Fix text/latex output in HTMLWriter

src/Writers/HTMLWriter.jl

@@ -1646,7 +1646,11 @@ function mdconvert(d::Dict{MIME,Any}, parent; kwargs...)
     elseif haskey(d, MIME"image/jpeg"())
         out = Documents.RawHTML(string("<img src=\"data:image/jpeg;base64,", d[MIME"image/jpeg"()], "\" />"))
     elseif haskey(d, MIME"text/latex"())
-        out = Utilities.mdparse(d[MIME"text/latex"()]; mode = :single)
+        # If the show(io, ::MIME"text/latex", x) output is already wrapped in \[ ... \], we
+        # unwrap it first, since when we output Markdown.LaTeX objects we put the correct
+        # delimiters around it anyway.
+        m = match(r"\s*\\\[(.*)\\\]\s*", d[MIME"text/latex"()])
+        out = Markdown.LaTeX(m === nothing ? d[MIME"text/latex"()] : m[1])
     elseif haskey(d, MIME"text/markdown"())
         out = Markdown.parse(d[MIME"text/markdown"()])
     elseif haskey(d, MIME"text/plain"())

test/examples/src/man/tutorial.md

@@ -385,3 +385,27 @@ Hello World!
 Written in <a href="https://fonts.google.com/specimen/Nanum+Brush+Script">Nanum Brush Script.</a>
 </div>
 ```
+
+## Handling of `text/latex`
+
+You can define a type that has a `Base.show` method for the `text/latex` MIME:
+
+```@example showablelatex
+struct LaTeXEquation
+    code :: String
+end
+Base.show(io, ::MIME"text/latex", latex::LaTeXEquation) = write(io, latex.code)
+nothing # hide
+```
+
+In an `@example` or `@eval`block, it renders as an equation:
+
+```@example showablelatex
+LaTeXEquation("x^2")
+```
+
+Documenter also supports having the LaTeX text being already wrapped in `\[ ... \]`.
+
+```@example showablelatex
+LaTeXEquation("\\[\\left[ \\begin{array}{rr}x&2 x\\end{array}\\right]\\]")
+```