From f7e2d238797e59d7be7bfaff9ad5e0b142640e8c Mon Sep 17 00:00:00 2001
From: Doug Davis <dug@us.ibm.com>
Date: Fri, 19 Feb 2016 11:17:15 -0800
Subject: [PATCH] Optimize .dockerignore when there are exclusions

Closes #20470

Before this PR we used to scan the entire build context when there were
exclusions in the .dockerignore file (paths that started with !). Now we
only traverse into subdirs when one of the exclusions starts with that dir
path.

Signed-off-by: Doug Davis <dug@us.ibm.com>
---
 archive/archive.go | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/archive/archive.go b/archive/archive.go
index a63a720..358ab09 100644
--- a/archive/archive.go
+++ b/archive/archive.go
@@ -582,10 +582,36 @@ func TarWithOptions(srcPath string, options *TarOptions) (io.ReadCloser, error)
 				}
 
 				if skip {
-					if !exceptions && f.IsDir() {
+					// If we want to skip this file and its a directory
+					// then we should first check to see if there's an
+					// excludes pattern (eg !dir/file) that starts with this
+					// dir. If so then we can't skip this dir.
+
+					// Its not a dir then so we can just return/skip.
+					if !f.IsDir() {
+						return nil
+					}
+
+					// No exceptions (!...) in patterns so just skip dir
+					if !exceptions {
 						return filepath.SkipDir
 					}
-					return nil
+
+					dirSlash := relFilePath + string(filepath.Separator)
+
+					for _, pat := range patterns {
+						if pat[0] != '!' {
+							continue
+						}
+						pat = pat[1:] + string(filepath.Separator)
+						if strings.HasPrefix(pat, dirSlash) {
+							// found a match - so can't skip this dir
+							return nil
+						}
+					}
+
+					// No matching exclusion dir so just skip dir
+					return filepath.SkipDir
 				}
 
 				if seen[relFilePath] {