test runner: Could not report code coverage (regression)

[yume-chan]

Version

v22.6.0

Platform

Linux f5d6c39aef47 5.15.153.1-microsoft-standard-WSL2 #1 SMP Fri Mar 29 23:14:13 UTC 2024 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

Because the cryptic error message, I can't narrow the repro down further.

npm i -g pnpm
git clone --depth 1 https://github.com/yume-chan/ya-webadb.git
cd ya-webadb/
pnpm i
pnpm build
cd libraries/struct
npx tsc -b tsconfig.test.json
node --enable-source-maps --experimental-test-coverage --test esm/struct.spec.js

How often does it reproduce? Is there a required condition?

100%

What is the expected behavior? Why is that the expected behavior?

Reports code coverage. It worked in v20.15.0

What do you see instead?

Begin with v20.16.0, it outputs:

ℹ Warning: Could not report code coverage. TypeError: Cannot read properties of undefined (reading 'line')

Additional information

No response

[avivkeller]

This is an issue that is caused by the tsc compilation. If I recall correctly, a fix is not planned, but I might be wrong.

CC @nodejs/test_runner to be sure

[cjihrig]

This doesn't seem like a good error for users to encounter. We should improve it.

[avivkeller]

Thanks for taking a look! Sorry for my misjudgment.

[avivkeller]

Related:
#52775
#53719 (comment)
#51392 (comment)

nodejs/help#4325
#51552

[avivkeller]

FWIW I couldn't reproduce using the following code:

interface Person {
    firstName: string;
    lastName: string;
    age: number;
    greet(): string;
}

class Student implements Person {
    firstName: string;
    lastName: string;
    age: number;
    grade: string;

    constructor(firstName: string, lastName: string, age: number, grade: string) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
        this.grade = grade;
    }

    greet(): string {
        return `Hello, my name is ${this.firstName} ${this.lastName} and I am ${this.age} years old.`;
    }

    getGrade(): string {
        return `I am in grade ${this.grade}.`;
    }
}

let student1 = new Student('John', 'Doe', 20, 'Junior');

console.log(student1.greet());
console.log(student1.getGrade());

npx tsc source.ts
node --enable-source-maps --experimental-test-coverage --test source.js

But I'll keep trying to find a minimal reproduction

[avivkeller]

@yume-chan could you provide the compiled file + sourcemap?

[yume-chan]

I found a minimal repro. It just needs enough lines:

index.ts

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function a() {
  console.log(1);
}
a();

index.js

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function a() {
    console.log(1);
}
a();
//# sourceMappingURL=index.js.map

index.js.map

{"version":3,"file":"index.js","sourceRoot":"","sources":["index.ts"],"names":[],"mappings":"AAAA,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,CAAC,CAAC;AACF,SAAS,CAAC;IACR,OAAO,CAAC,GAAG,CAAC,CAAC,CAAC,CAAC;AACjB,CAAC;AACD,CAAC,EAAE,CAAC"}

Any source map visualizer will tell you the generated source map is definitely correct: link

Output:

> node --enable-source-maps --experimental-test-coverage --test "index.js"                              
1
✔ D:\dev\sandbox\node-source-map\index.js (90.0243ms)
ℹ Warning: Could not report code coverage. TypeError: Cannot read properties of undefined (reading 'line')
ℹ tests 1
ℹ suites 0
ℹ pass 1
ℹ fail 0
ℹ cancelled 0
ℹ skipped 0
ℹ todo 0
ℹ duration_ms 95.1846

---

Node.js source map module calculates line lengths excluding the line break character:

node/lib/internal/source_map/source_map_cache.js

Lines 228 to 249 in 90dea9e

	// Cache the length of each line in the file that a source map was extracted
	// from. This allows translation from byte offset V8 coverage reports,
	// to line/column offset Source Map V3.
	function lineLengths(content) {
	const contentLength = content.length;
	const output = [];
	let lineLength = 0;
	for (let i = 0; i < contentLength; i++, lineLength++) {
	const codePoint = StringPrototypeCodePointAt(content, i);
	// We purposefully keep \r as part of the line-length calculation, in
	// cases where there is a \r\n separator, so that this can be taken into
	// account in coverage calculations.
	// codepoints for \n (new line), \u2028 (line separator) and \u2029 (paragraph separator)
	if (codePoint === 10 || codePoint === 0x2028 || codePoint === 0x2029) {
	ArrayPrototypePush(output, lineLength);
	lineLength = -1; // To not count the matched codePoint such as \n character
	}
	}
	ArrayPrototypePush(output, lineLength);
	return output;
	}

The line lengths are then converted to line offsets, but it's done incorrectly:

node/lib/internal/test_runner/coverage.js

Lines 342 to 346 in 90dea9e

	const executedLines = ArrayPrototypeMap(lineLengths, (length, i) => {
	const coverageLine = new CoverageLine(i + 1, offset, null, length);
	offset += length;
	return coverageLine;
	});

It didn't add the line break characters back, so after each line the offset is short by 1.

It then got matched with correct offsets:

node/lib/internal/test_runner/coverage.js

Line 363 in 90dea9e

const { lines } = mapRangeToLines(ranges[k], executedLines);

So after enough lines, mapRangeToLines returns an empty lines array, causing this line to throw error:

node/lib/internal/test_runner/coverage.js

Line 366 in 90dea9e

.findEntry(lines[0].line - 1, MathMax(0, startOffset - lines[0].startOffset));

---

Fix:

--- a/lib/internal/test_runner/coverage.js
+++ b/lib/internal/test_runner/coverage.js
@@ -340,8 +340,8 @@ class TestCoverage {
       const { data, lineLengths } = sourceMapCache[url];
       let offset = 0;
       const executedLines = ArrayPrototypeMap(lineLengths, (length, i) => {
-        const coverageLine = new CoverageLine(i + 1, offset, null, length);
-        offset += length;
+        const coverageLine = new CoverageLine(i + 1, offset, null, length + 1);
+        offset += length + 1;
         return coverageLine;
       });
       if (data.sourcesContent != null) {

[martinssonj]

Thanks for investigating this issue. I also experience the same problem.

[cjihrig]

@yume-chan thanks for looking into this. Would you like to open a PR?