skip evaluation that hangs on bad input

NEWS.md

@@ -30,7 +30,8 @@
 * `get_source_expressions()` no longer fails on R files that match a knitr pattern (#743, #879, #1406, @AshesITR).
 * Parse error lints now appear with the linter name `"error"` instead of `NA` (#1405, @AshesITR).  
   Also, linting no longer runs if the `source_expressions` contain invalid string data that would cause error messages
-  in other linters. 
+  in other linters.
+   + Also precludes hanging on Rmd files with some syntax errors (#1443, @MichaelChirico).
 * `get_source_expressions()` no longer omits trailing non-code lines from knitr files (#1400, #1415, @AshesITR).  
   This fixes the location information for `trailing_blank_lines_linter()` in RMarkdown documents without terminal
   newlines.

R/get_source_expressions.R

@@ -79,12 +79,12 @@ get_source_expressions <- function(filename, lines = NULL) {
   names(source_expression$lines) <- seq_along(source_expression$lines)
   source_expression$content <- get_content(source_expression$lines)
   parsed_content <- get_source_expression(source_expression, error = function(e) lint_parse_error(e, source_expression))
-  top_level_map <- generate_top_level_map(parsed_content)
 
-  if (inherits(e, "lint") && !nzchar(e$line)) {
+  if (inherits(e, "lint") && (is.na(e$line) || !nzchar(e$line))) {
     # Don't create expression list if it's unreliable (invalid encoding or unhandled parse error)
     expressions <- list()
   } else {
+    top_level_map <- generate_top_level_map(parsed_content)
     xml_parsed_content <- safe_parse_to_xml(parsed_content)
 
     expressions <- lapply(

tests/testthat/test-get_source_expressions.R

@@ -281,6 +281,19 @@ test_that("#743, #879, #1406: get_source_expressions works on R files matching a
   expect_null(source_expressions$error)
 })
 
+test_that("Syntax errors in Rmd don't choke lintr", {
+  tmp <- withr::local_tempfile(lines = c(
+    "```{r}",
+    "if (TRUE) {",
+    "  1",
+    # missing `}` here
+    "if (TRUE) {",
+    "}",
+    "```"
+  ))
+  expect_silent(get_source_expressions(tmp))
+})
+
 skip_if_not_installed("patrick")
 # NB: this is just a cursory test for linters not to
 #   fail on files where the XML content is xml_missing;