#1: Only error when no branches exist and non-master branch specified

SonarQube returns an empty branch list if the project doesn't already exist, which results in an error being thrown telling the user to re-run the scan with no branch parameters set, even if no branch analysis parameters were specified. However, when a project is created through the Web interface, SonarQube automatically creates a default branch named `master` which the scanner picks up as the primary branch and targets if no other parameters are specified. This inconsistency means users can't have SonarQube automatically create projects, but have to use the Web interface to set-up any projects first.

To make the setup consistent, the check for no branches existing is extended to also check if any of the branch parameters have also been specified. This way, if no branches exist but no branch parameters were specified then a `DefaultBranchConfiguration` instance is returned which points the analysis at the a default `master` branch which SonarQube will automatically create. Similarly, if no branches exist but a source branch of master is specified then a `DefaultBranchConfiguration` is also returned, providing a target branch either isn't specified or also points at master.

src/main/java/com/github/mc1arke/sonarqube/plugin/scanner/CommunityBranchConfigurationLoader.java

@@ -18,6 +18,7 @@
  */
 package com.github.mc1arke.sonarqube.plugin.scanner;
 
+import org.apache.commons.lang.StringUtils;
 import org.sonar.api.CoreProperties;
 import org.sonar.api.utils.MessageException;
 import org.sonar.core.config.ScannerProperties;
@@ -54,10 +55,14 @@ public class CommunityBranchConfigurationLoader implements BranchConfigurationLo
     public BranchConfiguration load(Map<String, String> localSettings, Supplier<Map<String, String>> supplier,
                                     ProjectBranches projectBranches, ProjectPullRequests projectPullRequests) {
         if (projectBranches.isEmpty()) {
-            // it would be nice to identify the 'primary' branch directly, but different projects work differently: using any of master, develop, main etc as primary
-            // A project/global configuration entry could be used to drive this in the future, but the current documented SonarQube parameters need followed for now
-            throw MessageException
-                    .of("No branches currently exist in this project. Please scan the main branch without passing any branch parameters.");
+            if (isTargetingDefaultBranch(localSettings)) {
+                return new DefaultBranchConfiguration();
+            } else {
+                // it would be nice to identify the 'primary' branch directly, but different projects work differently: using any of master, develop, main etc as primary
+                // A project/global configuration entry could be used to drive this in the future, but the current documented SonarQube parameters need followed for now
+                throw MessageException
+                        .of("No branches currently exist in this project. Please scan the main branch without passing any branch parameters.");
+            }
         }
         if (BRANCH_ANALYSIS_PARAMETERS.stream().anyMatch(localSettings::containsKey)) {
             return createBranchConfiguration(localSettings.get(ScannerProperties.BRANCH_NAME),
@@ -73,6 +78,13 @@ public BranchConfiguration load(Map<String, String> localSettings, Supplier<Map<
         return new DefaultBranchConfiguration();
     }
 
+    private static boolean isTargetingDefaultBranch(Map<String, String> localSettings) {
+        String name = StringUtils.trimToNull(localSettings.get(ScannerProperties.BRANCH_NAME));
+        String target = StringUtils.trimToNull(localSettings.get(ScannerProperties.BRANCH_TARGET));
+
+        return (null == name || "master".equals(name)) && (null == target || target.equals(name));
+    }
+
     private static BranchConfiguration createBranchConfiguration(String branchName, String branchTarget,
                                                                  Supplier<Map<String, String>> settingsSupplier,
                                                                  ProjectBranches branches) {

src/test/java/com/github/mc1arke/sonarqube/plugin/scanner/CommunityBranchConfigurationLoaderTest.java

@@ -58,16 +58,99 @@ public ExpectedException expectedException() {
     }
 
     @Test
-    public void testExceptionWhenNoExistingBranch() {
+    public void testExceptionWhenNoExistingBranchAndBranchParamsPresent() {
         CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
         ProjectBranches branchInfo = mock(ProjectBranches.class);
         when(branchInfo.isEmpty()).thenReturn(true);
 
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("sonar.branch.name", "dummy");
+
+        expectedException.expect(MessageException.class);
+        expectedException.expectMessage(IsEqual.equalTo(
+                "No branches currently exist in this project. Please scan the main branch without passing any branch parameters."));
+
+        testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class));
+    }
+
+    @Test
+    public void testDefaultConfigWhenNoExistingBranchAndBranchNameParamMaster() {
+        CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
+        ProjectBranches branchInfo = mock(ProjectBranches.class);
+        when(branchInfo.isEmpty()).thenReturn(true);
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("sonar.branch.name", "master");
+
+        assertEquals(DefaultBranchConfiguration.class,
+                     testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class)).getClass());
+    }
+
+    @Test
+    public void testErrorWhenNoExistingBranchAndBranchTargetMasterButNoSourceBranch() {
+        CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
+        ProjectBranches branchInfo = mock(ProjectBranches.class);
+        when(branchInfo.isEmpty()).thenReturn(true);
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("sonar.branch.source", null);
+        parameters.put("sonar.branch.target", "master");
+
+
+        expectedException.expect(MessageException.class);
+        expectedException.expectMessage(IsEqual.equalTo(
+                "No branches currently exist in this project. Please scan the main branch without passing any branch parameters."));
+
+        testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class));
+    }
+
+
+    @Test
+    public void testDefaultConfigWhenNoExistingBranchAndBranchParamsAllMaster() {
+        CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
+        ProjectBranches branchInfo = mock(ProjectBranches.class);
+        when(branchInfo.isEmpty()).thenReturn(true);
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("sonar.branch.name", "master");
+        parameters.put("sonar.branch.target", "master");
+
+        assertEquals(DefaultBranchConfiguration.class,
+                     testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class)).getClass());
+    }
+
+    @Test
+    public void testExceptionWhenNoExistingBranchAndPullRequestAndBranchParametersPresent() {
+        CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
+        ProjectBranches branchInfo = mock(ProjectBranches.class);
+        when(branchInfo.isEmpty()).thenReturn(true);
+
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("sonar.branch.name", "dummy");
+        parameters.put("sonar.pullrequest.branch", "dummy2");
+
+
         expectedException.expect(MessageException.class);
         expectedException.expectMessage(IsEqual.equalTo(
                 "No branches currently exist in this project. Please scan the main branch without passing any branch parameters."));
 
-        testCase.load(new HashMap<>(), supplier, branchInfo, mock(ProjectPullRequests.class));
+        testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class));
+    }
+
+    @Test
+    public void testDefaultBranchInfoWhenNoBranchParametersSpecifiedAndNoBranchesExist() {
+        CommunityBranchConfigurationLoader testCase = new CommunityBranchConfigurationLoader();
+
+        ProjectBranches branchInfo = mock(ProjectBranches.class);
+        when(branchInfo.isEmpty()).thenReturn(true);
+
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put("dummy", "dummy");
+
+
+        assertEquals(DefaultBranchConfiguration.class,
+                     testCase.load(parameters, supplier, branchInfo, mock(ProjectPullRequests.class)).getClass());
     }
 
     @Test