Add support for multiline markdown strings as markdown blocks

This is opt-in for now, requires passing mdstrings=true.

Co-authored-by: CarloLucibello <carlo.lucibello@gmail.com>
Co-authored-by: Fredrik Ekre <ekrefredrik@gmail.com>

docs/src/fileformat.md

@@ -45,7 +45,7 @@ For simple use this is all you need to know. The following additional special sy
 There is also some default convenience replacements that will always be performed, see
 [Default replacements](@ref).
 
-### Multiline comments
+### Multiline comments and markdown strings
 
 Literate version 2.7 adds support for Julia multiline comments for markdown input.
 All multiline comments in the input are rewritten to regular comments as part of the
@@ -71,6 +71,22 @@ is rewritten to
 # This is also markdown.
 ```
 
+Similarly, Literate version 2.9 adds support for using literal markdown strings,
+`md""" ... """`, for the markdown sections, for example
+
+```julia
+md"""
+# Title
+blah blah blah
+"""
+```
+is rewritten to
+```julia
+# # Title
+# blah blah blah
+```
+This is not enabled by default -- it requires passing `mdstrings=true`.
+`Literate.markdown`/`Literate.notebook`/`Literate.script`.
 
 ## [**2.2.** Filtering lines](@id Filtering-lines)
 
@@ -104,7 +120,7 @@ is a case where we can prepend `#md` to those lines:
 #md # ```@docs
 #md # Literate.markdown
 #md # Literate.notebook
-#md # Literate.markdown
+#md # Literate.script
 #md # ```
 ````
 The lines in the example above would be filtered out in the preprocessing step, unless we are

src/Literate.jl

@@ -150,14 +150,22 @@ function replace_default(content, sym;
 
     push!(repls, "\r\n" => "\n") # normalize line endings
 
-    # unconditionally rewrite multiline comments to regular comments
+    # unconditionally rewrite multiline comments and
-    multiline_r = r"^#=+$\R^(\X*?)\R^=+#$"m
+    # conditionally multiline markdown strings to regular comments
-    while (m = match(multiline_r, content); m !== nothing)
+    function replace_multiline(multiline_r, str)
+        while (m = match(multiline_r, str); m !== nothing)
             newlines = sprint() do io
                 foreach(l -> println(io, "# ", l), eachline(IOBuffer(m[1])))
             end
-        content = replace(content, multiline_r => chop(newlines); count=1)
+            str = replace(str, multiline_r => chop(newlines); count=1)
         end
+        return str
+    end
+    content = replace_multiline(r"^#=+$\R^(\X*?)\R^=+#$"m, content)
+    if config["mdstrings"]::Bool
+        content = replace_multiline(r"^md\"\"\"$\R^(\X*?)\R^\"\"\"$"m, content)
+    end
+
 
     # unconditionally remove #src lines
     push!(repls, r"^#src.*\n?"m => "") # remove leading #src lines
@@ -245,6 +253,7 @@ function create_configuration(inputfile; user_config, user_kwargs, type=nothing)
     cfg["postprocess"] = identity
     cfg["flavor"] = type === (:md) ? DocumenterFlavor() : DefaultFlavor()
     cfg["credit"] = true
+    cfg["mdstrings"] = false
     cfg["keep_comments"] = false
     cfg["execute"] = type === :md ? false : true
     cfg["codefence"] = get(user_config, "flavor", cfg["flavor"]) isa DocumenterFlavor &&
@@ -439,7 +448,7 @@ function script(inputfile, outputdir=pwd(); config::Dict=Dict(), kwargs...)
             write(ioscript, '\n') # add a newline between each chunk
         elseif isa(chunk, MDChunk) && config["keep_comments"]::Bool
             for line in chunk.lines
-                write(ioscript, rstrip(line.first * "# " * line.second * '\n'))
+                write(ioscript, rstrip(line.first * "# " * line.second) * '\n')
             end
             write(ioscript, '\n') # add a newline between each chunk
         end

test/runtests.jl

@@ -436,6 +436,58 @@ const GITLAB_ENV = Dict(
             @test occursin("# First multiline", script)
             @test occursin("# Second multiline comment", script)
 
+            # mdstrings
+            mdstrings_file = "inputfile_mdstrings.jl"
+            write(mdstrings_file, """
+            md\"\"\"
+            # Markdown header
+
+            Content of the multiline markdown
+            string
+            \"\"\"
+            #-
+            #===
+            # Markdown header 2
+
+            Content of the multiline
+            comment
+            ===#
+            2 + 2
+            """)
+            Literate.script(mdstrings_file, outdir,
+                keep_comments = true, credit=false)
+            script = read(joinpath(outdir, mdstrings_file), String)
+            @test strip(script) == """
+            md\"\"\"
+
+            # Markdown header
+
+            Content of the multiline markdown
+            string
+            \"\"\"
+
+            # # Markdown header 2
+            #
+            # Content of the multiline
+            # comment
+
+            2 + 2"""
+            Literate.script(mdstrings_file, outdir,
+                keep_comments = true, mdstrings = true, credit=false)
+            script = read(joinpath(outdir, mdstrings_file), String)
+            @test strip(script) == """
+            # # Markdown header
+            #
+            # Content of the multiline markdown
+            # string
+
+            # # Markdown header 2
+            #
+            # Content of the multiline
+            # comment
+
+            2 + 2"""
+
             # verify that inputfile exists
             @test_throws ArgumentError Literate.script("nonexistent.jl", outdir)
 
@@ -705,6 +757,11 @@ end end
             @test !occursin("name: inputfile", markdown)
             @test !occursin("name: @__NAME__", markdown)
 
+            # mdstrings
+            Literate.markdown(inputfile, outdir, mdstrings = true)
+            markdown = read(joinpath(outdir, "inputfile.md"), String)
+            @test !occursin("md\"\"\"", markdown)
+
             # execute
             write(inputfile, """
                 using DisplayAs