Fix string interpolation into Markdown.Table and Markdown.List in md"..." strings, fixes #16194. (#37130)

(cherry picked from commit d446c27)

Author: fredrikekre

stdlib/Markdown/src/Julia/interp.jl

@@ -11,9 +11,13 @@ function interpinner(stream::IO, greedy = false)
     startswith(stream, '$') || return
     (eof(stream) || peek(stream, Char) in whitespace) && return
     try
-        return _parse(stream::IOBuffer, greedy = greedy)
+        return _parse(stream, greedy = greedy)
     catch e
-        return
+        if isa(e, Meta.ParseError)
+            return nothing
+        else
+            rethrow()
+        end
     end
 end
 
@@ -39,10 +43,19 @@ end
 
 toexpr(x) = x
 
-toexpr(xs::Vector{Any}) = Expr(:call, GlobalRef(Base,:getindex), Any, map(toexpr, xs)...)
+toexpr(xs::Union{Vector{Any},Vector{Vector{Any}}}) =
+    Expr(:call, GlobalRef(Base,:getindex), Any, map(toexpr, xs)...)
 
 for T in Any[MD, Paragraph, Header, Link, Bold, Italic]
     @eval function toexpr(md::$T)
         Expr(:call, typeof(md), $(map(x->:(toexpr(md.$x)), fieldnames(Base.unwrap_unionall(T)))...))
     end
 end
+
+function toexpr(md::Table)
+    Expr(:call, Table, toexpr(md.rows), md.align)
+end
+
+function toexpr(md::List)
+    Expr(:call, List, toexpr(md.items), md.ordered, md.loose)
+end

stdlib/Markdown/test/runtests.jl

@@ -1138,3 +1138,23 @@ let m = Markdown.parse("---"), io = IOBuffer()
     show(io, "text/latex", m)
     @test String(take!(io)) == "\\rule{\\textwidth}{1pt}\n"
 end
+
+# issue #16194: interpolation in md"..." strings
+@testset "issue #16194: interpolation in md\"...\" strings" begin
+    x = "X"
+    contains_X(md) = occursin(x, sprint(show, MIME("text/plain"), md))
+    @test contains_X(md"# $x") # H1
+    @test contains_X(md"## $x") # H2
+    @test contains_X(md"### $x") # H3
+    @test contains_X(md"x = $x") # Paragraph
+    @test contains_X(md"- $x") # List
+    @test contains_X(md"[$x](..)") # Link
+    @test contains_X(md"**$x**") # Bold
+    @test contains_X(md"*$x*") # Italic
+    @test contains_X( # Table
+        md"""
+        | name |
+        |------|
+        |  $x  |
+        """)
+end