fix(coverage): merge duplicate reports (#8942)

Merging multiple runs isn't quite right because we 
rely on a 0 count to signal that a block hasn't been called.

Other tools like c8 expect this to be true as-well so we 
need to do our best to merge coverage files rather 
than duplicating them.

5 files changed, 89 insertions, 31 deletions

diff --git a/cli/tests/integration_tests.rs b/cli/tests/integration_tests.rs
index 9dc4df7cb..199172e2c 100644
--- a/cli/tests/integration_tests.rs
+++ b/cli/tests/integration_tests.rs
@@ -3330,6 +3330,12 @@ itest!(deno_test_run_run_coverage {
   exit_code: 0,
 });
 
+itest!(deno_test_run_combined_coverage {
+  args: "test --allow-all --coverage --unstable test_run_run_coverage.ts test_run_test_coverage.ts",
+  output: "test_run_combined_coverage.out",
+  exit_code: 0,
+});
+
 itest!(deno_lint {
   args: "lint --unstable lint/file1.js lint/file2.ts lint/ignored_file.ts",
   output: "lint/expected.out",
diff --git a/cli/tests/run_coverage.ts b/cli/tests/run_coverage.ts
index 098d463e8..d1443dfad 100644
--- a/cli/tests/run_coverage.ts
+++ b/cli/tests/run_coverage.ts
@@ -1,3 +1,3 @@
-import { returnsFoo2 } from "./subdir/mod1.ts";
+import { returnsHi } from "./subdir/mod1.ts";
 
-returnsFoo2();
+returnsHi();
diff --git a/cli/tests/test_run_combined_coverage.out b/cli/tests/test_run_combined_coverage.out
new file mode 100644
index 000000000..476e9adcc
--- /dev/null
+++ b/cli/tests/test_run_combined_coverage.out
@@ -0,0 +1,31 @@
+Check [WILDCARD]/tests/$deno$test.ts
+running 2 tests
+test spawn test ... Check [WILDCARD]/tests/run_coverage.ts
+ok ([WILDCARD])
+test spawn test ... Check [WILDCARD]/tests/$deno$test.ts
+running 1 tests
+test returnsFooSuccess ... ok ([WILDCARD])
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ([WILDCARD])
+
+ok ([WILDCARD])
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ([WILDCARD])
+
+cover [WILDCARD]/tests/run_coverage.ts ... 100.000% (3/3)
+cover [WILDCARD]/tests/subdir/mod1.ts ... 57.143% (8/14)
+   8 | export function printHello3() {
+   9 |     printHello2();
+  10 | }
+  11 | export function throwsError() {
+  12 |     throw Error("exception from mod1");
+  13 | }
+cover [WILDCARD]/tests/subdir/print_hello.ts ... 25.000% (1/4)
+   1 | export function printHello() {
+   2 |     console.log("Hello");
+   3 | }
+cover [WILDCARD]/tests/subdir/subdir2/mod2.ts ... 62.500% (5/8)
+   5 | export function printHello2() {
+   6 |     printHello();
+   7 | }
+cover [WILDCARD]/tests/test_coverage.ts ... 100.000% (5/5)
diff --git a/cli/tests/test_run_run_coverage.out b/cli/tests/test_run_run_coverage.out
index 15ea230ef..2f18020d3 100644
--- a/cli/tests/test_run_run_coverage.out
+++ b/cli/tests/test_run_run_coverage.out
@@ -1,16 +1,15 @@
-Check [WILDCARD]/$deno$test.ts
+Check [WILDCARD]/tests/$deno$test.ts
 running 1 tests
-test spawn test ... Check [WILDCARD]/run_coverage.ts
+test spawn test ... Check [WILDCARD]/tests/run_coverage.ts
 ok ([WILDCARD])
 
 test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out ([WILDCARD])
 
 cover [WILDCARD]/tests/run_coverage.ts ... 100.000% (3/3)
 cover [WILDCARD]/tests/subdir/mod1.ts ... 35.714% (5/14)
-   2 | export function returnsHi() {
-   3 |     return "Hi";
-   4 | }
------|-----
+   5 | export function returnsFoo2() {
+   6 |     return returnsFoo();
+   7 | }
    8 | export function printHello3() {
    9 |     printHello2();
   10 | }
@@ -21,7 +20,10 @@ cover [WILDCARD]/tests/subdir/print_hello.ts ... 25.000% (1/4)
    1 | export function printHello() {
    2 |     console.log("Hello");
    3 | }
-cover [WILDCARD]/tests/subdir/subdir2/mod2.ts ... 62.500% (5/8)
+cover [WILDCARD]/tests/subdir/subdir2/mod2.ts ... 25.000% (2/8)
+   2 | export function returnsFoo() {
+   3 |     return "Foo";
+   4 | }
    5 | export function printHello2() {
    6 |     printHello();
    7 | }
diff --git a/cli/tools/coverage.rs b/cli/tools/coverage.rs
index 53385b482..7cf98cab2 100644
--- a/cli/tools/coverage.rs
+++ b/cli/tools/coverage.rs
@@ -93,7 +93,7 @@ impl CoverageCollector {
 
 // TODO(caspervonb) all of these structs can and should be made private, possibly moved to
 // inspector::protocol.
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
 pub struct CoverageRange {
   pub start_offset: usize,
@@ -101,7 +101,7 @@ pub struct CoverageRange {
   pub count: usize,
 }
 
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
 pub struct FunctionCoverage {
   pub function_name: String,
@@ -109,7 +109,7 @@ pub struct FunctionCoverage {
   pub is_block_coverage: bool,
 }
 
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
 pub struct ScriptCoverage {
   pub script_id: String,
@@ -117,7 +117,7 @@ pub struct ScriptCoverage {
   pub functions: Vec<FunctionCoverage>,
 }
 
-#[derive(Debug, Serialize, Deserialize)]
+#[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
 pub struct Coverage {
   pub script_coverage: ScriptCoverage,
@@ -237,29 +237,48 @@ fn collect_coverages(dir: &PathBuf) -> Result<Vec<Coverage>, AnyError> {
   let entries = fs::read_dir(dir)?;
   for entry in entries {
     let json = fs::read_to_string(entry.unwrap().path())?;
-    let coverage: Coverage = serde_json::from_str(&json)?;
-
-    coverages.push(coverage);
-  }
-
-  // TODO(caspervonb) drain_filter would make this cleaner, its nightly at the moment.
-  if coverages.len() > 1 {
-    coverages.sort_by_key(|k| k.script_coverage.url.clone());
-
-    for i in (1..coverages.len() - 1).rev() {
-      if coverages[i].script_coverage.url
-        == coverages[i - 1].script_coverage.url
-      {
-        let current = coverages.remove(i);
-        let previous = &mut coverages[i - 1];
-
-        for function in current.script_coverage.functions {
-          previous.script_coverage.functions.push(function);
+    let new_coverage: Coverage = serde_json::from_str(&json)?;
+
+    let existing_coverage = coverages
+      .iter_mut()
+      .find(|x| x.script_coverage.url == new_coverage.script_coverage.url);
+
+    if let Some(existing_coverage) = existing_coverage {
+      for new_function in new_coverage.script_coverage.functions {
+        let existing_function = existing_coverage
+          .script_coverage
+          .functions
+          .iter_mut()
+          .find(|x| x.function_name == new_function.function_name);
+
+        if let Some(existing_function) = existing_function {
+          for new_range in new_function.ranges {
+            let existing_range =
+              existing_function.ranges.iter_mut().find(|x| {
+                x.start_offset == new_range.start_offset
+                  && x.end_offset == new_range.end_offset
+              });
+
+            if let Some(existing_range) = existing_range {
+              existing_range.count += new_range.count;
+            } else {
+              existing_function.ranges.push(new_range);
+            }
+          }
+        } else {
+          existing_coverage
+            .script_coverage
+            .functions
+            .push(new_function);
         }
       }
+    } else {
+      coverages.push(new_coverage);
     }
   }
 
+  coverages.sort_by_key(|k| k.script_coverage.url.clone());
+
   Ok(coverages)
 }