Add go wrapper around git diff-tree --raw -r -M (#33369)

* Implemented calling git diff-tree
 * Ensures wrapper function is called with valid arguments
 * Parses output into go struct, using strong typing when possible

modules/git/tree_entry_mode.go

@@ -3,7 +3,10 @@
 
 package git
 
-import "strconv"
+import (
+	"fmt"
+	"strconv"
+)
 
 // EntryMode the type of the object in the git tree
 type EntryMode int
@@ -11,6 +14,9 @@ type EntryMode int
 // There are only a few file modes in Git. They look like unix file modes, but they can only be
 // one of these.
 const (
+	// EntryModeNoEntry is possible if the file was added or removed in a commit. In the case of
+	// added the base commit will not have the file in its tree so a mode of 0o000000 is used.
+	EntryModeNoEntry EntryMode = 0o000000
 	// EntryModeBlob
 	EntryModeBlob EntryMode = 0o100644
 	// EntryModeExec
@@ -33,3 +39,22 @@ func ToEntryMode(value string) EntryMode {
 	v, _ := strconv.ParseInt(value, 8, 32)
 	return EntryMode(v)
 }
+
+func ParseEntryMode(mode string) (EntryMode, error) {
+	switch mode {
+	case "000000":
+		return EntryModeNoEntry, nil
+	case "100644":
+		return EntryModeBlob, nil
+	case "100755":
+		return EntryModeExec, nil
+	case "120000":
+		return EntryModeSymlink, nil
+	case "160000":
+		return EntryModeCommit, nil
+	case "040000", "040755": // git uses 040000 for tree object, but some users may get 040755 for unknown reasons
+		return EntryModeTree, nil
+	default:
+		return 0, fmt.Errorf("unparsable entry mode: %s", mode)
+	}
+}