clippy: invert != in if statements

This is a stylistic lint which you could argue either way, but I like
having it on for consistency.

Author: apoelstra

Cargo.toml

@@ -77,7 +77,7 @@ flat_map_option = "warn"
 float_cmp = "warn"
 fn_params_excessive_bools = "warn"
 from_iter_instead_of_collect = "warn"
-if_not_else = "allow"
+if_not_else = "warn"
 ignored_unit_patterns = "allow"
 implicit_clone = "warn"
 implicit_hasher = "warn"

src/ast.rs

@@ -1039,27 +1039,27 @@ impl AbstractSyntaxTree for Call {
             parse_args: &[parse::Expression],
             expected_tys: &[ResolvedType],
         ) -> Result<(), Error> {
-            if parse_args.len() != expected_tys.len() {
+            if parse_args.len() == expected_tys.len() {
+                Ok(())
+            } else {
                 Err(Error::InvalidNumberOfArguments(
                     expected_tys.len(),
                     parse_args.len(),
                 ))
-            } else {
-                Ok(())
             }
         }
 
         fn check_output_type(
             observed_ty: &ResolvedType,
             expected_ty: &ResolvedType,
         ) -> Result<(), Error> {
-            if observed_ty != expected_ty {
+            if observed_ty == expected_ty {
+                Ok(())
+            } else {
                 Err(Error::ExpressionTypeMismatch(
                     expected_ty.clone(),
                     observed_ty.clone(),
                 ))
-            } else {
-                Ok(())
             }
         }