[JENKINS-16993] Use "git log" to determine changed files.

The output of "git show" included commits that were not introduced since
the last build, so could falsely trigger build in the presence of
"includedRegions".

A benefit of not including extraneous commits is the size of the output
is reduced, and therefore less heap required.

This can still trigger extra builds as "-m" means the changes between all
legs of a merge commit are displayed.  However, without this, conflict
resolution changed as part of the merge commit would be skipped.

src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java

@@ -326,12 +326,12 @@ public List<String> showRevision(ObjectId from, ObjectId to) throws GitException
     	StringWriter writer = new StringWriter();
 
     	if (from != null){
-    		writer.write(launchCommand("show", "--no-abbrev", "--format=raw", "-M", "--raw",
+    		writer.write(launchCommand("log", "--full-history", "--no-abbrev", "--format=raw", "-M", "-m", "--raw",
                     from.name() + ".." + to.name()));
-    		writer.write("\\n");
+        } else {
+    		writer.write(launchCommand("log", "--full-history", "--no-abbrev", "--format=raw", "-M", "-m", "--raw",
+                    "-1", to.name()));
     	}
-
-    	writer.write(launchCommand("whatchanged", "--no-abbrev", "-M", "-m", "--pretty=raw", "-1", to.name()));
 
         String result = writer.toString();
         List<String> revShow = new ArrayList<String>();

src/test/java/org/jenkinsci/plugins/gitclient/GitAPITestCase.java

@@ -1,6 +1,7 @@
 package org.jenkinsci.plugins.gitclient;
 
 import com.google.common.base.Function;
+import com.google.common.base.Predicate;
 import com.google.common.collect.Collections2;
 import hudson.Launcher;
 import hudson.model.TaskListener;
@@ -15,6 +16,7 @@
 
 import java.io.*;
 import java.util.Collection;
+import java.util.List;
 import java.util.Set;
 
 /**
@@ -318,6 +320,64 @@ public void test_push() throws Exception {
         assertEquals(sha1, remoteSha1);
     }
 
+    public void test_show_revision_for_merge() throws Exception {
+        launchCommand("git init");
+        launchCommand("git fetch https://github.com/jenkinsci/git-client-plugin.git");
+        ObjectId from = ObjectId.fromString("45e76942914664ee19f31d90e6f2edbfe0d13a46");
+        ObjectId to = ObjectId.fromString("b53374617e85537ec46f86911b5efe3e4e2fa54b");
+
+        List<String> revisionDetails = git.showRevision(from, to);
+
+        Collection<String> commits = Collections2.filter(revisionDetails, new Predicate<String>() {
+            public boolean apply(String detail) {
+                return detail.startsWith("commit ");
+            }
+        });
+        assertEquals(3, commits.size());
+        assertTrue(commits.contains("commit 4f2964e476776cf59be3e033310f9177bedbf6a8"));
+        // Merge commit is duplicated as have to capture changes that may have been made as part of merge
+        assertTrue(commits.contains("commit b53374617e85537ec46f86911b5efe3e4e2fa54b (from 4f2964e476776cf59be3e033310f9177bedbf6a8)"));
+        assertTrue(commits.contains("commit b53374617e85537ec46f86911b5efe3e4e2fa54b (from 45e76942914664ee19f31d90e6f2edbfe0d13a46)"));
+
+        Collection<String> diffs = Collections2.filter(revisionDetails, new Predicate<String>() {
+            public boolean apply(String detail) {
+                return detail.startsWith(":");
+            }
+        });
+        Collection<String> paths = Collections2.transform(diffs, new Function<String, String>() {
+            public String apply(String diff) {
+                return diff.substring(diff.indexOf('\t')+1);
+            }
+        });
+
+        assertTrue(paths.contains(".gitignore"));
+        // Some irrelevant changes will be listed due to merge commit
+        assertTrue(paths.contains("pom.xml"));
+        assertTrue(paths.contains("src/main/java/hudson/plugins/git/GitAPI.java"));
+        assertTrue(paths.contains("src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java"));
+        assertTrue(paths.contains("src/main/java/org/jenkinsci/plugins/gitclient/Git.java"));
+        assertTrue(paths.contains("src/main/java/org/jenkinsci/plugins/gitclient/GitClient.java"));
+        assertTrue(paths.contains("src/main/java/org/jenkinsci/plugins/gitclient/JGitAPIImpl.java"));
+        assertTrue(paths.contains("src/test/java/org/jenkinsci/plugins/gitclient/GitAPITestCase.java"));
+        assertTrue(paths.contains("src/test/java/org/jenkinsci/plugins/gitclient/JGitAPIImplTest.java"));
+        // Previous implementation included other commits, and listed irrelevant changes
+        assertFalse(paths.contains("README.md"));
+    }
+
+    public void test_show_revision_for_single_commit() throws Exception {
+        launchCommand("git init");
+        launchCommand("git fetch https://github.com/jenkinsci/git-client-plugin.git");
+        ObjectId to = ObjectId.fromString("51de9eda47ca8dcf03b2af58dfff7355585f0d0c");
+        List<String> revisionDetails = git.showRevision(null, to);
+        Collection<String> commits = Collections2.filter(revisionDetails, new Predicate<String>() {
+            public boolean apply(String detail) {
+                return detail.startsWith("commit ");
+            }
+        });
+        assertEquals(1, commits.size());
+        assertTrue(commits.contains("commit 51de9eda47ca8dcf03b2af58dfff7355585f0d0c"));
+    }
+
     private String launchCommand(String args) throws IOException, InterruptedException {
         return launchCommand(repo, args);
     }

src/test/java/org/jenkinsci/plugins/gitclient/JGitAPIImplTest.java

@@ -39,6 +39,8 @@ public static Test suite() {
         suite.addTest(TestSuite.createTest(JGitAPIImplTest.class, "test_hasGitRepo_without_git_directory"));
         suite.addTest(TestSuite.createTest(JGitAPIImplTest.class, "test_hasGitRepo_with_invalid_git_repo"));
         suite.addTest(TestSuite.createTest(JGitAPIImplTest.class, "test_hasGitRepo_with_valid_git_repo"));
+        //suite.addTest(TestSuite.createTest(JGitAPIImplTest.class, "test_show_revision_for_merge"));
+        //suite.addTest(TestSuite.createTest(JGitAPIImplTest.class, "test_show_revision_for_single_commit"));
 
         return suite;
     }