Better tracking for beginning and ending positions of mappings. (#10)

Previously, we often used the scanner state to infer the positions of
mappings. This is sometimes wrong, because the scanner has already
scanned ahead by the time the mapping is parsed.

This commit adds a check to the test suite, asserting that parser event
positions are all observed in order, and it fixes the scanner and parser
to make the new check pass.

parser/src/parser.rs

@@ -7,6 +7,7 @@
 use crate::{
     input::{str::StrInput, Input},
     scanner::{ScanError, Scanner, Span, TScalarStyle, Token, TokenType},
+    Marker,
 };
 
 use std::collections::HashMap;
@@ -29,7 +30,7 @@ enum State {
     FlowSequenceEntry,
     FlowSequenceEntryMappingKey,
     FlowSequenceEntryMappingValue,
-    FlowSequenceEntryMappingEnd,
+    FlowSequenceEntryMappingEnd(Marker),
     FlowMappingFirstKey,
     FlowMappingKey,
     FlowMappingValue,
@@ -559,7 +560,7 @@ impl<T: Input> Parser<T> {
 
             State::FlowSequenceEntryMappingKey => self.flow_sequence_entry_mapping_key(),
             State::FlowSequenceEntryMappingValue => self.flow_sequence_entry_mapping_value(),
-            State::FlowSequenceEntryMappingEnd => self.flow_sequence_entry_mapping_end(),
+            State::FlowSequenceEntryMappingEnd(mark) => self.flow_sequence_entry_mapping_end(mark),
             State::FlowMappingEmptyValue => self.flow_mapping_value(true),
 
             /* impossible */
@@ -1070,27 +1071,26 @@ impl<T: Input> Parser<T> {
             Token(_, TokenType::Value) => {
                 self.skip();
                 self.state = State::FlowSequenceEntryMappingValue;
-                if let Token(mark, TokenType::FlowEntry | TokenType::FlowSequenceEnd) =
+                let Token(span, ref tok) = *self.peek_token()?;
-                    *self.peek_token()?
+                if matches!(tok, TokenType::FlowEntry | TokenType::FlowSequenceEnd) {
-                {
+                    self.state = State::FlowSequenceEntryMappingEnd(span.end);
-                    self.state = State::FlowSequenceEntryMappingEnd;
+                    Ok((Event::empty_scalar(), span))
-                    Ok((Event::empty_scalar(), mark))
                 } else {
-                    self.push_state(State::FlowSequenceEntryMappingEnd);
+                    self.push_state(State::FlowSequenceEntryMappingEnd(span.end));
                     self.parse_node(false, false)
                 }
             }
             Token(mark, _) => {
-                self.state = State::FlowSequenceEntryMappingEnd;
+                self.state = State::FlowSequenceEntryMappingEnd(mark.end);
                 Ok((Event::empty_scalar(), mark))
             }
         }
     }
 
     #[allow(clippy::unnecessary_wraps)]
-    fn flow_sequence_entry_mapping_end(&mut self) -> ParseResult {
+    fn flow_sequence_entry_mapping_end(&mut self, mark: Marker) -> ParseResult {
         self.state = State::FlowSequenceEntry;
-        Ok((Event::MappingEnd, Span::empty(self.scanner.mark())))
+        Ok((Event::MappingEnd, Span::empty(mark)))
     }
 
     /// Resolve a tag from the handle and the suffix.

parser/src/scanner.rs

@@ -2403,7 +2403,7 @@ impl<T: Input> Scanner<T> {
                 }
                 self.insert_token(
                     sk.token_number - self.tokens_parsed,
-                    Token(Span::empty(self.mark), TokenType::FlowMappingStart),
+                    Token(Span::empty(sk.mark), TokenType::FlowMappingStart),
                 );
             }
 
@@ -2412,7 +2412,7 @@ impl<T: Input> Scanner<T> {
                 sk.mark.col,
                 Some(sk.token_number),
                 TokenType::BlockMappingStart,
-                start_mark,
+                sk.mark,
             );
             self.roll_one_col_indent();
 
@@ -2421,7 +2421,7 @@ impl<T: Input> Scanner<T> {
         } else {
             if is_implicit_flow_mapping {
                 self.tokens
-                    .push_back(Token(Span::empty(self.mark), TokenType::FlowMappingStart));
+                    .push_back(Token(Span::empty(start_mark), TokenType::FlowMappingStart));
             }
             // The ':' indicator follows a complex key.
             if self.flow_level == 0 {

parser/tests/yaml-test-suite.rs

@@ -3,7 +3,9 @@ use std::fs::{self, DirEntry};
 use libtest_mimic::{run_tests, Arguments, Outcome, Test};
 
 use saphyr::{Hash, Yaml};
-use saphyr_parser::{Event, EventReceiver, Parser, ScanError, TScalarStyle, Tag};
+use saphyr_parser::{
+    Event, Marker, Parser, ScanError, Span, SpannedEventReceiver, TScalarStyle, Tag,
+};
 
 type Result<T, E = Box<dyn std::error::Error>> = std::result::Result<T, E>;
 
@@ -34,28 +36,49 @@ fn main() -> Result<()> {
 
 fn run_yaml_test(test: &Test<YamlTest>) -> Outcome {
     let desc = &test.data;
-    let actual_events = parse_to_events(&desc.yaml);
+    let reporter = parse_to_events(&desc.yaml);
-    let events_diff = actual_events.map(|events| events_differ(&events, &desc.expected_events));
+    let actual_events = reporter.as_ref().map(|reporter| &reporter.events);
-    let mut error_text = match (&events_diff, desc.expected_error) {
+    let events_diff = actual_events.map(|events| events_differ(events, &desc.expected_events));
+    let error_text = match (&events_diff, desc.expected_error) {
         (Ok(x), true) => Some(format!("no error when expected: {x:#?}")),
         (Err(_), true) | (Ok(None), false) => None,
         (Err(e), false) => Some(format!("unexpected error {e:?}")),
         (Ok(Some(diff)), false) => Some(format!("events differ: {diff}")),
     };
 
-    // Show a caret on error.
+    if let Some(mut txt) = error_text {
-    if let Some(text) = &mut error_text {
+        add_error_context(
+            &mut txt,
+            desc,
+            events_diff.err().map(saphyr::ScanError::marker),
+        );
+        Outcome::Failed { msg: Some(txt) }
+    } else if let Some((mut msg, span)) = reporter
+        .as_ref()
+        .ok()
+        .and_then(|reporter| reporter.span_failures.first().cloned())
+    {
+        add_error_context(&mut msg, desc, Some(&span.start));
+        Outcome::Failed { msg: Some(msg) }
+    } else {
+        Outcome::Passed
+    }
+}
+
+// Enrich the error message with the failing input, and a caret pointing
+// at the position that errored.
+fn add_error_context(text: &mut String, desc: &YamlTest, marker: Option<&Marker>) {
     use std::fmt::Write;
     let _ = writeln!(text, "\n### Input:\n{}\n### End", desc.yaml_visual);
-        if let Err(err) = &events_diff {
+    if let Some(mark) = marker {
         writeln!(text, "### Error position").unwrap();
         let mut lines = desc.yaml.lines();
-            for _ in 0..(err.marker().line() - 1) {
+        for _ in 0..(mark.line() - 1) {
             let l = lines.next().unwrap();
             writeln!(text, "{l}").unwrap();
         }
         writeln!(text, "\x1B[91;1m{}", lines.next().unwrap()).unwrap();
-            for _ in 0..err.marker().col() {
+        for _ in 0..mark.col() {
             write!(text, " ").unwrap();
         }
         writeln!(text, "^\x1b[m").unwrap();
@@ -66,12 +89,6 @@ fn run_yaml_test(test: &Test<YamlTest>) -> Outcome {
     }
 }
 
-    match error_text {
-        None => Outcome::Passed,
-        Some(txt) => Outcome::Failed { msg: Some(txt) },
-    }
-}
-
 fn load_tests_from_file(entry: &DirEntry) -> Result<Vec<Test<YamlTest>>> {
     let file_name = entry.file_name().to_string_lossy().to_string();
     let test_name = file_name
@@ -118,26 +135,37 @@ fn load_tests_from_file(entry: &DirEntry) -> Result<Vec<Test<YamlTest>>> {
     Ok(result)
 }
 
-fn parse_to_events(source: &str) -> Result<Vec<String>, ScanError> {
+fn parse_to_events(source: &str) -> Result<EventReporter, ScanError> {
-    let mut reporter = EventReporter::new();
+    let mut reporter = EventReporter::default();
     for x in Parser::new_from_str(source) {
-        reporter.on_event(x?.0);
+        let x = x?;
+        reporter.on_event(x.0, x.1);
     }
-    Ok(reporter.events)
+    Ok(reporter)
 }
 
-struct EventReporter {
+#[derive(Default)]
-    events: Vec<String>,
+/// A [`SpannedEventReceiver`] checking for inconsistencies in event [`Spans`].
+pub struct EventReporter {
+    pub events: Vec<String>,
+    last_span: Option<(Event, Span)>,
+    pub span_failures: Vec<(String, Span)>,
 }
 
-impl EventReporter {
+impl SpannedEventReceiver for EventReporter {
-    fn new() -> Self {
+    fn on_event(&mut self, ev: Event, span: Span) {
-        Self { events: vec![] }
+        if let Some((last_ev, last_span)) = self.last_span.take() {
+            if span.start.index() < last_span.start.index()
+                || span.end.index() < last_span.end.index()
+            {
+                self.span_failures.push((
+                    format!("event {ev:?}@{span:?} came before event {last_ev:?}@{last_span:?}"),
+                    span,
+                ));
             }
         }
+        self.last_span = Some((ev.clone(), span));
 
-impl EventReceiver for EventReporter {
-    fn on_event(&mut self, ev: Event) {
         let line: String = match ev {
             Event::StreamStart => "+STR".into(),
             Event::StreamEnd => "-STR".into(),