Add --smart-case.

It does what it says on the tin.

Closes BurntSushi#70.

doc/rg.1

@@ -238,6 +238,12 @@ Alias for \-\-color=always \-\-heading \-n.
 .RS
 .RE
 .TP
+.B \-S, \-\-smart\-case
+Search case insensitively if the pattern is all lowercase.
+Search case sensitively otherwise.
+.RS
+.RE
+.TP
 .B \-j, \-\-threads \f[I]ARG\f[]
 The number of threads to use.
 Defaults to the number of logical CPUs (capped at 6).

doc/rg.1.md

@@ -154,6 +154,10 @@ the raw speed of grep.
 -p, --pretty
 : Alias for --color=always --heading -n.
 
+-S, --smart-case
+: Search case insensitively if the pattern is all lowercase.
+  Search case sensitively otherwise.
+
 -j, --threads *ARG*
 : The number of threads to use. Defaults to the number of logical CPUs
   (capped at 6). [default: 0]

grep/src/search.rs

@@ -52,6 +52,7 @@ pub struct GrepBuilder {
 #[derive(Clone, Debug)]
 struct Options {
     case_insensitive: bool,
+    case_smart: bool,
     line_terminator: u8,
     size_limit: usize,
     dfa_size_limit: usize,
@@ -61,6 +62,7 @@ impl Default for Options {
     fn default() -> Options {
         Options {
             case_insensitive: false,
+            case_smart: false,
             line_terminator: b'\n',
             size_limit: 10 * (1 << 20),
             dfa_size_limit: 10 * (1 << 20),
@@ -98,6 +100,18 @@ impl GrepBuilder {
         self
     }
 
+    /// Whether to enable smart case search or not (disabled by default).
+    ///
+    /// Smart case uses case insensitive search if the regex is contains all
+    /// lowercase literal characters. Otherwise, a case sensitive search is
+    /// used instead.
+    ///
+    /// Enabling the case_insensitive flag overrides this.
+    pub fn case_smart(mut self, yes: bool) -> GrepBuilder {
+        self.opts.case_smart = yes;
+        self
+    }
+
     /// Set the approximate size limit of the compiled regular expression.
     ///
     /// This roughly corresponds to the number of bytes occupied by a
@@ -148,8 +162,11 @@ impl GrepBuilder {
     /// Creates a new regex from the given expression with the current
     /// configuration.
     fn regex(&self, expr: &Expr) -> Result<Regex> {
+        let casei =
+            self.opts.case_insensitive
+            || (self.opts.case_smart && !has_uppercase_literal(expr));
         RegexBuilder::new(&expr.to_string())
-            .case_insensitive(self.opts.case_insensitive)
+            .case_insensitive(casei)
             .multi_line(true)
             .unicode(true)
             .size_limit(self.opts.size_limit)
@@ -274,6 +291,23 @@ impl<'b, 's> Iterator for Iter<'b, 's> {
     }
 }
 
+fn has_uppercase_literal(expr: &Expr) -> bool {
+    use syntax::Expr::*;
+    match *expr {
+        Literal { ref chars, casei } => {
+            casei || chars.iter().any(|c| c.is_uppercase())
+        }
+        LiteralBytes { ref bytes, casei } => {
+            casei || bytes.iter().any(|&b| b'A' <= b && b <= b'Z')
+        }
+        Group { ref e, .. } => has_uppercase_literal(e),
+        Repeat { ref e, .. } => has_uppercase_literal(e),
+        Concat(ref es) => es.iter().any(has_uppercase_literal),
+        Alternate(ref es) => es.iter().any(has_uppercase_literal),
+        _ => false,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     #![allow(unused_imports)]

src/args.rs

@@ -154,6 +154,10 @@ Less common options:
     -p, --pretty
         Alias for --color=always --heading -n.
 
+    -S, --smart-case
+        Search case insensitively if the pattern is all lowercase.
+        Search case sensitively otherwise.
+
     -j, --threads ARG
         The number of threads to use. Defaults to the number of logical CPUs
         (capped at 6). [default: 0]
@@ -217,6 +221,7 @@ pub struct RawArgs {
     flag_quiet: bool,
     flag_regexp: Vec<String>,
     flag_replace: Option<String>,
+    flag_smart_case: bool,
     flag_text: bool,
     flag_threads: usize,
     flag_type: Vec<String>,
@@ -348,6 +353,7 @@ impl RawArgs {
         let types = try!(btypes.build());
         let grep = try!(
             GrepBuilder::new(&pattern)
+                .case_smart(self.flag_smart_case)
                 .case_insensitive(self.flag_ignore_case)
                 .line_terminator(eol)
                 .build()

tests/tests.rs

@@ -699,6 +699,18 @@ clean!(feature_68, "test", ".", |wd: WorkDir, mut cmd: Command| {
     assert_eq!(lines, "foo:test\n");
 });
 
+// See: https://github.com/BurntSushi/ripgrep/issues/70
+sherlock!(feature_70, "sherlock", ".", |wd: WorkDir, mut cmd: Command| {
+    cmd.arg("--smart-case");
+
+    let lines: String = wd.stdout(&mut cmd);
+    let expected = "\
+sherlock:For the Doctor Watsons of this world, as opposed to the Sherlock
+sherlock:be, to a very large extent, the result of luck. Sherlock Holmes
+";
+    assert_eq!(lines, expected);
+});
+
 #[test]
 fn binary_nosearch() {
     let wd = WorkDir::new("binary_nosearch");