Flip the new/old order, and add suggestion for -lt

I changed my mind about which way round sorting by “newest” or by “oldest” should actually go. If you’re listing a large directory, you see the last lines of the output first, so these files should be the ones with the largest whatever the sort field is. It’s about sorting *last*, not sorting *first*. Sorting by size wouldn’t say “sorts smallest files first”, it would say “sorts largest files last”. Right?

Also, add a new suggestion that warns against “ls -lt”.

7 files changed, 32 insertions, 12 deletions

diff --git a/README.md b/README.md
index 919a986..70ef9b5 100644
--- a/README.md
+++ b/README.md
@@ -54,7 +54,7 @@ These options are available when running with --long (`-l`):
 - **--time-style**: how to format timestamps
 
 - Valid **--color** options are **always**, **automatic**, and **never**.
-- Valid sort fields are **accessed**, **created**, **extension**, **Extension**, **inode**, **modified**, **name**, **Name**, **size**, **type**, and **none**. Fields starting with a capital letter sort uppercase before lowercase. The modified field has the aliases **date**, **time**, and **oldest**, while its reverse has the aliases **age** and **newest**.
+- Valid sort fields are **accessed**, **created**, **extension**, **Extension**, **inode**, **modified**, **name**, **Name**, **size**, **type**, and **none**. Fields starting with a capital letter sort uppercase before lowercase. The modified field has the aliases **date**, **time**, and **newest**, while its reverse has the aliases **age** and **oldest**.
 - Valid time fields are **modified**, **accessed**, and **created**.
 - Valid time styles are **default**, **iso**, **long-iso**, and **full-iso**.
 
diff --git a/contrib/man/exa.1 b/contrib/man/exa.1
index fb201e8..dadb6c4 100644
--- a/contrib/man/exa.1
+++ b/contrib/man/exa.1
@@ -77,7 +77,7 @@ reverse the sort order
 .B \-s, \-\-sort=\f[I]SORT_FIELD\f[]
 which field to sort by.
 Valid fields are name, Name, extension, Extension, size, modified, accessed, created, inode, type, and none.
-The modified field has the aliases date, time, and oldest, and its reverse order has the aliases age and newest.
+The modified field has the aliases date, time, and newest, and its reverse order has the aliases age and oldest.
 Fields starting with a capital letter will sort uppercase before lowercase: 'A' then 'B' then 'a' then 'b'.
 Fields starting with a lowercase letter will mix them: 'A' then 'a' then 'B' then 'b'.
 .RS
diff --git a/src/options/filter.rs b/src/options/filter.rs
index 6d4b2f5..6ed2a4e 100644
--- a/src/options/filter.rs
+++ b/src/options/filter.rs
@@ -49,10 +49,17 @@ impl SortField {
         else if word == "Ext" || word == "Extension" {
             Ok(SortField::Extension(SortCase::ABCabc))
         }
-        else if word == "date" || word == "time" || word == "mod" || word == "modified" || word == "old" || word == "oldest" {
+        else if word == "date" || word == "time" || word == "mod" || word == "modified" || word == "new" || word == "newest" {
+            // “new” sorts oldest at the top and newest at the bottom; “old”
+            // sorts newest at the top and oldest at the bottom. I think this
+            // is the right way round to do this: “size” puts the smallest at
+            // the top and the largest at the bottom, doesn’t it?
             Ok(SortField::ModifiedDate)
         }
-        else if word == "age" || word == "new" || word == "newest" {
+        else if word == "age" || word == "old" || word == "oldest" {
+            // Similarly, “age” means that files with the least age (the
+            // newest files) get sorted at the top, and files with the most
+            // age (the oldest) at the bottom.
             Ok(SortField::ModifiedAge)
         }
         else if word == "acc" || word == "accessed" {
@@ -209,10 +216,10 @@ mod test {
         test!(one_short:     SortField <- ["-saccessed"];      Both => Ok(SortField::AccessedDate));
         test!(lowercase:     SortField <- ["--sort", "name"];  Both => Ok(SortField::Name(SortCase::AaBbCc)));
         test!(uppercase:     SortField <- ["--sort", "Name"];  Both => Ok(SortField::Name(SortCase::ABCabc)));
-        test!(old:           SortField <- ["--sort", "old"];   Both => Ok(SortField::ModifiedDate));
-        test!(oldest:        SortField <- ["--sort=oldest"];   Both => Ok(SortField::ModifiedDate));
-        test!(new:           SortField <- ["--sort", "new"];   Both => Ok(SortField::ModifiedAge));
-        test!(newest:        SortField <- ["--sort=newest"];   Both => Ok(SortField::ModifiedAge));
+        test!(old:           SortField <- ["--sort", "new"];   Both => Ok(SortField::ModifiedDate));
+        test!(oldest:        SortField <- ["--sort=newest"];   Both => Ok(SortField::ModifiedDate));
+        test!(new:           SortField <- ["--sort", "old"];   Both => Ok(SortField::ModifiedAge));
+        test!(newest:        SortField <- ["--sort=oldest"];   Both => Ok(SortField::ModifiedAge));
         test!(age:           SortField <- ["-sage"];           Both => Ok(SortField::ModifiedAge));
 
         // Errors
diff --git a/src/options/misfire.rs b/src/options/misfire.rs
index 58c1ef4..5cc0ba3 100644
--- a/src/options/misfire.rs
+++ b/src/options/misfire.rs
@@ -113,10 +113,19 @@ impl fmt::Display for ParseError {
 }
 
 impl Misfire {
+    /// Try to second-guess what the user was trying to do, depending on what
+    /// went wrong.
     pub fn suggestion(&self) -> Option<&'static str> {
+        // ‘ls -lt’ and ‘ls -ltr’ are common combinations
         if let Misfire::BadArgument(ref time, ref r) = *self {
             if *time == &flags::TIME && r == "r" {
-                return Some("To sort newest files first, try \"--sort modified\", or just \"-stime\"");
+                return Some("To sort oldest files last, try \"--sort oldest\", or just \"-sold\"");
+            }
+        }
+
+        if let Misfire::InvalidOptions(ParseError::NeedsValue { ref flag, values: _ }) = *self {
+            if *flag == Flag::Short(b't') {
+                return Some("To sort newest files last, try \"--sort newest\", or just \"-snew\"");
             }
         }
 
diff --git a/xtests/error_lt b/xtests/error_lt
new file mode 100644
index 0000000..33f239a
--- /dev/null
+++ b/xtests/error_lt
@@ -0,0 +1,2 @@
+Flag -t needs a value (choices: modified, accessed, created)
+To sort newest files last, try "--sort newest", or just "-snew"
diff --git a/xtests/error_ltr b/xtests/error_ltr
index 84bbe47..b2f3c54 100644
--- a/xtests/error_ltr
+++ b/xtests/error_ltr
@@ -1,2 +1,2 @@
 Option --time (-t) has no "r" setting (choices: modified, accessed, created)
-To sort newest files first, try "--sort modified", or just "-stime"
+To sort oldest files last, try "--sort oldest", or just "-sold"
diff --git a/xtests/run.sh b/xtests/run.sh
index e2164ed..b88ae20 100755
--- a/xtests/run.sh
+++ b/xtests/run.sh
@@ -143,8 +143,9 @@ $exa $testcases/file-names-exts/music.* -I "*.OGG|*.mp3" -1 2>&1 | diff -q - $re
 # Dates and times
 $exa $testcases/dates -lh --accessed --sort=accessed 2>&1 | diff -q - $results/dates_accessed  || exit 1
 $exa $testcases/dates -lh            --sort=modified 2>&1 | diff -q - $results/dates_modified  || exit 1
-$exa $testcases/dates -lh         -r --sort=newest   2>&1 | diff -q - $results/dates_modified  || exit 1
-$exa $testcases/dates -lh            --sort=newest   2>&1 | diff -q - $results/dates_deifidom  || exit 1
+$exa $testcases/dates -lh            --sort=newest   2>&1 | diff -q - $results/dates_modified  || exit 1
+$exa $testcases/dates -lh         -r --sort=newest   2>&1 | diff -q - $results/dates_deifidom  || exit 1
+$exa $testcases/dates -lh            --sort=oldest   2>&1 | diff -q - $results/dates_deifidom  || exit 1
 $exa $testcases/dates -l       --time-style=long-iso 2>&1 | diff -q - $results/dates_long_iso  || exit 1
 $exa $testcases/dates -l       --time-style=full-iso 2>&1 | diff -q - $results/dates_full_iso  || exit 1
 $exa $testcases/dates -l       --time-style=iso      2>&1 | diff -q - $results/dates_iso       || exit 1
@@ -265,6 +266,7 @@ $exa -l --time-style=24 2>&1 | diff -q - $results/error_setting     || exit 1
 
 # Error suggestions
 $exa -ltr 2>&1 | diff -q - $results/error_ltr  || exit 1
+$exa -lt  2>&1 | diff -q - $results/error_lt   || exit 1
 
 
 # Debug mode