Rollup merge of rust-lang#84582 - richkadel:issue-84561, r=tmandry

Vastly improves coverage spans for macros

Fixes: rust-lang#84561

This resolves problems where macros like `trace!(...)` would show zero coverage if tracing was disabled, and `assert_eq!(...)` would show zero coverage if the assertion did not fail, because only one coverage span was generated, for the branch.

This PR started with an idea that I could just drop branching blocks with same span as expanded macro. (See the fixed issue for more details.)

That did help, but it didn't resolve everything.

I also needed to add a span specifically for the macro name (plus `!`) to ensure the macro gets coverage even if it's internal expansion adds conditional branching blocks that are retained, and would otherwise drop the outer span. Now that outer span is _only_ the `(argument, list)`, which can safely be dropped now), because the macro name has its own span.

While testing, I also noticed the spanview debug output can cause an ICE on a function with no body. The
workaround for this is included in this PR (separate commit).

r? `````@tmandry`````
cc? `````@wesleywiser`````

compiler/rustc_mir/src/transform/coverage/tests.rs

@@ -1,6 +1,10 @@
 //! This crate hosts a selection of "unit tests" for components of the `InstrumentCoverage` MIR
 //! pass.
 //!
+//! ```shell
+//! ./x.py test --keep-stage 1 compiler/rustc_mir --test-args '--show-output coverage'
+//! ```
+//!
 //! The tests construct a few "mock" objects, as needed, to support the `InstrumentCoverage`
 //! functions and algorithms. Mocked objects include instances of `mir::Body`; including
 //! `Terminator`s of various `kind`s, and `Span` objects. Some functions used by or used on
@@ -679,10 +683,15 @@ fn test_make_bcb_counters() {
         let mut basic_coverage_blocks = graph::CoverageGraph::from_mir(&mir_body);
         let mut coverage_spans = Vec::new();
         for (bcb, data) in basic_coverage_blocks.iter_enumerated() {
-            if let Some(span) =
+            if let Some((span, expn_span)) =
                 spans::filtered_terminator_span(data.terminator(&mir_body), body_span)
             {
-                coverage_spans.push(spans::CoverageSpan::for_terminator(span, bcb, data.last_bb()));
+                coverage_spans.push(spans::CoverageSpan::for_terminator(
+                    span,
+                    expn_span,
+                    bcb,
+                    data.last_bb(),
+                ));
             }
         }
         let mut coverage_counters = counters::CoverageCounters::new(0);

compiler/rustc_mir/src/util/spanview.rs

@@ -99,7 +99,11 @@ where
     W: Write,
 {
     let def_id = body.source.def_id();
-    let body_span = hir_body(tcx, def_id).value.span;
+    let hir_body = hir_body(tcx, def_id);
+    if hir_body.is_none() {
+        return Ok(());
+    }
+    let body_span = hir_body.unwrap().value.span;
     let mut span_viewables = Vec::new();
     for (bb, data) in body.basic_blocks().iter_enumerated() {
         match spanview {
@@ -664,19 +668,16 @@ fn fn_span<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Span {
     let hir_id =
         tcx.hir().local_def_id_to_hir_id(def_id.as_local().expect("expected DefId is local"));
     let fn_decl_span = tcx.hir().span(hir_id);
-    let body_span = hir_body(tcx, def_id).value.span;
-    if fn_decl_span.ctxt() == body_span.ctxt() {
-        fn_decl_span.to(body_span)
+    if let Some(body_span) = hir_body(tcx, def_id).map(|hir_body| hir_body.value.span) {
+        if fn_decl_span.ctxt() == body_span.ctxt() { fn_decl_span.to(body_span) } else { body_span }
     } else {
-        // This probably occurs for functions defined via macros
-        body_span
+        fn_decl_span
     }
 }
 
-fn hir_body<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx rustc_hir::Body<'tcx> {
+fn hir_body<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<&'tcx rustc_hir::Body<'tcx>> {
     let hir_node = tcx.hir().get_if_local(def_id).expect("expected DefId is local");
-    let fn_body_id = hir::map::associated_body(hir_node).expect("HIR node is a function with body");
-    tcx.hir().body(fn_body_id)
+    hir::map::associated_body(hir_node).map(|fn_body_id| tcx.hir().body(fn_body_id))
 }
 
 fn escape_html(s: &str) -> String {

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.inner_items.txt

@@ -1,9 +1,9 @@
     1|       |#![allow(unused_assignments, unused_variables, dead_code)]
     2|       |
     3|      1|fn main() {
-    4|       |    // Initialize test constants in a way that cannot be determined at compile time, to ensure
-    5|       |    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
-    6|       |    // dependent conditions.
+    4|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    5|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    6|      1|    // dependent conditions.
     7|      1|    let is_true = std::env::args().len() == 1;
     8|      1|
     9|      1|    let mut countdown = 0;

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-84561.txt

@@ -0,0 +1,196 @@
+    1|       |// This demonstrated Issue #84561: function-like macros produce unintuitive coverage results.
+    2|       |
+    3|       |// expect-exit-status-101
+    4|     21|#[derive(PartialEq, Eq)]
+                                  ^0
+  ------------------
+  | <issue_84561::Foo as core::cmp::PartialEq>::eq:
+  |    4|     21|#[derive(PartialEq, Eq)]
+  ------------------
+  | Unexecuted instantiation: <issue_84561::Foo as core::cmp::PartialEq>::ne
+  ------------------
+    5|       |struct Foo(u32);
+    6|      1|fn test3() {
+    7|      1|    let is_true = std::env::args().len() == 1;
+    8|      1|    let bar = Foo(1);
+    9|      1|    assert_eq!(bar, Foo(1));
+   10|      1|    let baz = Foo(0);
+   11|      1|    assert_ne!(baz, Foo(1));
+   12|      1|    println!("{:?}", Foo(1));
+   13|      1|    println!("{:?}", bar);
+   14|      1|    println!("{:?}", baz);
+   15|      1|
+   16|      1|    assert_eq!(Foo(1), Foo(1));
+   17|      1|    assert_ne!(Foo(0), Foo(1));
+   18|      1|    assert_eq!(Foo(2), Foo(2));
+   19|      1|    let bar = Foo(0);
+   20|      1|    assert_ne!(bar, Foo(3));
+   21|      1|    assert_ne!(Foo(0), Foo(4));
+   22|      1|    assert_eq!(Foo(3), Foo(3), "with a message");
+                                             ^0
+   23|      1|    println!("{:?}", bar);
+   24|      1|    println!("{:?}", Foo(1));
+   25|      1|
+   26|      1|    assert_ne!(Foo(0), Foo(5), "{}", if is_true { "true message" } else { "false message" });
+                                             ^0                 ^0                      ^0
+   27|      1|    assert_ne!(
+   28|       |        Foo(0)
+   29|       |        ,
+   30|       |        Foo(5)
+   31|       |        ,
+   32|      0|        "{}"
+   33|      0|        ,
+   34|      0|        if
+   35|      0|        is_true
+   36|       |        {
+   37|      0|            "true message"
+   38|       |        } else {
+   39|      0|            "false message"
+   40|       |        }
+   41|       |    );
+   42|       |
+   43|      1|    let is_true = std::env::args().len() == 1;
+   44|      1|
+   45|      1|    assert_eq!(
+   46|      1|        Foo(1),
+   47|      1|        Foo(1)
+   48|      1|    );
+   49|      1|    assert_ne!(
+   50|      1|        Foo(0),
+   51|      1|        Foo(1)
+   52|      1|    );
+   53|      1|    assert_eq!(
+   54|      1|        Foo(2),
+   55|      1|        Foo(2)
+   56|      1|    );
+   57|      1|    let bar = Foo(1);
+   58|      1|    assert_ne!(
+   59|      1|        bar,
+   60|      1|        Foo(3)
+   61|      1|    );
+   62|      1|    if is_true {
+   63|      1|        assert_ne!(
+   64|      1|            Foo(0),
+   65|      1|            Foo(4)
+   66|      1|        );
+   67|       |    } else {
+   68|      0|        assert_eq!(
+   69|      0|            Foo(3),
+   70|      0|            Foo(3)
+   71|      0|        );
+   72|       |    }
+   73|      1|    if is_true {
+   74|      1|        assert_ne!(
+   75|       |            Foo(0),
+   76|       |            Foo(4),
+   77|      0|            "with a message"
+   78|       |        );
+   79|       |    } else {
+   80|      0|        assert_eq!(
+   81|       |            Foo(3),
+   82|       |            Foo(3),
+   83|      0|            "with a message"
+   84|       |        );
+   85|       |    }
+   86|      1|    assert_ne!(
+   87|      1|        if is_true {
+   88|      1|            Foo(0)
+   89|       |        } else {
+   90|      0|            Foo(1)
+   91|       |        },
+   92|       |        Foo(5)
+   93|       |    );
+   94|      1|    assert_ne!(
+   95|      1|        Foo(5),
+   96|      1|        if is_true {
+   97|      1|            Foo(0)
+   98|       |        } else {
+   99|      0|            Foo(1)
+  100|       |        }
+  101|       |    );
+  102|      1|    assert_ne!(
+  103|      1|        if is_true {
+  104|      1|            assert_eq!(
+  105|      1|                Foo(3),
+  106|      1|                Foo(3)
+  107|      1|            );
+  108|      1|            Foo(0)
+  109|       |        } else {
+  110|      0|            assert_ne!(
+  111|      0|                if is_true {
+  112|      0|                    Foo(0)
+  113|       |                } else {
+  114|      0|                    Foo(1)
+  115|       |                },
+  116|       |                Foo(5)
+  117|       |            );
+  118|      0|            Foo(1)
+  119|       |        },
+  120|       |        Foo(5),
+  121|      0|        "with a message"
+  122|       |    );
+  123|      1|    assert_eq!(
+  124|       |        Foo(1),
+  125|       |        Foo(3),
+  126|      1|        "this assert should fail"
+  127|       |    );
+  128|      0|    assert_eq!(
+  129|       |        Foo(3),
+  130|       |        Foo(3),
+  131|      0|        "this assert should not be reached"
+  132|       |    );
+  133|      0|}
+  134|       |
+  135|       |impl std::fmt::Debug for Foo {
+  136|       |    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+  137|      7|        write!(f, "try and succeed")?;
+                                                  ^0
+  138|      7|        Ok(())
+  139|      7|    }
+  140|       |}
+  141|       |
+  142|       |static mut DEBUG_LEVEL_ENABLED: bool = false;
+  143|       |
+  144|       |macro_rules! debug {
+  145|       |    ($($arg:tt)+) => (
+  146|       |        if unsafe { DEBUG_LEVEL_ENABLED } {
+  147|       |            println!($($arg)+);
+  148|       |        }
+  149|       |    );
+  150|       |}
+  151|       |
+  152|      1|fn test1() {
+  153|      1|    debug!("debug is enabled");
+                         ^0
+  154|      1|    debug!("debug is enabled");
+                         ^0
+  155|      1|    let _ = 0;
+  156|      1|    debug!("debug is enabled");
+                         ^0
+  157|      1|    unsafe {
+  158|      1|        DEBUG_LEVEL_ENABLED = true;
+  159|      1|    }
+  160|      1|    debug!("debug is enabled");
+  161|      1|}
+  162|       |
+  163|       |macro_rules! call_debug {
+  164|       |    ($($arg:tt)+) => (
+  165|      1|        fn call_print(s: &str) {
+  166|      1|            print!("{}", s);
+  167|      1|        }
+  168|       |
+  169|       |        call_print("called from call_debug: ");
+  170|       |        debug!($($arg)+);
+  171|       |    );
+  172|       |}
+  173|       |
+  174|      1|fn test2() {
+  175|      1|    call_debug!("debug is enabled");
+  176|      1|}
+  177|       |
+  178|      1|fn main() {
+  179|      1|    test1();
+  180|      1|    test2();
+  181|      1|    test3();
+  182|      1|}
+

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_crate.txt

@@ -3,9 +3,9 @@
     3|       |use std::fmt::Debug;
     4|       |
     5|      1|pub fn used_function() {
-    6|       |    // Initialize test constants in a way that cannot be determined at compile time, to ensure
-    7|       |    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
-    8|       |    // dependent conditions.
+    6|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    7|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    8|      1|    // dependent conditions.
     9|      1|    let is_true = std::env::args().len() == 1;
    10|      1|    let mut countdown = 0;
    11|      1|    if is_true {

src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_inline_crate.txt

@@ -5,9 +5,9 @@
     5|       |use std::fmt::Debug;
     6|       |
     7|      1|pub fn used_function() {
-    8|       |    // Initialize test constants in a way that cannot be determined at compile time, to ensure
-    9|       |    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
-   10|       |    // dependent conditions.
+    8|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    9|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+   10|      1|    // dependent conditions.
    11|      1|    let is_true = std::env::args().len() == 1;
    12|      1|    let mut countdown = 0;
    13|      1|    if is_true {
@@ -19,9 +19,9 @@
    18|       |
    19|       |#[inline(always)]
    20|      1|pub fn used_inline_function() {
-   21|       |    // Initialize test constants in a way that cannot be determined at compile time, to ensure
-   22|       |    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
-   23|       |    // dependent conditions.
+   21|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+   22|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+   23|      1|    // dependent conditions.
    24|      1|    let is_true = std::env::args().len() == 1;
    25|      1|    let mut countdown = 0;
    26|      1|    if is_true {