feat (coverage): Load branch coverage from coverage files (#389)

This commit teaches the LCOV parser to also read branch coverage data.

Works towards #362

src/test-explorer/lcov_parser.ts

@@ -48,6 +48,8 @@ export function parseLcov(
   class FileCoverageInfo {
     functionsByLine: Map<number, vscode.DeclarationCoverage> = new Map();
     lineCoverage: Map<number, vscode.StatementCoverage> = new Map();
+    coverageByLineAndBranch: Map<number, Map<string, vscode.BranchCoverage>> =
+      new Map();
   }
   const infosByFile: Map<string, FileCoverageInfo> = new Map();
   for (const block of lcov.split(/end_of_record(\n|$)/)) {
@@ -191,12 +193,54 @@ export function parseLcov(
           // Ignored. Reconstructed from DA entries
           break;
         case "BRDA": {
-          // branch coverage: <line_number>,[<exception>]<block>,<branch>,<taken>
+          // branch coverage: <line_number>,[<exception>]<block>,<branch>,<hitCount>
+          // Note that the <branch> might contain commas, which requires being
+          // a bit careful while parsing.
           const match = value.match(/(\d+),(e?)(\d+),(.+)/);
           if (!match) {
             throw new Error(`Invalid FNDA entry`);
           }
-          // TODO: Add support for branch coverage
+          const lineNumber = Number.parseInt(match[1], 10) - 1;
+          if (lineNumber < 0) {
+            throw new Error("Negative line number in DA entry");
+          }
+          const isException = match[2] === "e";
+          const blockId = Number.parseInt(match[3], 10);
+          const rest = match[4];
+          const commaOffset = rest.lastIndexOf(",");
+          if (commaOffset === undefined) {
+            throw new Error(`Invalid FNDA entry`);
+          }
+          const label = rest.substring(0, commaOffset);
+          const hitCountStr = rest.substring(commaOffset + 1);
+          const hitCount =
+            hitCountStr === "-" ? 0 : Number.parseInt(hitCountStr, 10);
+          if (hitCount < 0) {
+            throw new Error("Negative hit count in DA entry");
+          }
+
+          if (info === undefined) {
+            throw new Error(`Missing filename`);
+          }
+
+          // We don't want to display coverage for exception edges.
+          if (isException) break;
+
+          // Insert into `branchByLineAndBranch`
+          if (!info.coverageByLineAndBranch.has(lineNumber)) {
+            info.coverageByLineAndBranch.set(lineNumber, new Map());
+          }
+          const coverageByBranch = info.coverageByLineAndBranch.get(lineNumber);
+          const branchId = `${blockId}:${label}`;
+          if (!coverageByBranch.has(branchId)) {
+            coverageByBranch.set(
+              branchId,
+              new vscode.BranchCoverage(0, undefined, label),
+            );
+          }
+          const branchCoverage = coverageByBranch.get(branchId);
+          assert(typeof branchCoverage.executed == "number");
+          branchCoverage.executed += hitCount;
           break;
         }
         case "BRF": // branches found
@@ -216,7 +260,16 @@ export function parseLcov(
       Array.from(info.functionsByLine.values()),
     );
     detailedCoverage = detailedCoverage.concat(
-      Array.from(info.lineCoverage.values()),
+      Array.from(info.lineCoverage.values()).map((c) => {
+        assert("line" in c.location);
+        const branchCoverage = info.coverageByLineAndBranch.get(
+          c.location.line,
+        );
+        if (branchCoverage) {
+          c.branches = Array.from(branchCoverage.values());
+        }
+        return c;
+      }),
     );
     fileCoverages.push(
       BazelFileCoverage.fromDetails(

test/lcov_parser.test.ts

@@ -89,7 +89,9 @@ describe("The lcov parser", () => {
       assert.strictEqual(fileCov.statementCoverage.covered, 11);
     });
     it("branch coverage", () => {
-      assert(fileCov.branchCoverage === undefined);
+      assert(fileCov.branchCoverage !== undefined);
+      assert.strictEqual(fileCov.branchCoverage.total, 6);
+      assert.strictEqual(fileCov.branchCoverage.covered, 3);
     });
     it("function coverage details", () => {
       const initFunc = getFunctionByLine(fileCov, 24);
@@ -109,6 +111,12 @@ describe("The lcov parser", () => {
       assert.equal(getLineCoverageForLine(fileCov, 38).executed, 0);
       assert.equal(getLineCoverageForLine(fileCov, 40).executed, 1);
     });
+    it("branch coverage data", () => {
+      const branchCoverage = getLineCoverageForLine(fileCov, 37).branches;
+      assert.equal(branchCoverage.length, 2);
+      assert.equal(branchCoverage[0].executed, 1);
+      assert.equal(branchCoverage[1].executed, 0);
+    });
   });
 
   describe("parses C++ coverage data", () => {
@@ -128,7 +136,9 @@ describe("The lcov parser", () => {
       assert.strictEqual(fileCov.statementCoverage.covered, 505);
     });
     it("branch coverage", () => {
-      assert(fileCov.branchCoverage === undefined);
+      assert(fileCov.branchCoverage !== undefined);
+      assert.strictEqual(fileCov.branchCoverage.total, 2560);
+      assert.strictEqual(fileCov.branchCoverage.covered, 843);
     });
     it("function coverage details", () => {
       const initFunc = getFunctionByLine(fileCov, 71);
@@ -141,6 +151,14 @@ describe("The lcov parser", () => {
       assert.equal(getLineCoverageForLine(fileCov, 178).executed, 0);
       assert.equal(getLineCoverageForLine(fileCov, 193).executed, 4);
     });
+    it("branch coverage data", () => {
+      const branchCoverage = getLineCoverageForLine(fileCov, 479).branches;
+      assert.equal(branchCoverage.length, 2);
+      assert.equal(branchCoverage[0].executed, 1);
+      assert.equal(branchCoverage[1].executed, 0);
+      const branchCoverage2 = getLineCoverageForLine(fileCov, 481).branches;
+      assert.equal(branchCoverage2.length, 12);
+    });
   });
 
   describe("parses Rust coverage data", () => {
@@ -161,6 +179,8 @@ describe("The lcov parser", () => {
       assert.strictEqual(fileCov.statementCoverage.covered, 426);
     });
     it("branch coverage", () => {
+      // Rust has no branch coverage data, as of writing this test case.
+      // Also see https://github.com/rust-lang/rust/issues/79649
       assert(fileCov.branchCoverage === undefined);
     });
     it("function coverage details", () => {
@@ -194,6 +214,7 @@ describe("The lcov parser", () => {
       assert.strictEqual(fileCov.statementCoverage.covered, 133);
     });
     it("branch coverage", () => {
+      // Go has no branch coverage data.
       assert(fileCov.branchCoverage === undefined);
     });
     it("line coverage details", () => {