[log] IDEA-120178 Check if branch exists before querying Git or Hg

Otherwise both Git and Hg fail with an error "such branch doesn't exist"

plugins/git4idea/src/git4idea/branch/GitBranchesCollection.java

@@ -17,9 +17,11 @@ package git4idea.branch;
 
 import com.intellij.openapi.util.Condition;
 import com.intellij.util.containers.ContainerUtil;
+import git4idea.GitBranch;
 import git4idea.GitLocalBranch;
 import git4idea.GitRemoteBranch;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
 import java.util.Collections;
@@ -58,12 +60,25 @@ public final class GitBranchesCollection {
     return Collections.unmodifiableCollection(myRemoteBranches);
   }
 
-  public GitLocalBranch findLocalBranch(@NotNull final String name) {
-    return ContainerUtil.find(myLocalBranches, new Condition<GitLocalBranch>() {
+  @Nullable
+  public GitLocalBranch findLocalBranch(@NotNull String name) {
+    return findByName(myLocalBranches, name);
+  }
+
+  @Nullable
+  public GitBranch findBranchByName(@NotNull String name) {
+    GitLocalBranch branch = findByName(myLocalBranches, name);
+    return branch != null ? branch : findByName(myRemoteBranches, name);
+  }
+
+  @Nullable
+  private static <T extends GitBranch> T findByName(Collection<T> branches, @NotNull final String name) {
+    return ContainerUtil.find(branches, new Condition<T>() {
       @Override
-      public boolean value(GitLocalBranch branch) {
+      public boolean value(T branch) {
         return name.equals(branch.getName());
       }
     });
   }
+
 }

plugins/git4idea/src/git4idea/log/GitLogProvider.java

@@ -203,7 +203,13 @@ public class GitLogProvider implements VcsLogProvider {
         LOG.warn("More than one branch filter was passed. Using only the first one.");
       }
       VcsLogBranchFilter branchFilter = branchFilters.iterator().next();
-      filterParameters.add(branchFilter.getBranchName());
+      String branch = branchFilter.getBranchName();
+      GitRepository repository = getRepository(root);
+      assert repository != null : "repository is null for root " + root + " but was previously reported as 'ready'";
+      if (repository.getBranches().findBranchByName(branch) == null) {
+        return Collections.emptyList();
+      }
+      filterParameters.add(branch);
     }
     else {
       filterParameters.addAll(GitHistoryUtils.LOG_ALL);

plugins/hg4idea/src/org/zmlx/hg4idea/log/HgLogProvider.java

@@ -166,8 +166,22 @@ public class HgLogProvider implements VcsLogProvider {
 
     // branch filter and user filter may be used several times without delimiter
     if (!branchFilters.isEmpty()) {
+      HgRepository repository = myRepositoryManager.getRepositoryForRoot(root);
+      if (repository == null) {
+        LOG.error("Repository not found for root " + root);
+        return Collections.emptyList();
+      }
+
+      boolean atLeastOneBranchExists = false;
       for (VcsLogBranchFilter branchFilter : branchFilters) {
-        filterParameters.add(prepareParameter("branch", branchFilter.getBranchName()));
+        String branchName = branchFilter.getBranchName();
+        if (branchExists(repository, branchName)) {
+          filterParameters.add(prepareParameter("branch", branchName));
+          atLeastOneBranchExists = true;
+        }
+      }
+      if (!atLeastOneBranchExists) { // no such branches => filter matches nothing
+        return Collections.emptyList();
       }
     }
 
@@ -238,4 +252,10 @@ public class HgLogProvider implements VcsLogProvider {
   private static String prepareParameter(String paramName, String value) {
     return "--" + paramName + "=" + value; // no value escaping needed, because the parameter itself will be quoted by GeneralCommandLine
   }
+
+  private static boolean branchExists(@NotNull HgRepository repository, @NotNull String branchName) {
+    return repository.getBranches().keySet().contains(branchName) ||
+           HgUtil.getNamesWithoutHashes(repository.getBookmarks()).contains(branchName);
+  }
+
 }