frontend/dockerfile: Chomp heredoc before parsing shebang

Fixes: #5383
Signed-off-by: Matt Coster <opensource@mtcoster.net>

Author: MTCoster

frontend/dockerfile/dockerfile2llb/convert.go

@@ -1243,7 +1243,12 @@ func dispatchRun(d *dispatchState, c *instructions.RunCommand, proxy *llb.ProxyE
 		}
 
 		if heredoc := parser.MustParseHeredoc(args[0]); heredoc != nil {
-			if d.image.OS != "windows" && strings.HasPrefix(c.Files[0].Data, "#!") {
+			data := c.Files[0].Data
+			if c.Files[0].Chomp {
+				data = parser.ChompHeredocContent(data)
+			}
+
+			if d.image.OS != "windows" && strings.HasPrefix(data, "#!") {
 				// This is a single heredoc with a shebang, so create a file
 				// and run it.
 				// NOTE: choosing to expand doesn't really make sense here, so
@@ -1252,10 +1257,6 @@ func dispatchRun(d *dispatchState, c *instructions.RunCommand, proxy *llb.ProxyE
 				destPath := "/dev/pipes/"
 
 				f := c.Files[0].Name
-				data := c.Files[0].Data
-				if c.Files[0].Chomp {
-					data = parser.ChompHeredocContent(data)
-				}
 				st := llb.Scratch().Dir(sourcePath).File(
 					llb.Mkfile(f, 0755, []byte(data)),
 					dockerui.WithInternalName("preparing inline document"),
@@ -1272,10 +1273,6 @@ func dispatchRun(d *dispatchState, c *instructions.RunCommand, proxy *llb.ProxyE
 				// the syntax can still be used for shells that don't support
 				// heredocs directly.
 				// NOTE: like above, we ignore the expand option.
-				data := c.Files[0].Data
-				if c.Files[0].Chomp {
-					data = parser.ChompHeredocContent(data)
-				}
 				args = []string{data}
 			}
 			customname += fmt.Sprintf(" (%s)", summarizeHeredoc(c.Files[0].Data))

frontend/dockerfile/dockerfile_heredoc_test.go

@@ -295,16 +295,26 @@ func testRunShebangHeredoc(t *testing.T, sb integration.Sandbox) {
 	dockerfile := []byte(`
 FROM busybox AS build
 
+WORKDIR /dest
+
 RUN <<EOF
 #!/bin/awk -f
 BEGIN {
-	print "hello" >> "/dest"
-	print "world" >> "/dest"
+	print "hello" >> "./out1"
+	print "world" >> "./out1"
 }
 EOF
 
+RUN <<-EOF
+	#!/bin/awk -f
+	BEGIN {
+		print "hello" >> "./out2"
+		print "world" >> "./out2"
+	}
+EOF
+
 FROM scratch
-COPY --from=build /dest /dest
+COPY --from=build /dest /
 `)
 
 	dir := integration.Tmpdir(
@@ -332,9 +342,16 @@ COPY --from=build /dest /dest
 	}, nil)
 	require.NoError(t, err)
 
-	dt, err := os.ReadFile(filepath.Join(destDir, "dest"))
-	require.NoError(t, err)
-	require.Equal(t, "hello\nworld\n", string(dt))
+	contents := map[string]string{
+		"out1": "hello\nworld\n",
+		"out2": "hello\nworld\n",
+	}
+
+	for name, content := range contents {
+		dt, err := os.ReadFile(filepath.Join(destDir, name))
+		require.NoError(t, err)
+		require.Equal(t, content, string(dt))
+	}
 }
 
 func testRunComplexHeredoc(t *testing.T, sb integration.Sandbox) {