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bugfix(semantic): writeln!(f) with no format string writes a newline.
`writeln!(f)` (a formatter with no format string) errored with "Macro expected format string argument", though in Rust it writes just a newline. Accept the no-format-string case for `writeln!` and emit a newline; `write!(f)` still requires a format string. This also makes `println!()` valid — it expands to `writeln!(f, )` — matching its documented "prints an empty line" example, while `print!()` → `write!(f, )` still errors.
1 parent 808c713 commit 58e8554

4 files changed

Lines changed: 35 additions & 15 deletions

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‎crates/cairo-lang-semantic/src/expr/test_data/inline_macros‎

Lines changed: 0 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -575,11 +575,6 @@ error[E2200]: Plugin diagnostic: Macro expected formatter argument.
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writeln!();
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^
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error[E2200]: Plugin diagnostic: Macro expected format string argument.
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--> lib.cairo:12:13
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writeln!(f);
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^
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error[E2200]: Plugin diagnostic: Formatter argument must not be a string literal.
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--> lib.cairo:15:14
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writeln!("{}", ba);
@@ -943,11 +938,6 @@ error[E2200]: Plugin diagnostic: Macro `writeln` does not support this bracket t
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println!["{}", ba];
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^
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946-
error[E2200]: Plugin diagnostic: Macro expected format string argument.
947-
--> lib.cairo:8:13
948-
println!();
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^
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error[E2200]: Plugin diagnostic: Format string argument must be a string literal.
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--> lib.cairo:11:14
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println!(ba);

‎crates/cairo-lang-semantic/src/inline_macros/write.rs‎

Lines changed: 19 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -113,7 +113,7 @@ fn generate_code_inner<'db>(
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db: &'db dyn Database,
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with_newline: bool,
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) -> InlinePluginResult<'db> {
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let info = match FormattingInfo::extract(db, syntax) {
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let info = match FormattingInfo::extract(db, syntax, with_newline) {
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Ok(info) => info,
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Err(diagnostics) => return InlinePluginResult { code: None, diagnostics },
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};
@@ -163,6 +163,7 @@ impl<'db> FormattingInfo<'db> {
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fn extract(
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db: &'db dyn Database,
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syntax: &ast::ExprInlineMacro<'db>,
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with_newline: bool,
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) -> Result<FormattingInfo<'db>, Vec<PluginDiagnostic<'db>>> {
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let Some(legacy_inline_macro) = syntax.as_legacy_inline_macro(db) else {
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return Err(vec![not_legacy_macro_diagnostic(syntax.as_syntax_node().stable_ptr(db))]);
@@ -206,10 +207,23 @@ impl<'db> FormattingInfo<'db> {
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)]);
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}
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let Some(format_string_arg) = args_iter.next() else {
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return Err(vec![error_with_inner_span(
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arguments.lparen(db).as_syntax_node(),
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"Macro expected format string argument.",
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)]);
210+
// `writeln!(f)` (no format string) writes just a newline; `write!(f)` still errors.
211+
// There is no format string, so the arg node is unused here — reuse the formatter's.
212+
return if with_newline {
213+
Ok(FormattingInfo {
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formatter_arg_node: RewriteNode::from_ast_trimmed(&formatter_arg),
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format_string_arg: formatter_arg.clone(),
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format_string: String::new(),
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format_string_source: "",
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args: vec![],
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macro_ast: syntax.clone(),
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})
221+
} else {
222+
Err(vec![error_with_inner_span(
223+
arguments.lparen(db).as_syntax_node(),
224+
"Macro expected format string argument.",
225+
)])
226+
};
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};
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let Some(format_string_expr) = try_extract_unnamed_arg(db, &format_string_arg) else {
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return Err(vec![error_with_inner_span(

‎tests/bug_samples/lib.cairo‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,7 @@ mod ecdsa_completeness;
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mod generic_cycles;
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mod inconsistent_gas;
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mod indirect_impl_alias;
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mod writeln_no_format_string;
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mod issue2114;
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mod issue2147;
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mod issue2152;

‎tests/bug_samples/writeln_no_format_string.cairo‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
1+
//! Regression: `writeln!(f)` (a formatter with no format string) writes just a newline, matching
2+
//! Rust. It previously errored with "Macro expected format string argument". `println!()` is valid
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//! for free via the same `writeln!(f, )` expansion; `write!(f)` / `print!()` still require a format
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//! string.
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6+
use core::fmt::Formatter;
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8+
#[test]
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fn test_writeln_with_no_format_string_writes_newline() {
10+
let mut f: Formatter = Default::default();
11+
let _ = writeln!(f);
12+
assert!(f.buffer == "\n");
13+
// `println!()` (no arguments) now compiles too, via the same expansion.
14+
println!();
15+
}

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