Make Polonius report any found errors by default

It's a bit confusing that running Polonius on some Rust code that you
know has a borrow error doesn't seem to actually do anything - it gives
the impression that no analysis is performed by default.

Of course, analysis *is* performed by default, but errors aren't
reported unless you opt in (which begs the question of what exactly the
tool is meant to be doing when you run it!)

This changes the behaviour to print error tuples by default if any are
found, for a better experience. The old behaviour can be re-enabled by
using `--no-show-tuples` to suppress tuple output even if errors are
present.

README.md

@@ -34,10 +34,10 @@ slower) -- these are the exact rules described in [the
 blogpost][post]. You can also use `-a LocationInsensitive` to use a
 location insensitive analysis (faster, but may yield spurious errors).
 
-By default, `cargo run` just prints timing. If you also want to see
-the results, try `--show-tuples` (which will show errors) and maybe
-`-v` (to show more intermediate computations). You can supply `--help`
-to get more docs.
+By default, `cargo run` will print any errors found, but otherwise
+just prints timing. If you also want to see successful results, try
+`--show-tuples` and maybe `-v` (to show more intermediate computations).
+You can supply `--help` to get more docs.
 
 ### How to generate your own inputs
 

book/src/getting_started.md

@@ -19,9 +19,9 @@ slower) -- these are the exact rules described in [the
 blogpost][post]. You can also use `-a LocationInsensitive` to use a
 location insensitive analysis (faster, but may yield spurious errors).
 
-By default, `cargo run` just prints timing. If you also want to see
-the results, try `--show-tuples` (which will show errors) and maybe
-`-v` (to show more intermediate computations). You can supply `--help`
-to get more docs.
+By default, `cargo run` will print any errors found, but otherwise
+just prints timing. If you also want to see successful results, try
+`--show-tuples` and maybe `-v` (to show more intermediate computations).
+You can supply `--help` to get more docs.
 
 [post]: http://smallcultfollowing.com/babysteps/blog/2018/04/27/an-alias-based-formulation-of-the-borrow-checker/

polonius-engine/src/output/mod.rs

@@ -514,6 +514,10 @@ impl<T: FactTypes> Output<T> {
             None => Cow::Owned(BTreeMap::default()),
         }
     }
+
+    pub fn has_errors(&self) -> bool {
+        !(self.errors.is_empty() && self.move_errors.is_empty() && self.subset_errors.is_empty())
+    }
 }
 
 /// Compares errors reported by Naive implementation with the errors

src/cli.rs

@@ -22,7 +22,7 @@ const PKG_DESCRIPTION: &str = env!("CARGO_PKG_DESCRIPTION");
 #[derive(Debug)]
 pub struct Options {
     algorithm: Algorithm,
-    show_tuples: bool,
+    show_tuples: Option<bool>,
     skip_timing: bool,
     verbose: bool,
     graphviz_file: Option<String>,
@@ -81,7 +81,7 @@ pub fn main(opt: Options) -> Result<(), Error> {
                     let millis = f64::from(duration.subsec_nanos()) * 0.000_000_001_f64;
                     println!("Time: {:0.3}s", seconds + millis);
                 }
-                if opt.show_tuples {
+                if opt.show_tuples.unwrap_or_else(|| output.has_errors()) {
                     dump::dump_output(&output, &output_directory, tables)
                         .expect("Failed to write output");
                 }
@@ -131,11 +131,11 @@ USAGE:
     polonius [FLAGS] [OPTIONS] <fact_dirs>...
 
 FLAGS:
-    -h, --help           Prints help information
-        --show-tuples    Show output tuples on stdout
-        --skip-timing    Do not display timing results
-    -V, --version        Prints version information
-    -v, --verbose        Show intermediate output tuples and not just errors
+    -h, --help                Prints help information
+        --[no-]show-tuples    Show output tuples on stdout, or suppress errors
+        --skip-timing         Do not display timing results
+    -V, --version             Prints version information
+    -v, --verbose             Show intermediate output tuples and not just errors
 
 OPTIONS:
     -a <algorithm> [default: Naive]
@@ -163,7 +163,13 @@ ARGS:
     // 2) parse args
     let options = Options {
         algorithm: arg_from_str(&mut args, "-a")?.unwrap_or(Algorithm::Naive),
-        show_tuples: args.contains("--show-tuples"),
+        show_tuples: if args.contains("--show-tuples") {
+            Some(true)
+        } else if args.contains("--no-show-tuples") {
+            Some(false)
+        } else {
+            None
+        },
         skip_timing: args.contains("--skip-timing"),
         verbose: args.contains(["-v", "--verbose"]),
         graphviz_file: arg_from_str(&mut args, "--graphviz-file")?,