revsets: allow spaces in most places (but not after prefix operators)

lib/src/revset.pest

@@ -14,6 +14,7 @@
 
 symbol = @{ (ASCII_ALPHANUMERIC | "@" | "/" | ".")+ }
 literal_string = { "\"" ~ (!"\"" ~ ANY)+ ~ "\"" }
+whitespace = _{ " " }
 
 parents = { ":" }
 ancestors = { "*:" }
@@ -35,8 +36,8 @@ function_argument = {
   | expression
 }
 function_arguments = {
-  (function_argument ~ ",")* ~ function_argument
+  (whitespace* ~ function_argument ~ whitespace* ~ ",")* ~ whitespace* ~ function_argument ~ whitespace*
-  | ""
+  | whitespace*
 }
 
 primary = {
@@ -48,9 +49,9 @@ primary = {
 prefix_expression = { prefix_operator* ~ primary }
 
 infix_expression = {
-  prefix_expression ~ (infix_operator ~ prefix_expression)*
+  whitespace* ~ prefix_expression ~ whitespace* ~ (infix_operator ~ whitespace* ~ prefix_expression ~ whitespace*)*
 }
 
 expression = {
-  infix_expression
+  whitespace* ~ infix_expression ~ whitespace*
 }

lib/src/revset.rs

@@ -343,6 +343,8 @@ fn parse_function_argument_to_string(
 }
 
 pub fn parse(revset_str: &str) -> Result<RevsetExpression, RevsetParseError> {
+    // TODO: Return a better error message when parsing fails (such as when the user
+    // puts whitespace between a prefix operator and the operand)
     let mut pairs: Pairs<Rule> = RevsetParser::parse(Rule::expression, revset_str).unwrap();
     let first = pairs.next().unwrap();
     assert!(pairs.next().is_none());

lib/tests/test_revset.rs

@@ -255,6 +255,27 @@ fn test_parse_revset() {
             RevsetExpression::Symbol("@".to_string())
         )))
     );
+    assert_eq!(
+        parse(" *:@ "),
+        Ok(RevsetExpression::Ancestors(Box::new(
+            RevsetExpression::Symbol("@".to_string())
+        )))
+    );
+    assert_eq!(
+        parse("   description(  arg1 ,   arg2 ) -    parents(   arg1  )  - all_heads(  )  "),
+        Ok(RevsetExpression::Difference(
+            Box::new(RevsetExpression::Difference(
+                Box::new(RevsetExpression::Description {
+                    needle: "arg1".to_string(),
+                    base_expression: Box::new(RevsetExpression::Symbol("arg2".to_string()))
+                }),
+                Box::new(RevsetExpression::Parents(Box::new(
+                    RevsetExpression::Symbol("arg1".to_string())
+                )))
+            )),
+            Box::new(RevsetExpression::AllHeads)
+        ))
+    );
 }
 
 #[test]