only injects properties into every reactor project once

Enabling `injectAllReactorProjects` in large and old reactor projects
allows to avoid repeatedly parsing the git history to retrieve the
information.

In the apache/james-project enabling this property allowed to lower the
time spent in git-commit-id from 39s[1] to 2s[2].

However, looking at the verbose logs one can see that the plugin keeps
injecting the properties into every reactor project for every project
where the plugin runs.

This commit aims to avoid reinjecting keys which have already been set
in the context.

[1] https://ge.apache.org/s/xumcl7ztpkmhw/timeline?collapse-all&outcome=success,failed&view=by-type
[2] https://ge.apache.org/s/gpnevfknmdv5a/timeline?collapse-all&hide-timeline&outcome=success,failed&view=by-type

src/main/java/pl/project13/maven/git/GitCommitIdMojo.java

@@ -1234,6 +1234,17 @@ public void error(String msg, Throwable t) {
         commitIdPropertiesOutputFormat = CommitIdPropertiesOutputFormat.PROPERTIES;
       }
 
+      Properties properties = null;
+      // check if properties have already been injected
+      Properties contextProperties = getContextProperties(project);
+      boolean alreadyInjected = injectAllReactorProjects && contextProperties != null;
+      if (alreadyInjected) {
+        log.info(
+                "injectAllReactorProjects is enabled - attempting to use the already computed values");
+        // makes sure the existing context properties are not mutated
+        properties = new Properties(contextProperties);
+      }
+
       final GitCommitIdPlugin.Callback cb =
           new GitCommitIdPlugin.Callback() {
             @Override
@@ -1339,7 +1350,7 @@ public boolean shouldGenerateGitPropertiesFile() {
 
             @Override
             public void performPublishToAllSystemEnvironments(Properties properties) {
-              publishToAllSystemEnvironments(getLogInterface(), properties);
+          publishToAllSystemEnvironments(getLogInterface(), properties, contextProperties);
             }
 
             @Override
@@ -1393,29 +1404,27 @@ public boolean shouldPropertiesEscapeUnicode() {
             }
           };
 
-      Properties properties = null;
-      // check if properties have already been injected
-      Properties contextProperties = getContextProperties(project);
-      boolean alreadyInjected = injectAllReactorProjects && contextProperties != null;
-      if (alreadyInjected) {
-        log.info(
-            "injectAllReactorProjects is enabled - attempting to use the already computed values");
-        properties = contextProperties;
-      }
-
       GitCommitIdPlugin.runPlugin(cb, properties);
     } catch (GitCommitIdExecutionException e) {
       throw new MojoExecutionException(e.getMessage(), e);
     }
   }
 
-  private void publishToAllSystemEnvironments(LogInterface log, Properties propertiesToPublish) {
+  private void publishToAllSystemEnvironments(LogInterface log, Properties propertiesToPublish, Properties contextProperties) {
     publishPropertiesInto(propertiesToPublish, project.getProperties());
     // some plugins rely on the user properties (e.g. flatten-maven-plugin)
     publishPropertiesInto(propertiesToPublish, session.getUserProperties());
 
     if (injectAllReactorProjects) {
-      appendPropertiesToReactorProjects(log, propertiesToPublish);
+      Properties diffPropertiesToPublish = new Properties();
+      propertiesToPublish.forEach((k, v) -> {
+          if (!contextProperties.contains(k)) {
+              diffPropertiesToPublish.setProperty(k.toString(), v.toString());
+          }
+      });
+      if(!diffPropertiesToPublish.isEmpty()) {
+          appendPropertiesToReactorProjects(log, diffPropertiesToPublish);
+      }
     }
 
     if (injectIntoSysProperties) {
@@ -1479,7 +1488,7 @@ private void publishPropertiesInto(Properties propertiesToPublish, Properties pr
   private void appendPropertiesToReactorProjects(LogInterface log, Properties propertiesToPublish) {
     for (MavenProject mavenProject : reactorProjects) {
       log.debug("Adding properties to project: '" + mavenProject.getName() + "'");
-
+      if(mavenProject.equals(project)) continue;
       publishPropertiesInto(propertiesToPublish, mavenProject.getProperties());
       mavenProject.setContextValue(CONTEXT_KEY, propertiesToPublish);
     }