Added more helpful error dialog for Go language tools empty prefs.

Fixes #209

plugin_ide.core/src/com/googlecode/goclipse/core/GoEnvironmentPrefs.java

@@ -10,18 +10,17 @@
  *******************************************************************************/
 package com.googlecode.goclipse.core;
 
-import melnorme.lang.ide.core.LangCore;
 import melnorme.lang.ide.core.operations.ToolchainPreferences;
 import melnorme.lang.ide.core.utils.prefs.BooleanPreference;
 import melnorme.lang.ide.core.utils.prefs.IProjectPreference;
 import melnorme.lang.ide.core.utils.prefs.OptionalStringPreference;
 
 public interface GoEnvironmentPrefs {
 
-	IProjectPreference<String> GO_PATH = new OptionalStringPreference(LangCore.PLUGIN_ID, 
+	IProjectPreference<String> GO_PATH = new OptionalStringPreference( 
 		"com.googlecode.goclipse.gopath", ToolchainPreferences.USE_PROJECT_SETTINGS).getProjectPreference();
 
-	IProjectPreference<Boolean> APPEND_PROJECT_LOC_TO_GOPATH = new BooleanPreference(LangCore.PLUGIN_ID,
+	IProjectPreference<Boolean> APPEND_PROJECT_LOC_TO_GOPATH = new BooleanPreference(
 		"append_projloc_gopath", true, ToolchainPreferences.USE_PROJECT_SETTINGS).getProjectPreference();
 
 }

plugin_ide.core/src/com/googlecode/goclipse/core/GoToolPreferences.java

@@ -12,23 +12,64 @@
 
 import java.nio.file.Path;
 
-import melnorme.lang.ide.core.LangCore;
+import melnorme.lang.ide.core.LangCore_Actual;
 import melnorme.lang.ide.core.utils.prefs.DerivedValuePreference;
 import melnorme.lang.ide.core.utils.prefs.OptionalStringPreference;
 import melnorme.lang.utils.validators.LocationOrSinglePathValidator;
+import melnorme.lang.utils.validators.PathValidator;
+import melnorme.utilbox.fields.validation.ValidationException;
+import melnorme.utilbox.status.Severity;
 
 public interface GoToolPreferences {
 
-	DerivedValuePreference<Path> GO_GURU_Path = new DerivedValuePreference<Path>(LangCore.PLUGIN_ID, 
-		"GoToolPreferences.GO_GURU_Path", "", null,  
-		(new LocationOrSinglePathValidator("guru path:")).setFileOnly(true));
+	public class GoToolValidator extends LocationOrSinglePathValidator {
+		public GoToolValidator(String fieldNamePrefix) {
+			// TODO: refactor to fieldName
+			super(fieldNamePrefix);
+		}
+
+		@Override
+		protected String getFullMessage(String simpleMessage) {
+			return super.getFullMessage(simpleMessage);
+		}
+
+		@Override
+		protected ValidationException createIsEmptyException() {
+			String baseMsg = fieldNamePrefix + " is not configured."; 
+			String detailsMsg = 
+					"The " + fieldNamePrefix + " setting needs to be configured in the " + 
+					linkGoPreferences() + ".\n" + "See the " + linkUserGuide() + " for more information.";
+			return new ValidationException(Severity.WARNING, baseMsg, detailsMsg);
+		}
+
+		protected String linkGoPreferences() {
+			return linkReference("Go preferences", "pref:" + LangCore_Actual.TOOLS_PREF_PAGE_ID);
+		}
+
+		protected String linkUserGuide() {
+			return linkReference("UserGuide", LangCore_Actual.USER_GUIDE_LINK);
+		}
+
+		public static String linkReference(String text, String target) {
+			return "<a href=\"" + target + "\">" + text + "</a>";
+		}
+	}
 
-	DerivedValuePreference<Path> GODEF_Path = new DerivedValuePreference<Path>(LangCore.PLUGIN_ID, 
+	PathValidator GURU_PATH_validator = new GoToolValidator("guru path");
+	PathValidator GODEF_PATH_validator = new GoToolValidator("godef path");
+	PathValidator GOFMT_PATH_validator = new GoToolValidator("gofmt path");
+
+
+	DerivedValuePreference<Path> GO_GURU_Path = new DerivedValuePreference<Path>( 
+		"GoToolPreferences.GO_GURU_Path", "", null, 
+		GURU_PATH_validator);
+
+	DerivedValuePreference<Path> GODEF_Path = new DerivedValuePreference<Path>( 
 		"GoToolPreferences.godef.Path", "", null, 
-		(new LocationOrSinglePathValidator("godef path:")).setFileOnly(true));
+		GODEF_PATH_validator);
 
 	DerivedValuePreference<Path> GOFMT_Path = new DerivedValuePreference<Path>(
-		new OptionalStringPreference(LangCore.PLUGIN_ID, "GoToolPreferences.GOFMT_Path", null), 
-		(new LocationOrSinglePathValidator("gofmt path:")).setFileOnly(true));
+		new OptionalStringPreference("GoToolPreferences.GOFMT_Path", null), 
+		GOFMT_PATH_validator);
 
 }

plugin_ide.core/src/melnorme/lang/ide/core/LangCore_Actual.java

@@ -28,6 +28,15 @@ public class LangCore_Actual extends AbstractLangCore {
 	public static final String VAR_NAME_SdkToolPath = "GO_TOOL_PATH";
 	public static final String VAR_NAME_SdkToolPath_DESCRIPTION = "The path of the Go tool";
 
+	/* -----------------  ----------------- */
+
+	public static final String USER_GUIDE_LINK = 
+			"https://github.com/GoClipse/goclipse/blob/latest/documentation/UserGuide.md#user-guide";
+	public static final String TOOLS_PREF_PAGE_ID = 
+			"com.googlecode.goclipse.ui.PreferencePages.GocodePreferencePage";
+
+	/* -----------------  ----------------- */
+
 	public LangCore_Actual(ILogHandler logHandler) {
 		super(logHandler);
 	}

plugin_ide.ui/src/com/googlecode/goclipse/ui/GoUIPlugin.java

@@ -10,13 +10,24 @@
  *******************************************************************************/
 package com.googlecode.goclipse.ui;
 
+import static melnorme.utilbox.core.Assert.AssertNamespace.assertFail;
+import static melnorme.utilbox.core.Assert.AssertNamespace.assertNotNull;
+
+import org.eclipse.jface.preference.IPreferenceNode;
+import org.eclipse.jface.preference.PreferenceDialog;
+import org.eclipse.jface.viewers.ISelection;
+import org.eclipse.jface.viewers.IStructuredSelection;
+import org.eclipse.swt.widgets.Shell;
+import org.eclipse.ui.dialogs.PreferencesUtil;
 import org.osgi.framework.BundleContext;
 
 import com.googlecode.goclipse.core.tools.GocodeServerManager;
 import com.googlecode.goclipse.ui.actions.StartGocodeServerOperation;
 
 import melnorme.lang.ide.core.LangCore;
+import melnorme.lang.ide.core.LangCore_Actual;
 import melnorme.lang.ide.ui.LangUIPlugin;
+import melnorme.lang.ide.ui.utils.WorkbenchUtils;
 import melnorme.lang.tooling.common.ops.IOperationMonitor;
 import melnorme.utilbox.concurrency.OperationCancellation;
 import melnorme.utilbox.core.CommonException;
@@ -30,6 +41,24 @@ protected GoOperationsConsoleUIHandler createOperationsConsoleListener() {
 
 	@Override
 	protected void doInitializeAfterLoad(IOperationMonitor om) throws CommonException {
+		checkPrefPageIdIsValid(LangCore_Actual.TOOLS_PREF_PAGE_ID);
+	}
+
+	protected void checkPrefPageIdIsValid(String prefId) {
+		Shell shell = WorkbenchUtils.getActiveWorkbenchShell();
+		PreferenceDialog prefDialog = PreferencesUtil.createPreferenceDialogOn(shell, prefId, null, null);
+		assertNotNull(prefDialog); // Don't create, just eagerly check that it exits, that the ID is correct
+		ISelection selection = prefDialog.getTreeViewer().getSelection();
+		if(selection instanceof IStructuredSelection) {
+			IStructuredSelection ss = (IStructuredSelection) selection;
+			if(ss.getFirstElement() instanceof IPreferenceNode) {
+				IPreferenceNode prefNode = (IPreferenceNode) ss.getFirstElement();
+				if(prefNode.getId().equals(prefId)) {
+					return; // Id exists
+				}
+			}
+		}
+		assertFail();
 	}
 
 	public static GocodeServerManager prepareGocodeManager_inUI()