From 5709cf031ba00ce8eb330a9a72ed0f572d591bcd Mon Sep 17 00:00:00 2001
From: Tad Hardesty <tad@platymuus.com>
Date: Sun, 8 Dec 2019 00:29:39 -0800
Subject: [PATCH] Add parse_expression convenience function

---
 src/dreammaker/constants.rs    |  3 +--
 src/dreammaker/parser.rs       | 17 +++++++++++++++--
 src/dreammaker/preprocessor.rs |  9 ++++-----
 3 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/src/dreammaker/constants.rs b/src/dreammaker/constants.rs
index 6241abcb..b3cfb37f 100644
--- a/src/dreammaker/constants.rs
+++ b/src/dreammaker/constants.rs
@@ -391,11 +391,10 @@ impl fmt::Display for ConstFn {
 
 pub fn evaluate_str(location: Location, input: &[u8]) -> Result<Constant, DMError> {
     use super::lexer::{Lexer, from_utf8_or_latin1_borrowed};
-    use super::parser::Parser;
 
     let mut bytes = input.iter().map(|&x| Ok(x));
     let ctx = Context::default();
-    let expr = Parser::new(&ctx, Lexer::new(&ctx, Default::default(), &mut bytes)).require_expression()?;
+    let expr = crate::parser::parse_expression(&ctx, location, Lexer::new(&ctx, location.file, &mut bytes))?;
     if bytes.next().is_some() {
         return Err(DMError::new(location, format!("leftover: {:?} {}", from_utf8_or_latin1_borrowed(&input), bytes.len())));
     }
diff --git a/src/dreammaker/parser.rs b/src/dreammaker/parser.rs
index c03b9e13..34c91aea 100644
--- a/src/dreammaker/parser.rs
+++ b/src/dreammaker/parser.rs
@@ -26,6 +26,19 @@ where
     Parser::new(context, iter.into_iter()).parse_object_tree()
 }
 
+/// Parse a token stream into an expression.
+///
+/// Fatal errors will be directly returned and miscellaneous diagnostics will
+/// be registered with the provided `Context`.
+pub fn parse_expression<I>(context: &Context, location: Location, iter: I) -> Result<Expression, DMError>
+where
+    I: IntoIterator<Item=LocatedToken>,
+{
+    let mut parser = Parser::new(context, iter.into_iter());
+    parser.set_fallback_location(location);
+    parser.require_expression()
+}
+
 type Ident = String;
 
 // ----------------------------------------------------------------------------
@@ -399,7 +412,7 @@ where
         self.procs = true;
     }
 
-    pub fn set_fallback_location(&mut self, fallback: Location) {
+    fn set_fallback_location(&mut self, fallback: Location) {
         assert!(self.location == Default::default());
         self.location = fallback;
     }
@@ -1571,7 +1584,7 @@ where
     }
 
     /// Parse an expression at the current position.
-    pub fn require_expression(&mut self) -> Result<Expression, DMError> {
+    fn require_expression(&mut self) -> Result<Expression, DMError> {
         Ok(require!(self.expression()))
     }
 
diff --git a/src/dreammaker/preprocessor.rs b/src/dreammaker/preprocessor.rs
index 8f12c1cf..6117b774 100644
--- a/src/dreammaker/preprocessor.rs
+++ b/src/dreammaker/preprocessor.rs
@@ -554,12 +554,11 @@ impl<'ctx> Preprocessor<'ctx> {
             return Ok(false);
         }
 
-        let mut parser = ::parser::Parser::new(
+        let expr = crate::parser::parse_expression(
             self.context,
-            self.output.drain(..).map(|token| LocatedToken::new(start, token)),
-        );
-        parser.set_fallback_location(start);
-        let expr = parser.require_expression()?;
+            start,
+            self.output.drain(..).map(|token| LocatedToken::new(start, token))
+        )?;
         Ok(::constants::preprocessor_evaluate(start, expr, &self.defines)?.to_bool())
     }