close #102: treat the input # text to fuse() as Markdown instead of R code

Author: yihui

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: litedown
 Type: Package
 Title: A Lightweight Version of R Markdown
-Version: 0.7.1
+Version: 0.7.2
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666", URL = "https://yihui.org")),
     person("Tim", "Taylor", role = "ctb", comment = c(ORCID = "0000-0002-8587-7113")),

NEWS.md

@@ -2,6 +2,8 @@
 
 - The chunk option `results = 'hide'` will imply `collapse = TRUE`, i.e., when text output is hidden, the source blocks will be merged (thanks, @jangorecki, #87). 
 
+- `fuse(text = '# text')` will be treated as Markdown input instead of R code input (thanks, @chuxinyuan, #102).
+
 # CHANGES IN litedown VERSION 0.7
 
 - `pkg_manual()` will exclude help pages with the keyword `internal` (thanks, @TimTaylor, #78).

R/utils.R

@@ -163,7 +163,9 @@ is_output_full = function(x) isTRUE(attr(x, 'full'))
 # test if input is R code or not (this is based on heuristics and may not be robust)
 is_R = function(input, text) {
   if (is_file(input)) grepl('[.][Rrs]$', input) else {
-    !length(grep('^\\s*```+\\{', text)) && !try_error(parse_only(text))
+    # if R code, it must not contain ```{, be syntactically valid, and contain
+    # at least one expression (i.e., not all comments)
+    !length(grep('^\\s*```+\\{', text)) && !try_error(res <- parse_only(text)) && length(res)
   }
 }