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Merged
konojunya merged 3 commits into from
Sep 3, 2026
Merged

Add actionable compiler diagnostics #8

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849a4bb
Add structured diagnostic expectations
konojunya Sep 3, 2026
0f0e6c0
Report parser expectations
konojunya Sep 3, 2026
cdd0969
Add actionable compiler guidance
konojunya Sep 3, 2026
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41 changes: 41 additions & 0 deletions src/diagnostic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -94,6 +94,8 @@ pub struct Diagnostic {
pub message: String,
/// Primary source span.
pub span: Span,
/// Ordered source values or constructs valid at the primary span.
pub expected: Vec<String>,
/// Optional corrective guidance.
pub help: Option<String>,
/// Other declarations or references involved in the problem.
Expand All @@ -107,6 +109,7 @@ impl Diagnostic {
severity: Severity::Error,
message: message.into(),
span,
expected: Vec::new(),
help: None,
related: Vec::new(),
}
Expand All @@ -118,6 +121,7 @@ impl Diagnostic {
severity: Severity::Warning,
message: message.into(),
span,
expected: Vec::new(),
help: None,
related: Vec::new(),
}
Expand All @@ -128,6 +132,15 @@ impl Diagnostic {
self
}

pub(crate) fn with_expected<I, S>(mut self, expected: I) -> Self
where
I: IntoIterator<Item = S>,
S: Into<String>,
{
self.expected = expected.into_iter().map(Into::into).collect();
self
}

pub(crate) fn with_related(mut self, message: impl Into<String>, span: Span) -> Self {
self.related.push(RelatedInformation {
message: message.into(),
Expand All @@ -136,3 +149,31 @@ impl Diagnostic {
self
}
}

#[cfg(test)]
mod tests {
use super::{Diagnostic, SourcePosition, Span};

#[test]
fn diagnostics_default_to_no_expected_values() {
let diagnostic = Diagnostic::error(
"STK2002",
"Unexpected value.",
Span::point(SourcePosition::start()),
);

assert!(diagnostic.expected.is_empty());
}

#[test]
fn diagnostics_preserve_expected_value_order() {
let diagnostic = Diagnostic::error(
"STK2002",
"Unknown direction.",
Span::point(SourcePosition::start()),
)
.with_expected(["right", "down"]);

assert_eq!(diagnostic.expected, ["right", "down"]);
}
}
157 changes: 101 additions & 56 deletions src/lexer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,11 +32,14 @@ pub(crate) fn tokenize(source: &str) -> LexResult<Vec<Token>> {
line: 1,
column: 2,
};
return Err(Box::new(Diagnostic::error(
"STK1002",
"A byte order mark is not permitted.",
Span { start, end },
)));
return Err(Box::new(
Diagnostic::error(
"STK1002",
"A byte order mark is not permitted.",
Span { start, end },
)
.with_help("Remove the UTF-8 byte order mark at the start of the file."),
));
}

Lexer::new(source).tokenize()
Expand Down Expand Up @@ -131,14 +134,18 @@ impl<'source> Lexer<'source> {

loop {
let Some(character) = self.peek() else {
return Err(Box::new(Diagnostic::error(
"STK2003",
"Input ended before the string was closed.",
Span {
start,
end: self.position,
},
)));
return Err(Box::new(
Diagnostic::error(
"STK2003",
"Input ended before the string was closed.",
Span {
start,
end: self.position,
},
)
.with_expected(["\""])
.with_help("Add a closing double quote."),
));
};

match character {
Expand All @@ -162,22 +169,30 @@ impl<'source> Lexer<'source> {
start: self.position,
end: self.position_after_current(),
};
return Err(Box::new(Diagnostic::error(
"STK1003",
"Strings cannot contain line breaks or tabs.",
span,
)));
return Err(Box::new(
Diagnostic::error(
"STK1003",
"Strings cannot contain line breaks or tabs.",
span,
)
.with_help(
"Remove the line break or tab; Stack strings must stay on one line.",
),
));
}
value_character if value_character.is_control() => {
let span = Span {
start: self.position,
end: self.position_after_current(),
};
return Err(Box::new(Diagnostic::error(
"STK1003",
"Strings cannot contain control characters.",
span,
)));
return Err(Box::new(
Diagnostic::error(
"STK1003",
"Strings cannot contain control characters.",
span,
)
.with_help("Remove the control character from the string."),
));
}
value_character => {
value.push(value_character);
Expand Down Expand Up @@ -257,14 +272,18 @@ impl<'source> Lexer<'source> {
fn lex_escape(&mut self, value: &mut String, string_start: SourcePosition) -> LexResult<()> {
let escape_start = self.position;
let Some(character) = self.peek() else {
return Err(Box::new(Diagnostic::error(
"STK1003",
"Input ended inside a string escape.",
Span {
start: string_start,
end: self.position,
},
)));
return Err(Box::new(
Diagnostic::error(
"STK1003",
"Input ended inside a string escape.",
Span {
start: string_start,
end: self.position,
},
)
.with_expected([r#"\""#, r#"\\"#, r#"\uXXXX"#])
.with_help("Complete the escape using a supported Stack string escape."),
));
};

match character {
Expand Down Expand Up @@ -303,14 +322,19 @@ impl<'source> Lexer<'source> {
return Err(self.invalid_escape(escape_start));
};
if decoded.is_control() || matches!(decoded, '\n' | '\r' | '\t') {
return Err(Box::new(Diagnostic::error(
"STK1003",
"A string escape decoded to a prohibited control value.",
Span {
start: escape_start,
end: self.position,
},
)));
return Err(Box::new(
Diagnostic::error(
"STK1003",
"A string escape decoded to a prohibited control value.",
Span {
start: escape_start,
end: self.position,
},
)
.with_help(
"Use a printable Unicode scalar that is not a line break or tab.",
),
));
}
value.push(decoded);
}
Expand All @@ -337,25 +361,32 @@ impl<'source> Lexer<'source> {
}

fn invalid_escape(&self, start: SourcePosition) -> Box<Diagnostic> {
Box::new(Diagnostic::error(
"STK1003",
"The string contains an invalid escape.",
Span {
start,
end: self.position,
},
))
Box::new(
Diagnostic::error(
"STK1003",
"The string contains an invalid escape.",
Span {
start,
end: self.position,
},
)
.with_expected([r#"\""#, r#"\\"#, r#"\uXXXX"#])
.with_help("Use an escaped double quote, backslash, or Unicode code unit."),
)
}

fn invalid_surrogate(&self, start: SourcePosition) -> Box<Diagnostic> {
Box::new(Diagnostic::error(
"STK1003",
"The string contains an unpaired Unicode surrogate.",
Span {
start,
end: self.position,
},
))
Box::new(
Diagnostic::error(
"STK1003",
"The string contains an unpaired Unicode surrogate.",
Span {
start,
end: self.position,
},
)
.with_help("Pair high and low surrogates or use a non-surrogate Unicode code unit."),
)
}

fn lex_bare(&mut self) -> TokenKind {
Expand Down Expand Up @@ -512,12 +543,26 @@ mod tests {
let result = tokenize(source);
assert!(matches!(result, Err(diagnostic) if diagnostic.code == "STK1003"));
}

let invalid_escape = tokenize(r#""\n""#);
assert!(matches!(
invalid_escape,
Err(diagnostic)
if diagnostic.expected == [r#"\""#, r#"\\"#, r#"\uXXXX"#]
&& diagnostic.help.is_some()
));
}

#[test]
fn reports_an_unterminated_string() {
let result = tokenize("\"unfinished");
assert!(matches!(result, Err(diagnostic) if diagnostic.code == "STK2003"));
assert!(matches!(
result,
Err(diagnostic)
if diagnostic.code == "STK2003"
&& diagnostic.expected == ["\""]
&& diagnostic.help.as_deref() == Some("Add a closing double quote.")
));
}

#[test]
Expand Down
1 change: 1 addition & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,7 @@ fn invalid_utf8_diagnostic(source: &[u8], error: std::str::Utf8Error) -> Diagnos
"Input is not valid UTF-8.",
diagnostic::Span::point(position),
)
.with_help("Save the source as UTF-8 and replace the invalid byte sequence.")
}

#[cfg(test)]
Expand Down
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