Fix in-line math output in HTMLWriter

CHANGELOG.md

@@ -3,6 +3,12 @@
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+* Fixed display of inline LaTeX math `$ ... $` in HTMLWriter ([#2281])
+
 ## Version [v1.0.1] - 2023-09-18
 
 ### Fixed
@@ -1683,6 +1689,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#2259]: https://github.com/JuliaDocs/Documenter.jl/issues/2259
 [#2260]: https://github.com/JuliaDocs/Documenter.jl/issues/2260
 [#2269]: https://github.com/JuliaDocs/Documenter.jl/issues/2269
+[#2281]: https://github.com/JuliaDocs/Documenter.jl/issues/2281
 [JuliaLang/julia#29344]: https://github.com/JuliaLang/julia/issues/29344
 [JuliaLang/julia#36953]: https://github.com/JuliaLang/julia/issues/36953
 [JuliaLang/julia#38054]: https://github.com/JuliaLang/julia/issues/38054

src/html/HTMLWriter.jl

@@ -2389,17 +2389,15 @@
     end
     # Check for some 'fallback' MIMEs, defaulting to 'text/plain' if we can't find any of them.
     return if haskey(d, MIME"text/latex"())
-        # If the show(io, ::MIME"text/latex", x) output is already wrapped in \[ ... \] or $$ ... $$, we
-        # unwrap it first, since when we output Markdown.LaTeX objects we put the correct
-        # delimiters around it anyway.
         latex = d[MIME"text/latex"()]
-        # Make sure to match multiline strings!
-        m_bracket = match(r"\s*\\\[(.*)\\\]\s*"s, latex)
-        m_dollars = match(r"\s*\$\$(.*)\$\$\s*"s, latex)
-        out = if m_bracket === nothing && m_dollars === nothing
+        # If the show(io, ::MIME"text/latex", x) output is already wrapped in
+        # \[ ... \] or $$ ... $$, we unwrap it first, since when we output
+        # Markdown.LaTeX objects we put the correct delimiters around it anyway.
+        has_math, latex = _strip_latex_math_delimiters(latex)
+        out = if !has_math
             Documenter.mdparse(latex; mode = :single)
         else
-            [MarkdownAST.@ast MarkdownAST.DisplayMath(m_bracket !== nothing ? m_bracket[1] : m_dollars[1])]
+            [MarkdownAST.@ast MarkdownAST.DisplayMath(latex)]
         end
         domify(dctx, out)
     elseif haskey(d, MIME"text/markdown"())
@@ -2415,6 +2413,21 @@
     end
 end
 
+function _strip_latex_math_delimiters(latex::AbstractString)
+    # Make sure to match multiline strings!
+    m_bracket = match(r"\s*\\\[(.*)\\\]\s*"s, latex)
+    if m_bracket !== nothing
+        return true, m_bracket[1]
+    end
+    # This regex matches the strings "$ ... $" and "$$ ... $$", but not
+    # strings with miss-matched dollar signs such as "$ ... $$" or "$$ ... $"
+    m_dollars = match(r"^\s*(\${1,2})([^\$]*)\1\s*$"s, latex)
+    if m_dollars !== nothing
+        return true, m_dollars[2]
+    end
+    return false, latex
+end
+
 function domify_show_image_binary(dctx::DCtx, filetype::AbstractString, d::Dict{MIME,Any})
     @tags img
     mime_name = "image/$filetype"

test/htmlwriter.jl

@@ -4,7 +4,7 @@ using Test
 import MarkdownAST
 using Documenter
 using Documenter: DocSystem
-using Documenter.HTMLWriter: HTMLWriter, generate_version_file, generate_redirect_file, expand_versions
+using Documenter.HTMLWriter: HTMLWriter, generate_version_file, generate_redirect_file, expand_versions, _strip_latex_math_delimiters
 
 function verify_version_file(versionfile, entries)
     @test isfile(versionfile)
@@ -295,5 +295,51 @@ end
         @test html.size_threshold == 12345
         @test html.size_threshold_warn == 1234
     end
+
+    @testset "HTML: _strip_latex_math_delimiters" begin
+        for content in [
+            "a",
+            "x_1",
+            "x_{1} + x_{2}",
+            "\\begin{array}x_1\\\nx_2\\end{array}",
+        ]
+            for (left, right) in [("\\[", "\\]"), ("\$", "\$"), ("\$\$", "\$\$")]
+                for (input, output) in [
+                    content => (false, content),
+                    "$left$content$right" => (true, content),
+                    " $left$content$right" => (true, content),
+                    "$left$content$right " => (true, content),
+                    "\t$left$content$right  " => (true, content),
+                    " \t$left$content$right\t\t" => (true, content),
+                ]
+                    @test _strip_latex_math_delimiters(input) == output
+                end
+            end
+            # Test that miss-matched delimiters are not treated as math
+            # delimiters
+            for (left, right) in [
+                ("\\[", ""),
+                ("\$", ""),
+                ("\$\$", ""),
+                ("", "\\]"),
+                ("", "\$"),
+                ("", "\$\$"),
+                ("\$", "\\]"),
+                ("\$\$", "\$"),
+                ("\$", "\$\$"),
+            ]
+                for input in [
+                    content,
+                    "$left$content$right",
+                    " $left$content$right",
+                    "$left$content$right ",
+                    "\t$left$content$right  ",
+                    " \t$left$content$right\t\t",
+                ]
+                    @test _strip_latex_math_delimiters(input) == (false, input)
+                end
+            end
+        end
+    end
 end
 end