From a4dd449c68b7124cb653d685c841b6cfdceaf4c9 Mon Sep 17 00:00:00 2001
From: Yihui Xie <xie@yihui.name>
Date: Thu, 10 Oct 2024 08:39:02 -0500
Subject: [PATCH] fix yihui/litedown#34: allow () around math expressions
 (outside dollar signs)

---
 DESCRIPTION                     |  2 +-
 NEWS.md                         |  2 ++
 R/markdown.R                    | 13 +++++++------
 man/protect_math.Rd             |  9 +++++----
 tests/test-cran/test-markdown.R |  7 +++++++
 5 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/DESCRIPTION b/DESCRIPTION
index 3c5f223..938e6eb 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Package: xfun
 Type: Package
 Title: Supporting Functions for Packages Maintained by 'Yihui Xie'
-Version: 0.48.4
+Version: 0.48.5
 Authors@R: c(
   person("Yihui", "Xie", role = c("aut", "cre", "cph"), email = "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666")),
   person("Wush", "Wu", role = "ctb"),
diff --git a/NEWS.md b/NEWS.md
index 4cf5381..6f93206 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -4,6 +4,8 @@
 
 - `protect_math()` will ignore `$ $` if there are backticks after the opening `$` or before the closing `$`, e.g., ``$`this is not math`$``.
 
+- `protect_math()` allows for parentheses `()` around math expressions now, e.g., `($x$)` was previously not recognized but is recognized now (thanks, @AlbertLei, yihui/litedown#34).
+
 - `html_escape()` will not escape double quotes (i.e., convert `"`" to `&quot;`) by default, and the conversion will be done only for `html_escape(attr = TRUE)`.
 
 - Added an argument `start` to `make_fence()`.
diff --git a/R/markdown.R b/R/markdown.R
index c7c8ac9..b79c305 100644
--- a/R/markdown.R
+++ b/R/markdown.R
@@ -56,10 +56,11 @@ prose_index = function(x, warn = TRUE) {
 #'
 #' Expressions in pairs of dollar signs or double dollar signs are treated as
 #' math, if there are no spaces after the starting dollar sign, or before the
-#' ending dollar sign. There should be spaces before the starting dollar sign,
-#' unless the math expression starts from the very beginning of a line. For a
-#' pair of single dollar signs, the ending dollar sign should not be followed by
-#' a number. With these assumptions, there should not be too many false
+#' ending dollar sign. There should be a space or `(` before the starting dollar
+#' sign, unless the math expression starts from the very beginning of a line.
+#' For a pair of single dollar signs, the ending dollar sign should not be
+#' followed by a number, and the inner math expression should not be wrapped in
+#' backticks. With these assumptions, there should not be too many false
 #' positives when detecing math expressions.
 #'
 #' Besides, LaTeX environments (\verb{\begin{*}} and \verb{\end{*}}) are also
@@ -90,7 +91,7 @@ protect_math = function(x, token = '', use_block = FALSE) {
 
 escape_math = function(x, token = '', use_block = FALSE) {
   # replace $x$ with `\(x\)` (protect inline math in <code></code>)
-  m = gregexpr('(?<=^|[\\s])[$](?![ `])[^$]+?(?<![ `])[$](?![$0123456789])', x, perl = TRUE)
+  m = gregexpr('(?<=^|[\\s(])[$](?![ `])[^$]+?(?<![ `])[$](?![$0123456789])', x, perl = TRUE)
   regmatches(x, m) = lapply(regmatches(x, m), function(z) {
     if (length(z) == 0) return(z)
     z = sub('^[$]', paste0('`', token, '\\\\('), z)
@@ -98,7 +99,7 @@ escape_math = function(x, token = '', use_block = FALSE) {
     z
   })
   # replace $$x$$ with `$$x$$` (protect display math)
-  m = gregexpr('(?<=^|[\\s])[$][$](?! )[^$]+?(?<! )[$][$]', x, perl = TRUE)
+  m = gregexpr('(?<=^|[\\s(])[$][$](?! )[^$]+?(?<! )[$][$]', x, perl = TRUE)
   regmatches(x, m) = lapply(regmatches(x, m), function(z) {
     if (length(z) == 0) return(z)
     paste0('`', token, z, token, '`')
diff --git a/man/protect_math.Rd b/man/protect_math.Rd
index d7563ee..bad3022 100644
--- a/man/protect_math.Rd
+++ b/man/protect_math.Rd
@@ -32,10 +32,11 @@ math expressions in Markdown (by heuristics), and wrap them in backticks.
 \details{
 Expressions in pairs of dollar signs or double dollar signs are treated as
 math, if there are no spaces after the starting dollar sign, or before the
-ending dollar sign. There should be spaces before the starting dollar sign,
-unless the math expression starts from the very beginning of a line. For a
-pair of single dollar signs, the ending dollar sign should not be followed by
-a number. With these assumptions, there should not be too many false
+ending dollar sign. There should be a space or \code{(} before the starting dollar
+sign, unless the math expression starts from the very beginning of a line.
+For a pair of single dollar signs, the ending dollar sign should not be
+followed by a number, and the inner math expression should not be wrapped in
+backticks. With these assumptions, there should not be too many false
 positives when detecing math expressions.
 
 Besides, LaTeX environments (\verb{\begin{*}} and \verb{\end{*}}) are also
diff --git a/tests/test-cran/test-markdown.R b/tests/test-cran/test-markdown.R
index 137fc22..883be27 100644
--- a/tests/test-cran/test-markdown.R
+++ b/tests/test-cran/test-markdown.R
@@ -51,6 +51,10 @@ assert('prose_index() works', {
 assert('protect_math() puts inline math expressions in backticks', {
   (protect_math('$x$') %==% '`\\(x\\)`')
   (protect_math('$x$', '===') %==% '`===\\(x\\)===`')
+  (protect_math('($x$)') %==% '(`\\(x\\)`)')
+  (protect_math(' $x$') %==% ' `\\(x\\)`')
+  (protect_math('.$x$') %==% '.$x$')
+  (protect_math('$`x`$') %==% '$`x`$')
   (protect_math('hi $x$ a') %==% 'hi `\\(x\\)` a')
   (protect_math('$ a $') %==% '$ a $')
   (protect_math(' $a$') %==% ' `\\(a\\)`')
@@ -63,6 +67,9 @@ assert('protect_math() puts inline math expressions in backticks', {
 
   (protect_math('$$a$$') %==% '`$$a$$`')
   (protect_math('$$a$') %==% '$$a$')
+  (protect_math('($$a$$)') %==% '(`$$a$$`)')
+  (protect_math(' $$a$$') %==% ' `$$a$$`')
+  (protect_math('.$$a$$') %==% '.$$a$$')
   (protect_math('hi $$\alpha$$') %==% 'hi `$$\alpha$$`')
   (protect_math('hi $$\alpha $$') %==% 'hi $$\alpha $$')
   (protect_math('hi $$ \alpha$$') %==% 'hi $$ \alpha$$')