use let-else syntax where possible (#8886)

# Description
this pr changes some `if-let`s to `let-else`s

# User-Facing Changes
none

crates/nu-cmd-lang/src/core_commands/help_aliases.rs

@@ -111,15 +111,13 @@ pub fn help_aliases(
             name.push_str(&r.item);
         }
 
-        let alias = if let Some(id) = engine_state.find_decl(name.as_bytes(), &[]) {
-            if let Some(alias) = engine_state.get_decl(id).as_alias() {
-                alias
-            } else {
-                return Err(ShellError::AliasNotFound(span(
-                    &rest.iter().map(|r| r.span).collect::<Vec<Span>>(),
-                )));
-            }
-        } else {
+        let Some(alias) = engine_state.find_decl(name.as_bytes(), &[]) else {
+            return Err(ShellError::AliasNotFound(span(
+                &rest.iter().map(|r| r.span).collect::<Vec<Span>>(),
+            )));
+        };
+
+        let Some(alias) = engine_state.get_decl(alias).as_alias() else {
             return Err(ShellError::AliasNotFound(span(
                 &rest.iter().map(|r| r.span).collect::<Vec<Span>>(),
             )));

crates/nu-cmd-lang/src/core_commands/help_modules.rs

@@ -117,9 +117,7 @@ pub fn help_modules(
             name.push_str(&r.item);
         }
 
-        let module_id = if let Some(id) = engine_state.find_module(name.as_bytes(), &[]) {
-            id
-        } else {
+        let Some(module_id) = engine_state.find_module(name.as_bytes(), &[]) else {
             return Err(ShellError::ModuleNotFoundAtRuntime {
                 mod_name: name,
                 span: span(&rest.iter().map(|r| r.span).collect::<Vec<Span>>()),

crates/nu-cmd-lang/src/core_commands/use_.rs

@@ -45,13 +45,10 @@ impl Command for Use {
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        let import_pattern = if let Some(Expression {
-            expr: Expr::ImportPattern(pat),
+        let Some(Expression {
+            expr: Expr::ImportPattern(import_pattern),
             ..
-        }) = call.get_parser_info("import_pattern")
-        {
-            pat
-        } else {
+        }) = call.get_parser_info("import_pattern") else {
             return Err(ShellError::GenericError(
                 "Unexpected import".into(),
                 "import pattern not supported".into(),

crates/nu-engine/src/column.rs

@@ -5,14 +5,14 @@ pub fn get_columns<'a>(input: impl IntoIterator<Item = &'a Value>) -> Vec<String
     let mut columns = vec![];
 
     for item in input {
-        if let Value::Record { cols, .. } = item {
-            for col in cols {
-                if !columns.contains(col) {
-                    columns.push(col.to_string());
-                }
-            }
-        } else {
+        let Value::Record { cols, .. } = item else {
             return vec![];
+        };
+
+        for col in cols {
+            if !columns.contains(col) {
+                columns.push(col.to_string());
+            }
         }
     }
 

crates/nu-parser/src/parse_keywords.rs

@@ -669,9 +669,7 @@ pub fn parse_alias(
             return alias_pipeline;
         }
 
-        let alias_name_expr = if let Some(expr) = alias_call.positional_nth(0) {
-            expr
-        } else {
+        let Some(alias_name_expr) = alias_call.positional_nth(0) else {
             working_set.error(ParseError::UnknownState(
                 "Missing positional after call check".to_string(),
                 span(spans),
@@ -932,9 +930,7 @@ pub fn parse_export_in_module(
         return (garbage_pipeline(spans), vec![]);
     };
 
-    let export_decl_id = if let Some(id) = working_set.find_decl(b"export", &Type::Any) {
-        id
-    } else {
+    let Some(export_decl_id) = working_set.find_decl(b"export", &Type::Any) else {
         working_set.error(ParseError::InternalError(
             "missing export command".into(),
             export_span,

crates/nu-parser/src/parser.rs

@@ -2880,9 +2880,7 @@ pub fn parse_type(_working_set: &StateWorkingSet, bytes: &[u8]) -> Type {
 }
 
 pub fn parse_import_pattern(working_set: &mut StateWorkingSet, spans: &[Span]) -> Expression {
-    let head_span = if let Some(head_span) = spans.get(0) {
-        head_span
-    } else {
+    let Some(head_span) = spans.get(0) else {
         working_set.error(ParseError::WrongImportPattern(span(spans)));
         return garbage(span(spans));
     };

crates/nu-protocol/src/value/range.rs

@@ -213,9 +213,7 @@ impl Iterator for RangeIterator {
             self.curr.partial_cmp(&self.end)
         };
 
-        let ordering = if let Some(ord) = ordering {
-            ord
-        } else {
+        let Some(ordering) = ordering  else {
             self.done = true;
             return Some(Value::Error {
                 error: Box::new(ShellError::CannotCreateRange { span: self.span }),