compilers/dmd: Determine the backend version for gdmd

This changes makes the compiler version for gdmd match the gdc version
instead of the dmd FE version that gdc had been using. This matches
what happens for ldmd2 which mirrors the ldc2 version.

Specifically, now the versions look like:
- ldmd2-1.40 :: 1.40.X
- ldc2-1.40 :: 1.40.X
- gdc-14 :: 14.X.Y
- gdmd-14 :: 14.X.Y

When, previously, gdmd-14 would result in a version like 2.108.X

Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>

Author: the-horo

source/dub/compilers/compiler.d

@@ -132,7 +132,7 @@ interface Compiler {
 	string[] lflagsToDFlags(const string[] lflags) const;
 
 	/// Determines compiler version
-	string determineVersion(string compiler_binary, string verboseOutput);
+	string determineVersion(in BuildPlatform platform, string verboseOutput);
 
 	/** Runs a tool and provides common boilerplate code.
 
@@ -193,8 +193,8 @@ interface Compiler {
 				format("Failed to invoke the compiler %s to determine the build platform: %s",
 				compiler_binary, result.output));
 		BuildPlatform build_platform = readPlatformSDLProbe(result.output);
-		string ver = determineVersion(compiler_binary, result.output).strip;
 		build_platform.compilerBinary = compiler_binary;
+		string ver = determineVersion(build_platform, result.output).strip;
 
 		if (ver.empty) {
 			logWarn(`Could not probe the compiler version for "%s". ` ~

source/dub/compilers/dmd.d

@@ -99,11 +99,29 @@ config    /etc/dmd.conf
 		assert(c && c.length > 1 && c[1] == "2.084.0-beta.1");
 	}
 
-	string determineVersion(string compiler_binary, string verboseOutput)
+	string determineVersion(in BuildPlatform platform, string verboseOutput)
 	{
-		import std.regex : matchFirst, regex;
-		auto ver = matchFirst(verboseOutput, regex(dmdVersionRe, "m"));
-		return ver && ver.length > 1 ? ver[1] : null;
+		// Find the backend version of the compiler, not the dmd FE.
+		// Specificically, for gdmd-14 this function should return
+		// 14.X.Y not 2.108.Z
+		switch (platform.compiler) {
+		case "dmd":
+		case "ldc":
+			{
+				import std.regex : matchFirst, regex;
+				auto ver = matchFirst(verboseOutput, regex(dmdVersionRe, "m"));
+				return ver && ver.length > 1 ? ver[1] : null;
+			}
+		case "gdc":
+			{
+				import std.process;
+				const result = execute([platform.compilerBinary, "-q,-dumpfullversion", "--version"]);
+				return result.status == 0 ? result.output : null;
+			}
+		default:
+			throw new UnknownCompilerException(platform.compiler);
+		}
+
 	}
 
 	BuildPlatform determinePlatform(ref BuildSettings settings, string compiler_binary, string arch_override)

source/dub/compilers/gdc.d

@@ -54,10 +54,10 @@ class GDCCompiler : Compiler {
 
 	@property string name() const { return "gdc"; }
 
-	string determineVersion(string compiler_binary, string verboseOutput)
+	string determineVersion(in BuildPlatform platform, string verboseOutput)
 	{
 		const result = execute([
-			compiler_binary,
+			platform.compilerBinary,
 			"-dumpfullversion",
 			"-dumpversion"
 		]);

source/dub/compilers/ldc.d

@@ -69,7 +69,7 @@ config    /etc/ldc2.conf (x86_64-pc-linux-gnu)
 		assert(c && c.length > 1 && c[1] == "1.11.0");
 	}
 
-	string determineVersion(string compiler_binary, string verboseOutput)
+	string determineVersion(in BuildPlatform platform, string verboseOutput)
 	{
 		import std.regex : matchFirst, regex;
 		auto ver = matchFirst(verboseOutput, regex(ldcVersionRe, "m"));