Use regexp for case-insensitive literal matches

This commit switches back to using the regexp engine for
case-insensitive literal string matches.

This is slower, but at least case-insensitive matches for string
literals will function now. The code is a tiny bit shorter and simpler
too.

Given the aim of the tool is to be useful for ad-hoc searches,
efficiency isn't the concern but rather just getting the job done with
the minimum of fuss / unexpected behaviour.

file.go

@@ -274,12 +274,6 @@ func findMatches(data []byte) (loc []int) {
 			return loc
 		}
 	}
-	for _, s := range searchBytes {
-		pos := bytes.Index(data, s)
-		if pos != -1 {
-			return []int{pos, pos + len(s)}
-		}
-	}
 	return nil
 }
 

main.go

@@ -17,7 +17,6 @@ import (
 )
 
 // TODO:
-//  - it would be better to make fixed patterns case insensitive too.
 //  - configurable defaults for exclude.
 
 func main() {
@@ -42,10 +41,9 @@ which can be repeated multiple times. -e specifies a regular expression and
 -Q a fixed pattern. When using either flag, any non-flag arguments are treated
 as paths to scan.
 
-Search defaults to case-sensitive but the -i flag may be passed to make regular
-expression searches case-insensitive. Alternatively, the "(?i)" construct may be
-added to a regular expression to make that specific expression case insensitive.
-Fixed pattern matches are always case-sensitive.
+Search defaults to case-sensitive but the -i flag may be passed to make all
+search terms case-insensitive. Alternatively, the "(?i)" construct may be added
+to a regular expression to make that specific expression case insensitive.
 
 Files and directories can be excluded with the -x option. This supports bash-style
 globs with '*', '?', '[a-z]', '{this,that}', or '/**/' to match zero or more
@@ -58,7 +56,6 @@ var (
 	searchRegexp []string
 	regexps      []*regexp.Regexp
 	searchFixed  []string
-	searchBytes  [][]byte
 	searchPath   []string
 	excludeList  []string
 	binaryFile   notPlainTextFlag
@@ -116,8 +113,15 @@ func run(c *cobra.Command, args []string) error {
 		regexps = append(regexps, re)
 	}
 
-	for _, s := range searchFixed {
-		searchBytes = append(searchBytes, []byte(s))
+	for _, r := range searchFixed {
+		r = regexp.QuoteMeta(r)
+		if ignoreCase {
+			r = "(?i)" + r
+		}
+		re, err := regexp.Compile(r)
+		if err != nil {
+		}
+		regexps = append(regexps, re)
 	}
 
 	var errs []error