Refactor C linters for better extensibility/reuse (#6346)

Most importantly, we can run `readLines()` + preprocess the file only once, then pass that output to each linter.

.ci/linters/c/alloc_linter.R

@@ -2,32 +2,32 @@
 # More specifically, given that this is an AST-ignorant checker,
 #   1. Find groups of malloc()/calloc() calls
 #   2. Check the next line for a check like 'if (!x || !y)'
-alloc_linter = function(c_file) {
-  lines <- readLines(c_file)
+alloc_linter = function(c_obj) {
+  lines = c_obj$lines
   # Be a bit more precise to avoid mentions in comments
-  alloc_lines <- grep(R"{=\s*([(]\w+\s*[*][)])?[mc]alloc[(]}", lines)
+  alloc_lines = grep(R"{=\s*([(]\w+\s*[*][)])?[mc]alloc[(]}", lines)
   if (!length(alloc_lines)) return()
   # int *tmp=(int*)malloc(...); or just int tmp=malloc(...);
-  alloc_keys <- lines[alloc_lines] |>
+  alloc_keys = lines[alloc_lines] |>
     strsplit(R"(\s*=\s*)") |>
     vapply(head, 1L, FUN.VALUE="") |>
     trimws() |>
     # just normalize the more exotic assignments, namely 'type *restrict key = ...'
     gsub(pattern = "[*]\\s*(restrict\\s*)?", replacement = "*") |>
     strsplit("*", fixed=TRUE) |>
     vapply(tail, 1L, FUN.VALUE="")
-  alloc_grp_id <- cumsum(c(TRUE, diff(alloc_lines) != 1L))
+  alloc_grp_id = cumsum(c(TRUE, diff(alloc_lines) != 1L))
 
   # execute by group
   tapply(seq_along(alloc_lines), alloc_grp_id, function(grp_idx) {
-    keys_regex <- paste0("\\s*!\\s*", alloc_keys[grp_idx], "\\s*", collapse = "[|][|]")
-    check_regex <- paste0("if\\s*\\(", keys_regex)
-    check_line <- lines[alloc_lines[tail(grp_idx, 1L)] + 1L]
+    keys_regex = paste0("\\s*!\\s*", alloc_keys[grp_idx], "\\s*", collapse = "[|][|]")
+    check_regex = paste0("if\\s*\\(", keys_regex)
+    check_line = lines[alloc_lines[tail(grp_idx, 1L)] + 1L]
     # Rarely (once in fread.c as of initialization), error checking is handled
     #   but not immediately, so use 'NOCHECK' to escape.
     if (!grepl(check_regex, check_line) && !grepl("NOCHECK", check_line, fixed=TRUE)) {
-      bad_lines_idx <- seq(alloc_lines[grp_idx[1L]], length.out=length(grp_idx)+1L)
-      cat("FILE: ", c_file, "; LINES: ", head(bad_lines_idx, 1L), "-", tail(bad_lines_idx, 1L), "\n", sep="")
+      bad_lines_idx = seq(alloc_lines[grp_idx[1L]], length.out=length(grp_idx)+1L)
+      cat("FILE: ", c_obj$path, "; LINES: ", head(bad_lines_idx, 1L), "-", tail(bad_lines_idx, 1L), "\n", sep="")
       writeLines(lines[bad_lines_idx])
       cat(strrep("-", max(nchar(lines[bad_lines_idx]))), "\n", sep="")
       stop("Expected the malloc()/calloc() usage above to be followed immediately by error checking.", call.=FALSE)

.ci/linters/c/omp_set_num_threads_linter.R

@@ -1,13 +1,11 @@
-
 # Ensure no calls to omp_set_num_threads() [to avoid affecting other packages and base R]
 # Only comments referring to it should be in openmp-utils.c
-omp_set_num_threads_linter = function(c_file) {
+omp_set_num_threads_linter = function(c_obj) {
   # strip comments, we only care if the function appears in actual code.
-  processed_lines = system2("gcc", c("-fpreprocessed", "-E", c_file), stdout=TRUE, stderr=FALSE)
-  idx = grep("omp_set_num_threads", processed_lines, fixed = TRUE)
+  idx = grep("omp_set_num_threads", c_obj$preprocessed, fixed = TRUE)
   if (!length(idx)) return()
   stop(sprintf(
     "In %s, found omp_set_num_threads() usage, which could affect other packages and base R:\n%s",
-    c_file, paste0("  ", format(idx), ":", processed_lines[idx], collapse = "\n")
+    c_obj$path, paste0("  ", format(idx), ":", c_obj$preprocessed[idx], collapse = "\n")
   ))
 }

.github/workflows/code-quality.yaml

@@ -43,7 +43,9 @@ jobs:
           linter_env = new.env()
           for (f in list.files('.ci/linters/c', full.names=TRUE)) sys.source(f, linter_env)
           for (f in list.files('src', pattern='[.][ch]$', full.names=TRUE)) {
-            for (linter in ls(linter_env)) linter_env[[linter]](f)
+            c_obj = list(path = f, lines = readLines(f))
+            c_obj$preprocessed = system2("gcc", c("-fpreprocessed", "-E", f), stdout=TRUE, stderr=FALSE)
+            for (linter in ls(linter_env)) linter_env[[linter]](c_obj)
             # TODO(#6272): Incorporate more checks from CRAN_Release
           }
         shell: Rscript {0}