coverage. Warn about too many test vectors

Author: zhuyunxing

compiler/rustc_mir_transform/messages.ftl

@@ -9,6 +9,8 @@ mir_transform_const_mut_borrow = taking a mutable reference to a `const` item
 .note2 = the mutable reference will refer to this temporary, not the original `const` item
 .note3 = mutable reference created due to call to this method
 
+mir_transform_exceeds_mcdc_test_vector_limit = number of total test vectors in one function will exceed limit ({$max_num_test_vectors}) if this decision is instrumented, so MC/DC analysis ignores it
+
 mir_transform_ffi_unwind_call = call to {$foreign->
  [true] foreign function
  *[false] function pointer

compiler/rustc_mir_transform/src/coverage/mappings.rs

@@ -15,6 +15,7 @@ use crate::coverage::ExtractedHirInfo;
 usecrate::coverage::graph::{BasicCoverageBlock,CoverageGraph,START_BCB};
 usecrate::coverage::spans::extract_refined_covspans;
 usecrate::coverage::unexpand::unexpand_into_body_span;
+usecrate::errors::MCDCExceedsTestVectorLimit;
 
 /// Associates an ordinary executable code span with its corresponding BCB.
 #[derive(Debug)]
@@ -108,6 +109,7 @@ pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
 
 extract_mcdc_mappings(
  mir_body,
+ tcx,
  hir_info.body_span,
  basic_coverage_blocks,
 &mut mcdc_bitmap_bits,
@@ -239,6 +241,7 @@ pub(super) fn extract_branch_pairs(
 
 pub(super)fnextract_mcdc_mappings(
 mir_body:&mir::Body<'_>,
+tcx:TyCtxt<'_>,
 body_span:Span,
 basic_coverage_blocks:&CoverageGraph,
 mcdc_bitmap_bits:&mutusize,
@@ -312,7 +315,10 @@ pub(super) fn extract_mcdc_mappings(
 }
 let num_test_vectors = calc_test_vectors_index(&mut branch_mappings);
 letSome(bitmap_idx) = get_bitmap_idx(num_test_vectors)else{
-// TODO warn about bitmap
+ tcx.dcx().emit_warn(MCDCExceedsTestVectorLimit{
+span: decision_span,
+max_num_test_vectors:MCDC_MAX_BITMAP_SIZE,
+});
  mcdc_degraded_branches.extend(branch_mappings);
 returnNone;
 };

compiler/rustc_mir_transform/src/errors.rs

@@ -89,6 +89,14 @@ pub(crate) struct FnItemRef {
 pubident:String,
 }
 
+#[derive(Diagnostic)]
+#[diag(mir_transform_exceeds_mcdc_test_vector_limit)]
+pub(crate)structMCDCExceedsTestVectorLimit{
+#[primary_span]
+pub(crate)span:Span,
+pub(crate)max_num_test_vectors:usize,
+}
+
 pub(crate)structMustNotSupend<'a,'tcx>{
 pubtcx:TyCtxt<'tcx>,
 pubyield_sp:Span,