file, "--"] ~ trailing;
@@ -382,11 +384,24 @@ int runDubCommandLine(string[] args)
 
 	logDiagnostic("DUB version %s", getDUBVersion());
 
-	version(Windows){
-		// rdmd uses $TEMP to compute a temporary path. since cygwin substitutes backslashes
-		// with slashes, this causes OPTLINK to fail (it thinks path segments are options)
-		// we substitute the other way around here to fix this.
-		environment["TEMP"] = environment["TEMP"].replace("/", "\\");
+	{
+		version(Windows) {
+			// Guarantee that this environment variable is set
+			//  this is specifically needed because of the Windows fix that follows this statement.
+			// While it probably isn't needed for all targets, it does simplify things a bit.
+			// Question is can it be more generic? Probably not due to $TMP
+			if ("TEMP" !in environment)
+				environment["TEMP"] = tempDir();
+
+			// rdmd uses $TEMP to compute a temporary path. since cygwin substitutes backslashes
+			// with slashes, this causes OPTLINK to fail (it thinks path segments are options)
+			// we substitute the other way around here to fix this.
+
+			// In case the environment variable TEMP is empty (it should never be), we'll swap out
+			//  opIndex in favor of get with the fallback.
+
+			environment["TEMP"] = environment.get("TEMP", null).replace("/", "\\");
+		}
 	}
 
 	auto handler = CommandLineHandler(getCommands());

test/issue2190-unset-TEMP.script.d

@@ -0,0 +1,51 @@
+/+ dub.json: {
+   "name": "issue2190_unset_TEMP"
+} +/
+
+module issue2190_unset_TEMP.script;
+
+int main()
+{
+	import std.stdio;
+	import std.algorithm;
+	import std.path;
+	import std.process;
+
+	const dir = __FILE_FULL_PATH__.dirName();
+
+	// doesn't matter, just pick something
+	const file = buildPath(dir, "single-file-sdl-default-name.d");
+
+	const dub = environment.get("DUB", buildPath(dirName(dir), "bin", "dub.exe"));
+
+	int exitCode;
+
+	void runTest(scope const string[] cmd)
+	{
+		const result = execute(cmd);
+
+		if (result.status || result.output.canFind("Failed"))
+		{
+			writefln("\n> %-(%s %)", cmd);
+			writeln("===========================================================");
+			writeln(result.output);
+			writeln("===========================================================");
+			writeln("Last command failed with exit code ", result.status, '\n');
+			exitCode = 1;
+		}
+	}
+
+	environment.remove("TEMP");
+
+	// only guaranteed to be there on Windows
+	// See: runDubCommandLine in commandline
+	version(Windows)
+	{
+		runTest([
+			dub, "build",
+			"--single", file,
+		]);
+	}
+
+	return exitCode;
+}