feat: git change detection works on any commit

Author: snakster

cmd/terramate/cli/cli.go

@@ -754,11 +754,11 @@ func (c *cli) setupGit() {
 	}
 
 	if c.parsedArgs.GitChangeBase != "" {
-		c.prj.baseRef = c.parsedArgs.GitChangeBase
+		c.prj.baseRev = c.parsedArgs.GitChangeBase
 	} else if remoteCheckFailed {
-		c.prj.baseRef = c.prj.defaultLocalBaseRef()
+		c.prj.baseRev = c.prj.defaultLocalBaseRef()
 	} else {
-		c.prj.baseRef = c.prj.defaultBaseRef()
+		c.prj.baseRev = c.prj.selectChangeBase()
 	}
 }
 
@@ -2175,7 +2175,7 @@ func (c *cli) gitSafeguardRemoteEnabled() bool {
 func (c *cli) wd() string                   { return c.prj.wd }
 func (c *cli) rootdir() string              { return c.prj.rootdir }
 func (c *cli) cfg() *config.Root            { return &c.prj.root }
-func (c *cli) baseRef() string              { return c.prj.baseRef }
+func (c *cli) baseRef() string              { return c.prj.baseRev }
 func (c *cli) stackManager() *stack.Manager { return c.prj.stackManager }
 func (c *cli) rootNode() hcl.Config         { return c.prj.root.Tree().Node }
 func (c *cli) cred() credential             { return c.cloud.client.Credential.(credential) }

cmd/terramate/cli/project.go

@@ -20,7 +20,7 @@ type project struct {
 	wd             string
 	isRepo         bool
 	root           config.Root
-	baseRef        string
+	baseRev        string
 	normalizedRepo string
 	stackManager   *stack.Manager
 
@@ -139,18 +139,6 @@ func (p *project) isDefaultBranch() bool {
 	return branch == git.DefaultBranch
 }
 
-// defaultBaseRef returns the baseRef for the current git environment.
-func (p *project) defaultBaseRef() string {
-	if p.isDefaultBranch() &&
-		p.remoteDefaultCommit() == p.headCommit() {
-		_, err := p.git.wrapper.RevParse(defaultBranchBaseRef)
-		if err == nil {
-			return defaultBranchBaseRef
-		}
-	}
-	return p.defaultBranchRef()
-}
-
 // defaultLocalBaseRef returns the baseRef in case there's no remote setup.
 func (p *project) defaultLocalBaseRef() string {
 	git := p.gitcfg()
@@ -163,9 +151,58 @@ func (p *project) defaultLocalBaseRef() string {
 	return git.DefaultBranch
 }
 
-func (p project) defaultBranchRef() string {
-	git := p.gitcfg()
-	return git.DefaultRemote + "/" + git.DefaultBranch
+// selectChangeBase returns the revision used for change comparison based on the current Git state.
+func (p *project) selectChangeBase() string {
+	gitcfg := p.gitcfg()
+	gw := p.git.wrapper
+
+	// Try using remote default branch first
+	defaultBranchRev, _ := gw.RevParse(gitcfg.DefaultRemote + "/" + gitcfg.DefaultBranch)
+	if defaultBranchRev == "" {
+		// Fall back to local default branch
+		defaultBranchRev, _ = gw.RevParse(gitcfg.DefaultBranch)
+
+		if defaultBranchRev == "" {
+			// There's no default branch available, so we can't look for a common parent with it.
+			return defaultBranchBaseRef
+		}
+	}
+
+	branch, _ := gw.CurrentBranch()
+
+	// Either we are on a branch or at a detached HEAD.
+	if branch != "" {
+		if branch == gitcfg.DefaultBranch {
+			// We are at the tip of the default branch -> latest default commit.
+			return defaultBranchBaseRef
+		}
+
+		// Fallthrough to common parent if not on default branch
+	} else {
+		headRev, _ := gw.RevParse("HEAD")
+		isDetachedDefaultBranchTip := headRev == defaultBranchRev
+		if isDetachedDefaultBranchTip {
+			// We are at the latest commit of the default branch.
+			return defaultBranchBaseRef
+		}
+
+		isDefaultBranchAncestor, _ := gw.IsFirstParentAncestor("HEAD", defaultBranchRev)
+		if isDefaultBranchAncestor {
+			// We are at an older commit of the default branch.
+			return defaultBranchBaseRef
+		}
+
+		// Fallthrough to common parent if not at commit of default branch
+	}
+
+	commonParentWithDefaultBranch, _ := gw.FindNearestCommonParent(defaultBranchRev, "HEAD")
+	if commonParentWithDefaultBranch != "" {
+		// We have a nearest common parent with the default branch. Similar to the historic merge base.
+		return commonParentWithDefaultBranch
+	}
+
+	// Fall back to default. Should never happen unless running on an isolated commit.
+	return defaultBranchBaseRef
 }
 
 func (p *project) setDefaults() error {