Fix fread crashes (#5046)

NEWS.md

@@ -137,6 +137,9 @@
 
 21. `melt()` on a `data.table` with `list` columns for `measure.vars` would silently ignore `na.rm=TRUE`, [#5044](https://github.com/Rdatatable/data.table/issues/5044). Now the same logic as `is.na()` from base R is used; i.e. if list element is scalar NA then it is considered missing and removed. Thanks to Toby Dylan Hocking for the PRs.
 
+22. `fread(fill=TRUE)` could segfault if the input contained an improperly quoted character field, [#4774](https://github.com/Rdatatable/data.table/issues/4774) [#5041](https://github.com/Rdatatable/data.table/issues/5041). Thanks to @AndeolEvain and @e-nascimento for reporting and to Václav Tlapák for the PR.
+
+23. `fread(fill=TRUE, verbose=TRUE)` would segfault on the out-of-sample type bump verbose output if the input did not contain column names, [5046](https://github.com/Rdatatable/data.table/pull/5046). Thanks to Václav Tlapák for the PR.
 
 ## NOTES
 

inst/tests/tests.Rraw

@@ -17763,3 +17763,15 @@ test(2195.5, duplicated(DT, by=character(0L)), ans<-c(FALSE, FALSE, TRUE, FALSE)
 test(2195.6, duplicated(DT, by=NULL), ans)
 test(2195.7, anyDuplicated(DT, by=character(0L)), 3L)
 test(2195.8, anyDuplicated(DT, by=NULL), 3L)
+
+# Improperly quoted character field with fill=TRUE would segfault, #4774 and #5041
+test(2196,
+     fread(paste0(paste(rep(c('a; b'), 100), collapse='\n'), c('\n"a" 2;b')), fill=TRUE, quote='\"'),
+     data.table(a=c(rep('a', 99), '"a" 2'), b=rep('b', 100)), warning='Found and resolved improper quoting')
+
+# Verbose output would segfault when no header present, out-of-sample type error and fill=TRUE, similar to #4644
+# Test vaildity may depend on sampling behaviour of fread since the type bump needs to occur out of sample to trigger the segfault
+sampleText = paste0(paste(rep(c('1; 2'), 100), collapse='\n'), c('\n"a";2\n1; 2\n'), paste(rep(c('1; 2'), 100), collapse='\n'))
+test(2197, fread(sampleText, fill=TRUE, quote='\"', verbose=TRUE, header=FALSE),
+           data.table(rep(c("1","a","1"),c(100,1,101)), 2L),
+           output='Column 1 bumped')

src/fread.c

@@ -2361,6 +2361,9 @@ int freadMain(freadMainArgs _args) {
               if (j+fieldsRemaining != ncol) break;
               checkedNumberOfFields = true;
             }
+            if (thisType <= -NUMTYPE) {
+              break;  // Improperly quoted char field needs to be healed below, other columns will be filled #5041 and #4774
+            }
             #pragma omp critical
             {
               joldType = type[j];  // fetch shared value again in case another thread bumped it while I was waiting.
@@ -2369,8 +2372,8 @@ int freadMain(freadMainArgs _args) {
                 if (verbose) {
                   char temp[1001];
                   int len = snprintf(temp, 1000,
-                    _("Column %d (\"%.*s\") bumped from '%s' to '%s' due to <<%.*s>> on row %"PRIu64"\n"),
-                    j+1, colNames[j].len, colNamesAnchor + colNames[j].off,
+                    _("Column %d%s%.*s%s bumped from '%s' to '%s' due to <<%.*s>> on row %"PRIu64"\n"),
+                    j+1, colNames?" <<":"", colNames?(colNames[j].len):0, colNames?(colNamesAnchor+colNames[j].off):"", colNames?">>":"",
                     typeName[abs(joldType)], typeName[abs(thisType)],
                     (int)(tch-fieldStart), fieldStart, (uint64_t)(ctx.DTi+myNrow));
                   if (len > 1000) len = 1000;