Compare branches, commits and tags with each other (#6991)

* Supports tags when comparing commits or branches

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Hide headline when only comparing and don't load unused data

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Merges compare logics to allow comparing branches, commits and tags with eachother

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Display branch or tag instead of commit when used for comparing

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Show pull request form after click on button

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Transfers relevant pull.go changes from master to compare.go

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Fixes error when comparing forks against a commit or tag

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Removes console.log from JavaScript file

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Show icon next to commit reference when comparing branch or tag

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Updates css file

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Fixes import order

* Renames template variable

* Update routers/repo/compare.go

Co-Authored-By: zeripath <art27@cantab.net>

* Update from master

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Allow short-shas in compare

* Renames prInfo to compareInfo

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Check PR permissions only if compare is pull request

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adjusts comment

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Use compareInfo instead of prInfo

3 files changed, 43 insertions, 21 deletions

diff --git a/modules/git/repo_commit.go b/modules/git/repo_commit.go
index b631f9341e..501ea88e40 100644
--- a/modules/git/repo_commit.go
+++ b/modules/git/repo_commit.go
@@ -27,6 +27,16 @@ func (repo *Repository) GetRefCommitID(name string) (string, error) {
 	return ref.Hash().String(), nil
 }
 
+// IsCommitExist returns true if given commit exists in current repository.
+func (repo *Repository) IsCommitExist(name string) bool {
+	hash := plumbing.NewHash(name)
+	_, err := repo.gogitRepo.CommitObject(hash)
+	if err != nil {
+		return false
+	}
+	return true
+}
+
 // GetBranchCommitID returns last commit ID string of given branch.
 func (repo *Repository) GetBranchCommitID(name string) (string, error) {
 	return repo.GetRefCommitID(BranchPrefix + name)
diff --git a/modules/git/repo_pull.go b/modules/git/repo_compare.go
index 65c5414551..e7a1d72a85 100644
--- a/modules/git/repo_pull.go
+++ b/modules/git/repo_compare.go
@@ -1,4 +1,5 @@
 // Copyright 2015 The Gogs Authors. All rights reserved.
+// Copyright 2019 The Gitea Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
 
@@ -14,55 +15,66 @@ import (
 	"time"
 )
 
-// PullRequestInfo represents needed information for a pull request.
-type PullRequestInfo struct {
+// CompareInfo represents needed information for comparing references.
+type CompareInfo struct {
 	MergeBase string
 	Commits   *list.List
 	NumFiles  int
 }
 
 // GetMergeBase checks and returns merge base of two branches.
-func (repo *Repository) GetMergeBase(base, head string) (string, error) {
+func (repo *Repository) GetMergeBase(tmpRemote string, base, head string) (string, error) {
+	if tmpRemote == "" {
+		tmpRemote = "origin"
+	}
+
+	if tmpRemote != "origin" {
+		tmpBaseName := "refs/remotes/" + tmpRemote + "/tmp_" + base
+		// Fetch commit into a temporary branch in order to be able to handle commits and tags
+		_, err := NewCommand("fetch", tmpRemote, base+":"+tmpBaseName).RunInDir(repo.Path)
+		if err == nil {
+			base = tmpBaseName
+		}
+	}
+
 	stdout, err := NewCommand("merge-base", base, head).RunInDir(repo.Path)
 	return strings.TrimSpace(stdout), err
 }
 
-// GetPullRequestInfo generates and returns pull request information
-// between base and head branches of repositories.
-func (repo *Repository) GetPullRequestInfo(basePath, baseBranch, headBranch string) (_ *PullRequestInfo, err error) {
-	var remoteBranch string
+// GetCompareInfo generates and returns compare information between base and head branches of repositories.
+func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string) (_ *CompareInfo, err error) {
+	var (
+		remoteBranch string
+		tmpRemote    string
+	)
 
 	// We don't need a temporary remote for same repository.
 	if repo.Path != basePath {
 		// Add a temporary remote
-		tmpRemote := strconv.FormatInt(time.Now().UnixNano(), 10)
+		tmpRemote = strconv.FormatInt(time.Now().UnixNano(), 10)
 		if err = repo.AddRemote(tmpRemote, basePath, true); err != nil {
 			return nil, fmt.Errorf("AddRemote: %v", err)
 		}
 		defer repo.RemoveRemote(tmpRemote)
-
-		remoteBranch = "remotes/" + tmpRemote + "/" + baseBranch
-	} else {
-		remoteBranch = baseBranch
 	}
 
-	prInfo := new(PullRequestInfo)
-	prInfo.MergeBase, err = repo.GetMergeBase(remoteBranch, headBranch)
+	compareInfo := new(CompareInfo)
+	compareInfo.MergeBase, err = repo.GetMergeBase(tmpRemote, baseBranch, headBranch)
 	if err == nil {
 		// We have a common base
-		logs, err := NewCommand("log", prInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
+		logs, err := NewCommand("log", compareInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
 		if err != nil {
 			return nil, err
 		}
-		prInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
+		compareInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
 		if err != nil {
 			return nil, fmt.Errorf("parsePrettyFormatLogToList: %v", err)
 		}
 	} else {
-		prInfo.Commits = list.New()
-		prInfo.MergeBase, err = GetFullCommitID(repo.Path, remoteBranch)
+		compareInfo.Commits = list.New()
+		compareInfo.MergeBase, err = GetFullCommitID(repo.Path, remoteBranch)
 		if err != nil {
-			prInfo.MergeBase = remoteBranch
+			compareInfo.MergeBase = remoteBranch
 		}
 	}
 
@@ -71,9 +83,9 @@ func (repo *Repository) GetPullRequestInfo(basePath, baseBranch, headBranch stri
 	if err != nil {
 		return nil, err
 	}
-	prInfo.NumFiles = len(strings.Split(stdout, "\n")) - 1
+	compareInfo.NumFiles = len(strings.Split(stdout, "\n")) - 1
 
-	return prInfo, nil
+	return compareInfo, nil
 }
 
 // GetPatch generates and returns patch data between given revisions.
diff --git a/modules/git/repo_pull_test.go b/modules/git/repo_compare_test.go
index e194788773..e194788773 100644
--- a/modules/git/repo_pull_test.go
+++ b/modules/git/repo_compare_test.go