better help text for "match -> if let" lint

Implements the suggestion from #87.

Changes span_help_and_lint(), which is only used for this lint,
to use fileline_help() instead of span_help() to avoid printing
the span twice.

Also adds complete suggested new code. I had to distinguish
between blocks, which need no additionals braces, and other exprs.
This commit is contained in:
Georg Brandl 2015-08-11 19:26:33 +02:00
parent 50ebdaa79d
commit cab9905705
3 changed files with 18 additions and 9 deletions

View file

@ -43,13 +43,20 @@ impl LintPass for MiscPass {
// an enum is extended. So we only consider cases where a `_` wildcard is used
if arms[1].pats[0].node == PatWild(PatWildSingle) &&
arms[0].pats.len() == 1 {
let body_code = snippet(cx, arms[0].body.span, "..");
let suggestion = if let ExprBlock(_) = arms[0].body.node {
body_code.into_owned()
} else {
format!("{{ {} }}", body_code)
};
span_help_and_lint(cx, SINGLE_MATCH, expr.span,
"You seem to be trying to use match for \
destructuring a single type. Did you mean to \
destructuring a single pattern. Did you mean to \
use `if let`?",
&*format!("Try if let {} = {} {{ ... }}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."))
&*format!("Try\nif let {} = {} {}",
snippet(cx, arms[0].pats[0].span, ".."),
snippet(cx, ex.span, ".."),
suggestion)
);
}
}

View file

@ -77,10 +77,10 @@ pub fn span_lint(cx: &Context, lint: &'static Lint, sp: Span, msg: &str) {
cx.span_lint(lint, sp, msg);
}
pub fn span_help_and_lint(cx: &Context, lint: &'static Lint, span: Span,
pub fn span_help_and_lint(cx: &Context, lint: &'static Lint, span: Span,
msg: &str, help: &str) {
span_lint(cx, lint, span, msg);
if cx.current_level(lint) != Level::Allow {
cx.sess().span_help(span, help);
cx.sess().fileline_help(span, help);
}
}

8
tests/compile-fail/match_if_let.rs Normal file → Executable file
View file

@ -6,8 +6,10 @@
fn main(){
let x = Some(1u8);
match x { //~ ERROR You seem to be trying to use match
//~^ HELP Try if let Some(y) = x { ... }
Some(y) => println!("{:?}", y),
//~^ HELP Try
Some(y) => {
println!("{:?}", y);
}
_ => ()
}
// Not linted
@ -17,7 +19,7 @@ fn main(){
}
let z = (1u8,1u8);
match z { //~ ERROR You seem to be trying to use match
//~^ HELP Try if let (2...3, 7...9) = z { ... }
//~^ HELP Try
(2...3, 7...9) => println!("{:?}", z),
_ => {}
}