Allow continuation after comments

This fix is to address moby#29005 where continuation after comments
are not allowed after moby#24725.

This fix made the change so that moby#29005 could be addressed.

An integration test has been added. Other related tests have
been udpated to conform to the behavior changes.

This fix fixes moby#29005, but please feel free for any additional
suggestions.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

builder/dockerfile/parser/parser.go

@@ -176,17 +176,16 @@ func Parse(rwc io.Reader, d *Directive) (*Node, error) {
 				newline := scanner.Text()
 				currentLine++
 
-				// If escape followed by a comment line then stop
-				// Note here that comment line starts with `#` at
-				// the first pos of the line
-				if stripComments(newline) == "" {
-					break
-				}
-
 				// If escape followed by an empty line then stop
 				if strings.TrimSpace(newline) == "" {
 					break
 				}
+
+				// If escape followed by a comment line then we continue.
+				if strings.HasPrefix(strings.TrimSpace(newline), "#") {
+					continue
+				}
+
 				line, child, err = ParseLine(line+newline, d, false)
 				if err != nil {
 					return nil, err

builder/dockerfile/parser/testfiles/continueIndent/Dockerfile

@@ -27,5 +27,6 @@ bye\
 frog
 
 RUN echo hello \
-# this is a comment that breaks escape continuation
-RUN echo this is some more useful stuff
+# this is a comment
+  # this is a comment not starting from pos 1
+this is some more useful stuff

builder/dockerfile/parser/testfiles/continueIndent/result

@@ -6,5 +6,4 @@
 (run "echo hi   world  goodnight")
 (run "echo goodbyefrog")
 (run "echo goodbyefrog")
-(run "echo hello")
-(run "echo this is some more useful stuff")
+(run "echo hello this is some more useful stuff")

integration-cli/docker_cli_build_test.go

@@ -7159,21 +7159,6 @@ RUN echo z
 	c.Assert(out, checker.Contains, "Step 2/4 : RUN echo x")
 	c.Assert(out, checker.Contains, "Step 3/4 : RUN echo y")
 	c.Assert(out, checker.Contains, "Step 4/4 : RUN echo z")
-
-	// With comment, see #24693
-	name = "testbuildcommentandemptylineafterescape"
-	_, out, err = buildImageWithOut(name,
-		`
-FROM busybox
-RUN echo grafana && \
-    echo raintank \
-#echo env-load
-RUN echo vegeta
-`, true)
-	c.Assert(err, checker.IsNil)
-	c.Assert(out, checker.Contains, "Step 1/3 : FROM busybox")
-	c.Assert(out, checker.Contains, "Step 2/3 : RUN echo grafana &&     echo raintank")
-	c.Assert(out, checker.Contains, "Step 3/3 : RUN echo vegeta")
 }
 
 func (s *DockerSuite) TestBuildSquashParent(c *check.C) {
@@ -7327,3 +7312,22 @@ func (s *DockerSuite) TestBuildWindowsEnvCaseInsensitive(c *check.C) {
 		c.Fatalf("Case insensitive environment variables on Windows failed. Got %s", res)
 	}
 }
+
+// Test case for #29005
+func (s *DockerSuite) TestBuildRunCommentLineAfterEscape(c *check.C) {
+	name := "testbuildcommentlineafterescape"
+
+	_, out, err := buildImageWithOut(name,
+		`
+FROM busybox
+
+RUN echo hi \
+  # wut
+&& echo no \
+# omg
+&& echo yes
+`, true)
+	c.Assert(err, checker.IsNil)
+	c.Assert(out, checker.Contains, "Step 1/2 : FROM busybox")
+	c.Assert(out, checker.Contains, "Step 2/2 : RUN echo hi && echo no && echo yes")
+}