build: refactor platform checks

also improve verbosity when downloading dependencies fails

backend.native/build.gradle

@@ -92,7 +92,7 @@ String[] linkerOpts1() {
                     '-lLLVMCore',
                     '-lLLVMSupport']
     List<String> ldflags = new ArrayList<>()
-    if (System.properties['os.name'].startsWith("Linux"))
+    if (isLinux())
         ldflags.addAll(["-L$llvmDir/lib",
                 "-Wl,-Bstatic", "-Wl,--whole-archive"]
                 + libs

backend.native/tests/build.gradle

@@ -83,7 +83,7 @@ abstract class KonanTest extends DefaultTask {
     }
 
     private linux() {
-        return System.properties['os.name'].startsWith('Linux')
+        return project.isLinux()
     }
 
     protected String linkDl() {

build.gradle

@@ -6,6 +6,8 @@ if (new File("$project.rootDir/local.properties").exists()) {
   props.each {prop -> project.ext.set(prop.key, prop.value)}
 }
 
+convention.plugins.platformInfo = new PlatformInfo()
+
 allprojects {
     if (path != ":dependencies") {
         evaluationDependsOn(":dependencies")
@@ -34,4 +36,33 @@ allprojects {
             }
         }
     }
+}
+
+class PlatformInfo {
+    private final String osName = System.properties['os.name']
+    private final String osArch = System.properties['os.arch']
+
+    boolean isMac() {
+        return osName == 'Mac OS X'
+    }
+
+    boolean isLinux() {
+        return osName == 'Linux'
+    }
+
+    boolean isAmd64() {
+        return osArch in ['x86_64', 'amd64']
+    }
+
+    String getGnuTriplet() {
+        if (isLinux() && isAmd64()) {
+            return "x86_64-unknown-linux-gnu"
+        } else {
+            throw unsupportedPlatformException()
+        }
+    }
+
+    Throwable unsupportedPlatformException() {
+        return new Error("unsupported platform: $osName/$osArch")
+    }
 }

dependencies/build.gradle

@@ -1,20 +1,12 @@
 abstract class NativeDep extends DefaultTask {
 
-    private static String getCurrentHostTarget() {
-        String osName = System.properties['os.name']
-        String osArch = System.properties['os.arch']
-
-        // TODO: implement more generally
-        if (osArch in ['x86_64', 'amd64']) {
-            if (osName == 'Mac OS X') {
-                return 'darwin-macos'
-            } else if (osName == 'Linux') {
-                return 'linux-x86-64'
-            } else {
-                throw new Error("Unsupported OS: $osName")
-            }
+    private String getCurrentHostTarget() {
+        if (project.isMac() && project.isAmd64()) {
+            return 'darwin-macos'
+        } else if (project.isLinux() && project.isAmd64()) {
+            return 'linux-x86-64'
         } else {
-            throw new Error("Unsupported arch: $osArch")
+            throw project.unsupportedPlatformException()
         }
     }
 
@@ -67,6 +59,7 @@ class TgzNativeDep extends NativeDep {
                 args "xf", archived
             }
         } catch (Throwable e) {
+            e.printStackTrace()
             project.delete(outputDir)
             throw e
         }