rustc_codegen_llvm/coverageinfo/mapgen/
spans.rs

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1use rustc_middle::mir::coverage::FunctionCoverageInfo;
2use rustc_span::source_map::SourceMap;
3use rustc_span::{BytePos, Pos, SourceFile, Span};
4use tracing::debug;
5
6use crate::coverageinfo::ffi;
7use crate::coverageinfo::mapgen::LocalFileId;
8
9/// Converts the span into its start line and column, and end line and column.
10///
11/// Line numbers and column numbers are 1-based. Unlike most column numbers emitted by
12/// the compiler, these column numbers are denoted in **bytes**, because that's what
13/// LLVM's `llvm-cov` tool expects to see in coverage maps.
14///
15/// Returns `None` if the conversion failed for some reason. This shouldn't happen,
16/// but it's hard to rule out entirely (especially in the presence of complex macros
17/// or other expansions), and if it does happen then skipping a span or function is
18/// better than an ICE or `llvm-cov` failure that the user might have no way to avoid.
19pub(crate) fn make_coverage_span(
20    file_id: LocalFileId,
21    source_map: &SourceMap,
22    fn_cov_info: &FunctionCoverageInfo,
23    file: &SourceFile,
24    span: Span,
25) -> Option<ffi::CoverageSpan> {
26    let span = ensure_non_empty_span(source_map, fn_cov_info, span)?;
27
28    let lo = span.lo();
29    let hi = span.hi();
30
31    // Column numbers need to be in bytes, so we can't use the more convenient
32    // `SourceMap` methods for looking up file coordinates.
33    let line_and_byte_column = |pos: BytePos| -> Option<(usize, usize)> {
34        let rpos = file.relative_position(pos);
35        let line_index = file.lookup_line(rpos)?;
36        let line_start = file.lines()[line_index];
37        // Line numbers and column numbers are 1-based, so add 1 to each.
38        Some((line_index + 1, (rpos - line_start).to_usize() + 1))
39    };
40
41    let (mut start_line, start_col) = line_and_byte_column(lo)?;
42    let (mut end_line, end_col) = line_and_byte_column(hi)?;
43
44    // Apply an offset so that code in doctests has correct line numbers.
45    // FIXME(#79417): Currently we have no way to offset doctest _columns_.
46    start_line = source_map.doctest_offset_line(&file.name, start_line);
47    end_line = source_map.doctest_offset_line(&file.name, end_line);
48
49    check_coverage_span(ffi::CoverageSpan {
50        file_id: file_id.as_u32(),
51        start_line: start_line as u32,
52        start_col: start_col as u32,
53        end_line: end_line as u32,
54        end_col: end_col as u32,
55    })
56}
57
58fn ensure_non_empty_span(
59    source_map: &SourceMap,
60    fn_cov_info: &FunctionCoverageInfo,
61    span: Span,
62) -> Option<Span> {
63    if !span.is_empty() {
64        return Some(span);
65    }
66
67    let lo = span.lo();
68    let hi = span.hi();
69
70    // The span is empty, so try to expand it to cover an adjacent '{' or '}',
71    // but only within the bounds of the body span.
72    let try_next = hi < fn_cov_info.body_span.hi();
73    let try_prev = fn_cov_info.body_span.lo() < lo;
74    if !(try_next || try_prev) {
75        return None;
76    }
77
78    source_map
79        .span_to_source(span, |src, start, end| try {
80            // Adjusting span endpoints by `BytePos(1)` is normally a bug,
81            // but in this case we have specifically checked that the character
82            // we're skipping over is one of two specific ASCII characters, so
83            // adjusting by exactly 1 byte is correct.
84            if try_next && src.as_bytes()[end] == b'{' {
85                Some(span.with_hi(hi + BytePos(1)))
86            } else if try_prev && src.as_bytes()[start - 1] == b'}' {
87                Some(span.with_lo(lo - BytePos(1)))
88            } else {
89                None
90            }
91        })
92        .ok()?
93}
94
95/// If `llvm-cov` sees a source region that is improperly ordered (end < start),
96/// it will immediately exit with a fatal error. To prevent that from happening,
97/// discard regions that are improperly ordered, or might be interpreted in a
98/// way that makes them improperly ordered.
99fn check_coverage_span(cov_span: ffi::CoverageSpan) -> Option<ffi::CoverageSpan> {
100    let ffi::CoverageSpan { file_id: _, start_line, start_col, end_line, end_col } = cov_span;
101
102    // Line/column coordinates are supposed to be 1-based. If we ever emit
103    // coordinates of 0, `llvm-cov` might misinterpret them.
104    let all_nonzero = [start_line, start_col, end_line, end_col].into_iter().all(|x| x != 0);
105    // Coverage mappings use the high bit of `end_col` to indicate that a
106    // region is actually a "gap" region, so make sure it's unset.
107    let end_col_has_high_bit_unset = (end_col & (1 << 31)) == 0;
108    // If a region is improperly ordered (end < start), `llvm-cov` will exit
109    // with a fatal error, which is inconvenient for users and hard to debug.
110    let is_ordered = (start_line, start_col) <= (end_line, end_col);
111
112    if all_nonzero && end_col_has_high_bit_unset && is_ordered {
113        Some(cov_span)
114    } else {
115        debug!(
116            ?cov_span,
117            ?all_nonzero,
118            ?end_col_has_high_bit_unset,
119            ?is_ordered,
120            "Skipping source region that would be misinterpreted or rejected by LLVM"
121        );
122        // If this happens in a debug build, ICE to make it easier to notice.
123        debug_assert!(false, "Improper source region: {cov_span:?}");
124        None
125    }
126}
rustc_codegen_llvm/coverageinfo/mapgen/spans.rs

rustc_codegen_llvm/coverageinfo/mapgen/
spans.rs
