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auto merge of #11718 : ktt3ja/rust/borrowck-error-msg, r=brson

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A mutable and immutable borrow place some restrictions on what you can
with the variable until the borrow ends. This commit attempts to convey
to the user what those restrictions are. Also, if the original borrow is
a mutable borrow, the error message has been changed (more specifically,
i. "cannot borrow `x` as immutable because it is also borrowed as
mutable" and ii. "cannot borrow `x` as mutable more than once" have
been changed to "cannot borrow `x` because it is already borrowed as
mutable").

In addition, this adds a (custom) span note to communicate where the
original borrow ends.

```rust
fn main() {
    match true {
        true => {
            let mut x = 1;
            let y = &x;
            let z = &mut x;
        }
        false => ()
    }
}

test.rs:6:21: 6:27 error: cannot borrow `x` as mutable because it is already borrowed as immutable
test.rs:6             let z = &mut x;
                              ^~~~~~
test.rs:5:21: 5:23 note: previous borrow of `x` occurs here; the immutable borrow prevents subsequent moves or mutable borrows of `x` until the borrow ends
test.rs:5             let y = &x;
                              ^~
test.rs:7:10: 7:10 note: previous borrow ends here
test.rs:3         true => {
test.rs:4             let mut x = 1;
test.rs:5             let y = &x;
test.rs:6             let z = &mut x;
test.rs:7         }
                  ^
```

```rust
fn foo3(t0: &mut &mut int) {
    let t1 = &mut *t0;
    let p: &int = &**t0;
}

fn main() {}

test.rs:3:19: 3:24 error: cannot borrow `**t0` because it is already borrowed as mutable
test.rs:3     let p: &int = &**t0;
                            ^~~~~
test.rs:2:14: 2:22 note: previous borrow of `**t0` as mutable occurs here; the mutable borrow prevents subsequent moves, borrows, or modification of `**t0` until the borrow ends
test.rs:2     let t1 = &mut *t0;
                       ^~~~~~~~
test.rs:4:2: 4:2 note: previous borrow ends here
test.rs:1 fn foo3(t0: &mut &mut int) {
test.rs:2     let t1 = &mut *t0;
test.rs:3     let p: &int = &**t0;
test.rs:4 }
          ^
```

For the "previous borrow ends here" note, if the span is too long (has too many lines), then only the first and last lines are printed, and the middle is replaced with dot dot dot:
```rust
fn foo3(t0: &mut &mut int) {
    let t1 = &mut *t0;
    let p: &int = &**t0;



}

fn main() {}

test.rs:3:19: 3:24 error: cannot borrow `**t0` because it is already borrowed as mutable
test.rs:3     let p: &int = &**t0;
                            ^~~~~
test.rs:2:14: 2:22 note: previous borrow of `**t0` as mutable occurs here; the mutable borrow prevents subsequent moves, borrows, or modification of `**t0` until the borrow ends
test.rs:2     let t1 = &mut *t0;
                       ^~~~~~~~
test.rs:7:2: 7:2 note: previous borrow ends here
test.rs:1 fn foo3(t0: &mut &mut int) {
...
test.rs:7 }
          ^
```

(Sidenote: the `span_end_note` currently also has issue #11715)
This commit is contained in:
bors
2014-01-23 22:46:32 -08:00
parent bf9c25562d b3290d322e
commit cd8ee786f9
9 changed files with 144 additions and 33 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
src/libsyntax/codemap.rs
View File

@@ -308,10 +308,6 @@ impl CodeMap {
}
}
pub fn adjust_span(&self, sp: Span) -> Span {
sp
}
pub fn span_to_str(&self, sp: Span) -> ~str {
{
let files = self.files.borrow();

88
src/libsyntax/diagnostic.rs
View File

@@ -19,12 +19,16 @@ use extra::term;
static BUG_REPORT_URL: &'static str =
"http://static.rust-lang.org/doc/master/complement-bugreport.html";
// maximum number of lines we will print for each error; arbitrary.
static MAX_LINES: uint = 6u;
pub trait Emitter {
fn emit(&self,
cmsp: Option<(&codemap::CodeMap, Span)>,
msg: &str,
lvl: Level);
fn custom_emit(&self, cm: &codemap::CodeMap,
sp: Span, msg: &str, lvl: Level);
}
/// This structure is used to signify that a task has failed with a fatal error
@@ -55,6 +59,9 @@ impl SpanHandler {
pub fn span_note(@self, sp: Span, msg: &str) {
self.handler.emit(Some((&*self.cm, sp)), msg, Note);
}
pub fn span_end_note(@self, sp: Span, msg: &str) {
self.handler.custom_emit(&*self.cm, sp, msg, Note);
}
pub fn span_bug(@self, sp: Span, msg: &str) -> ! {
self.span_fatal(sp, ice_msg(msg));
}
@@ -122,6 +129,10 @@ impl Handler {
lvl: Level) {
self.emit.emit(cmsp, msg, lvl);
}
pub fn custom_emit(@self, cm: &codemap::CodeMap,
sp: Span, msg: &str, lvl: Level) {
self.emit.custom_emit(cm, sp, msg, lvl);
}
}
pub fn ice_msg(msg: &str) -> ~str {
@@ -239,17 +250,34 @@ impl Emitter for DefaultEmitter {
msg: &str,
lvl: Level) {
match cmsp {
Some((cm, sp)) => {
let sp = cm.adjust_span(sp);
let ss = cm.span_to_str(sp);
let lines = cm.span_to_lines(sp);
print_diagnostic(ss, lvl, msg);
highlight_lines(cm, sp, lvl, lines);
print_macro_backtrace(cm, sp);
}
Some((cm, sp)) => emit(cm, sp, msg, lvl, false),
None => print_diagnostic("", lvl, msg),
}
}
fn custom_emit(&self, cm: &codemap::CodeMap,
sp: Span, msg: &str, lvl: Level) {
emit(cm, sp, msg, lvl, true);
}
}
fn emit(cm: &codemap::CodeMap, sp: Span,
msg: &str, lvl: Level, custom: bool) {
let ss = cm.span_to_str(sp);
let lines = cm.span_to_lines(sp);
if custom {
// we want to tell compiletest/runtest to look at the last line of the
// span (since `custom_highlight_lines` displays an arrow to the end of
// the span)
let span_end = Span { lo: sp.hi, hi: sp.hi, expn_info: sp.expn_info};
let ses = cm.span_to_str(span_end);
print_diagnostic(ses, lvl, msg);
custom_highlight_lines(cm, sp, lvl, lines);
} else {
print_diagnostic(ss, lvl, msg);
highlight_lines(cm, sp, lvl, lines);
}
print_macro_backtrace(cm, sp);
}
fn highlight_lines(cm: &codemap::CodeMap,
@@ -260,12 +288,10 @@ fn highlight_lines(cm: &codemap::CodeMap,
let mut err = io::stderr();
let err = &mut err as &mut io::Writer;
// arbitrarily only print up to six lines of the error
let max_lines = 6u;
let mut elided = false;
let mut display_lines = lines.lines.as_slice();
if display_lines.len() > max_lines {
display_lines = display_lines.slice(0u, max_lines);
if display_lines.len() > MAX_LINES {
display_lines = display_lines.slice(0u, MAX_LINES);
elided = true;
}
// Print the offending lines
@@ -319,6 +345,44 @@ fn highlight_lines(cm: &codemap::CodeMap,
}
}
// Here are the differences between this and the normal `highlight_lines`:
// `custom_highlight_lines` will always put arrow on the last byte of the
// span (instead of the first byte). Also, when the span is too long (more
// than 6 lines), `custom_highlight_lines` will print the first line, then
// dot dot dot, then last line, whereas `highlight_lines` prints the first
// six lines.
fn custom_highlight_lines(cm: &codemap::CodeMap,
sp: Span,
lvl: Level,
lines: &codemap::FileLines) {
let fm = lines.file;
let mut err = io::stderr();
let err = &mut err as &mut io::Writer;
let lines = lines.lines.as_slice();
if lines.len() > MAX_LINES {
write!(err, "{}:{} {}\n", fm.name,
lines[0] + 1, fm.get_line(lines[0] as int));
write!(err, "...\n");
let last_line = lines[lines.len()-1];
write!(err, "{}:{} {}\n", fm.name,
last_line + 1, fm.get_line(last_line as int));
} else {
for line in lines.iter() {
write!(err, "{}:{} {}\n", fm.name,
*line + 1, fm.get_line(*line as int));
}
}
let last_line_start = format!("{}:{} ", fm.name, lines[lines.len()-1]+1);
let hi = cm.lookup_char_pos(sp.hi);
// Span seems to use half-opened interval, so subtract 1
let skip = last_line_start.len() + hi.col.to_uint() - 1;
let mut s = ~"";
skip.times(|| s.push_char(' '));
s.push_char('^');
print_maybe_styled(s + "\n", term::attr::ForegroundColor(lvl.color()));
}
fn print_macro_backtrace(cm: &codemap::CodeMap, sp: Span) {
for ei in sp.expn_info.iter() {
let ss = ei.callee.span.as_ref().map_or(~"", |span| cm.span_to_str(*span));