clippy: turn on map_unwrap_or lint

Style.

This one looks a bit scary because it's not obvious what the right order
of parameters to `map_or` is, but actually it's fine -- the first
parameter is an object and the second is a function, and they only look
the same because of Rust's pattern syntax.

Author: apoelstra

Cargo.toml

@@ -107,7 +107,7 @@ manual_let_else = "warn"
 manual_ok_or = "warn"
 manual_string_new = "warn"
 many_single_char_names = "warn"
-map_unwrap_or = "allow"
+map_unwrap_or = "warn"
 match_wild_err_arm = "warn"
 match_wildcard_for_single_variants = "allow"
 maybe_infinite_iter = "warn"

src/compile.rs

@@ -617,8 +617,7 @@ impl Match {
                 .pattern()
                 .as_variable()
                 .cloned()
-                .map(Pattern::Identifier)
-                .unwrap_or(Pattern::Ignore),
+                .map_or(Pattern::Ignore, Pattern::Identifier),
         );
         let left = self.left().expression().compile(scope)?;
         scope.pop_scope();
@@ -629,8 +628,7 @@ impl Match {
                 .pattern()
                 .as_variable()
                 .cloned()
-                .map(Pattern::Identifier)
-                .unwrap_or(Pattern::Ignore),
+                .map_or(Pattern::Ignore, Pattern::Identifier),
         );
         let right = self.right().expression().compile(scope)?;
         scope.pop_scope();

src/error.rs

@@ -233,7 +233,7 @@ impl fmt::Display for RichError {
                 writeln!(f, "{:width$} |", " ", width = line_num_width)?;
 
                 let mut lines = file.lines().skip(start_line_index).peekable();
-                let start_line_len = lines.peek().map(|l| l.len()).unwrap_or(0);
+                let start_line_len = lines.peek().map_or(0, |l| l.len());
 
                 for (relative_line_index, line_str) in lines.take(n_spanned_lines).enumerate() {
                     let line_num = start_line_index + relative_line_index + 1;