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Make case expressions fault tolerant #4169

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Jan 16, 2025
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Make case expressions fault tolerant #4169

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c9bfe21
Make case expressions fault tolerant
GearsDatapacks Jan 12, 2025
d962f3f
Changelog
GearsDatapacks Jan 12, 2025
b9976fb
Clippy
GearsDatapacks Jan 12, 2025
6df87b4
Tests
GearsDatapacks Jan 12, 2025
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5 changes: 5 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -17,6 +17,11 @@
shell starting from OTP27.
([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Parsing of `case` expressions is now fault tolerant. If a `case` expressions
is missing its body, the compiler can still perform type inference. This also
allows the Language Server to provide completion hints for `case` subjects.
([Surya Rose](https://github.com/GearsDatapacks))

### Build tool

- `gleam new` now has refined project name validation - rather than failing on
Expand Down
3 changes: 2 additions & 1 deletion compiler-core/src/ast/untyped.rs
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Expand Up @@ -69,7 +69,8 @@ pub enum UntypedExpr {
Case {
location: SrcSpan,
subjects: Vec<Self>,
clauses: Vec<Clause<Self, (), ()>>,
// None if the case expression is missing a body.
clauses: Option<Vec<Clause<Self, (), ()>>>,
},

FieldAccess {
Expand Down
38 changes: 20 additions & 18 deletions compiler-core/src/ast_folder.rs
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Expand Up @@ -457,23 +457,25 @@ pub trait UntypedExprFolder: TypeAstFolder + UntypedConstantFolder + PatternFold
clauses,
} => {
let subjects = subjects.into_iter().map(|e| self.fold_expr(e)).collect();
let clauses = clauses
.into_iter()
.map(|mut c| {
c.pattern = c
.pattern
.into_iter()
.map(|p| self.fold_pattern(p))
.collect();
c.alternative_patterns = c
.alternative_patterns
.into_iter()
.map(|p| p.into_iter().map(|p| self.fold_pattern(p)).collect())
.collect();
c.then = self.fold_expr(c.then);
c
})
.collect();
let clauses = clauses.map(|clauses| {
clauses
.into_iter()
.map(|mut c| {
c.pattern = c
.pattern
.into_iter()
.map(|p| self.fold_pattern(p))
.collect();
c.alternative_patterns = c
.alternative_patterns
.into_iter()
.map(|p| p.into_iter().map(|p| self.fold_pattern(p)).collect())
.collect();
c.then = self.fold_expr(c.then);
c
})
.collect()
});
UntypedExpr::Case {
location,
subjects,
Expand Down Expand Up @@ -742,7 +744,7 @@ pub trait UntypedExprFolder: TypeAstFolder + UntypedConstantFolder + PatternFold
&mut self,
location: SrcSpan,
subjects: Vec<UntypedExpr>,
clauses: Vec<UntypedClause>,
clauses: Option<Vec<UntypedClause>>,
) -> UntypedExpr {
UntypedExpr::Case {
location,
Expand Down
2 changes: 1 addition & 1 deletion compiler-core/src/call_graph.rs
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Expand Up @@ -278,7 +278,7 @@ impl<'a> CallGraphBuilder<'a> {
for subject in subjects {
self.expression(subject);
}
for clause in clauses {
for clause in clauses.as_deref().unwrap_or_default() {
let names = self.names.clone();
for pattern in &clause.pattern {
self.pattern(pattern);
Expand Down
21 changes: 21 additions & 0 deletions compiler-core/src/error.rs
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Expand Up @@ -3066,6 +3066,27 @@ The missing patterns are:\n"
}
}

TypeError::MissingCaseBody { location } => {
let text = wrap(
"This case expression is missing its body."
);
Diagnostic {
title: "Missing case body".into(),
text,
hint: None,
level: Level::Error,
location: Some(Location {
src: src.clone(),
path: path.to_path_buf(),
label: Label {
text: None,
span: *location,
},
extra_labels: Vec::new(),
}),
}
}

TypeError::UnsupportedExpressionTarget {
location,
target: current_target,
Expand Down
2 changes: 1 addition & 1 deletion compiler-core/src/format.rs
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Expand Up @@ -1030,7 +1030,7 @@ impl<'comments> Formatter<'comments> {
subjects,
clauses,
location,
} => self.case(subjects, clauses, location),
} => self.case(subjects, clauses.as_deref().unwrap_or_default(), location),

UntypedExpr::FieldAccess {
label, container, ..
Expand Down
15 changes: 15 additions & 0 deletions compiler-core/src/language_server/tests/completion.rs
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Expand Up @@ -1886,3 +1886,18 @@ pub fn map(_, _) { [] }
Position::new(3, 8)
);
}

#[test]
fn case_subject() {
let code = "
pub fn main(something: Bool) {
case so
}
";

assert_apply_completion!(
TestProject::for_source(code),
"something",
Position::new(2, 9)
);
}
14 changes: 14 additions & 0 deletions ..._server/tests/snapshots/gleam_core__language_server__tests__completion__case_subject.snap
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@@ -0,0 +1,14 @@
---
source: compiler-core/src/language_server/tests/completion.rs
expression: "\npub fn main(something: Bool) {\n case so\n}\n"
---
pub fn main(something: Bool) {
case so|
}


----- After applying completion -----

pub fn main(something: Bool) {
case something
}
35 changes: 24 additions & 11 deletions compiler-core/src/parse.rs
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Expand Up @@ -701,20 +701,33 @@ where
self.advance();
let subjects =
Parser::series_of(self, &Parser::parse_expression, Some(&Token::Comma))?;
let _ = self.expect_one_following_series(&Token::LeftBrace, "an expression")?;
let clauses = Parser::series_of(self, &Parser::parse_case_clause, None)?;
let (_, end) =
self.expect_one_following_series(&Token::RightBrace, "a case clause")?;
if subjects.is_empty() {
return parse_error(
ParseErrorType::ExpectedExpr,
SrcSpan { start, end: case_e },
);
if self.maybe_one(&Token::LeftBrace).is_some() {
let clauses = Parser::series_of(self, &Parser::parse_case_clause, None)?;
let (_, end) =
self.expect_one_following_series(&Token::RightBrace, "a case clause")?;
if subjects.is_empty() {
return parse_error(
ParseErrorType::ExpectedExpr,
SrcSpan { start, end: case_e },
);
} else {
UntypedExpr::Case {
location: SrcSpan { start, end },
subjects,
clauses: Some(clauses),
}
}
} else {
UntypedExpr::Case {
location: SrcSpan { start, end },
location: SrcSpan::new(
start,
subjects
.last()
.map(|subject| subject.location().end)
.unwrap_or(case_e),
),
subjects,
clauses,
clauses: None,
}
}
}
Expand Down
134 changes: 68 additions & 66 deletions compiler-core/src/parse/snapshots/gleam_core__parse__tests__arithmetic_in_guards.snap
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Expand Up @@ -27,86 +27,88 @@ expression: "\ncase 2, 3 {\n x, y if x + y == 1 -> True\n}"
int_value: 3,
},
],
clauses: [
Clause {
location: SrcSpan {
start: 17,
end: 43,
},
pattern: [
Variable {
location: SrcSpan {
start: 17,
end: 18,
},
name: "x",
type_: (),
origin: Variable(
"x",
),
clauses: Some(
[
Clause {
location: SrcSpan {
start: 17,
end: 43,
},
Variable {
location: SrcSpan {
start: 20,
end: 21,
pattern: [
Variable {
location: SrcSpan {
start: 17,
end: 18,
},
name: "x",
type_: (),
origin: Variable(
"x",
),
},
name: "y",
type_: (),
origin: Variable(
"y",
),
},
],
alternative_patterns: [],
guard: Some(
Equals {
location: SrcSpan {
start: 25,
end: 35,
Variable {
location: SrcSpan {
start: 20,
end: 21,
},
name: "y",
type_: (),
origin: Variable(
"y",
),
},
left: AddInt {
],
alternative_patterns: [],
guard: Some(
Equals {
location: SrcSpan {
start: 25,
end: 30,
end: 35,
},
left: Var {
left: AddInt {
location: SrcSpan {
start: 25,
end: 26,
},
type_: (),
name: "x",
},
right: Var {
location: SrcSpan {
start: 29,
end: 30,
},
type_: (),
name: "y",
},
},
right: Constant(
Int {
location: SrcSpan {
start: 34,
end: 35,
left: Var {
location: SrcSpan {
start: 25,
end: 26,
},
type_: (),
name: "x",
},
right: Var {
location: SrcSpan {
start: 29,
end: 30,
},
type_: (),
name: "y",
},
value: "1",
int_value: 1,
},
),
},
),
then: Var {
location: SrcSpan {
start: 39,
end: 43,
right: Constant(
Int {
location: SrcSpan {
start: 34,
end: 35,
},
value: "1",
int_value: 1,
},
),
},
),
then: Var {
location: SrcSpan {
start: 39,
end: 43,
},
name: "True",
},
name: "True",
},
},
],
],
),
},
),
]
24 changes: 24 additions & 0 deletions ...iler-core/src/parse/snapshots/gleam_core__parse__tests__case_expression_without_body.snap
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@@ -0,0 +1,24 @@
---
source: compiler-core/src/parse/tests.rs
expression: case a
---
[
Expression(
Case {
location: SrcSpan {
start: 0,
end: 6,
},
subjects: [
Var {
location: SrcSpan {
start: 5,
end: 6,
},
name: "a",
},
],
clauses: None,
},
),
]
3 changes: 1 addition & 2 deletions compiler-core/src/parse/snapshots/gleam_core__parse__tests__case_invalid_expression.snap
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Expand Up @@ -19,5 +19,4 @@ error: Syntax error
│ ^^^^ I was not expecting this

Found the keyword `type`, expected one of:
- `{`
- an expression
- `}`
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