parser: do not consume the newline that ends a heredoc terminator line

src/Language/Docker/Parser/Prelude.hs

@@ -202,8 +202,11 @@ heredocContent marker = do
     termination :: Parser Text
     termination = try terEOL <|> terEOF
 
+    -- The line break that follows the terminating marker is not part of the
+    -- heredoc: it is the line break that separates this instruction from
+    -- whatever comes next, so it is left for the caller to consume.
     terEOL :: Parser Text
-    terEOL = string $ "\n" <> marker <> "\n"
+    terEOL = string ("\n" <> marker) <* lookAhead (char '\n')
 
     terEOF :: Parser Text
     terEOF = do
@@ -215,7 +218,7 @@ heredocContent marker = do
     delimiter = try delEOL <|> delEOF
 
     delEOL :: Parser Text
-    delEOL = string $ marker <> "\n"
+    delEOL = string marker <* lookAhead (char '\n')
 
     delEOF :: Parser Text
     delEOF = do

test/Language/Docker/ParseCopySpec.hs

@@ -314,3 +314,23 @@ spec = do
                   ( CopyArgs [ SourcePath "FOO" ] ( TargetPath "/target" ) )
                   def
               ]
+    it "heredoc followed by another instruction" $
+      let file = Text.unlines ["COPY <<EOF /target", "content", "EOF", "COPY a b"]
+       in assertAst
+            file
+              [ Copy
+                  ( CopyArgs [ SourcePath "EOF" ] ( TargetPath "/target" ) )
+                  def,
+                Copy
+                  ( CopyArgs [ SourcePath "a" ] ( TargetPath "b" ) )
+                  def
+              ]
+    it "empty heredoc followed by a comment" $
+      let file = Text.unlines ["COPY <<EOF /target", "EOF", "# comment"]
+       in assertAst
+            file
+              [ Copy
+                  ( CopyArgs [ SourcePath "EOF" ] ( TargetPath "/target" ) )
+                  def,
+                Comment " comment"
+              ]

test/Language/Docker/ParseRunSpec.hs

@@ -567,6 +567,30 @@ spec = do
       let file = "RUN <<EOF\nEOF"
           flags = def { security = Nothing }
        in assertAst file [ Run $ RunArgs (ArgumentsText "") flags ]
+    it "heredoc followed by a comment" $
+      let file = Text.unlines [ "RUN <<EOF", "echo foo", "EOF", "# comment" ]
+          flags = def { security = Nothing }
+       in assertAst
+            file
+            [ Run $ RunArgs (ArgumentsText "echo foo") flags,
+              Comment " comment"
+            ]
+    it "heredoc followed by another instruction" $
+      let file = Text.unlines [ "RUN <<EOF", "echo foo", "EOF", "RUN echo bar" ]
+          flags = def { security = Nothing }
+       in assertAst
+            file
+            [ Run $ RunArgs (ArgumentsText "echo foo") flags,
+              Run $ RunArgs (ArgumentsText "echo bar") flags
+            ]
+    it "empty heredoc followed by a comment" $
+      let file = Text.unlines [ "RUN <<EOF", "EOF", "# comment" ]
+          flags = def { security = Nothing }
+       in assertAst
+            file
+            [ Run $ RunArgs (ArgumentsText "") flags,
+              Comment " comment"
+            ]
     it "evil heredoc" $
       let file = Text.unlines [ "RUN <<EOF foo", "bar EOF", "EOF"]
           flags = def { security = Nothing }