Fix off-by-one error in code fence transform (#12540)

The code fence transform was including contents after the final END directive twice. That was not covered by the tests, because none of the examples contained any content after the final END directive, and concatenating the empty string twice does not produce an observable difference in the test results.

This bug was due to an off-by-one error in the loop of the multiSplice function. The error has been fixed, and more test cases have been added.

development/build/transforms/remove-fenced-code.js

@@ -408,7 +408,9 @@ function multiSplice(toSplice, splicingIndices) {
   // pushes the substring between each "end" index and the next "begin" index
   // to the array of retained substrings.
   if (splicingIndices.length > 2) {
-    for (let i = 1; i < splicingIndices.length; i += 2) {
+    // Note the boundary index of "splicingIndices.length - 1". This loop must
+    // not iterate over the last element of the array.
+    for (let i = 1; i < splicingIndices.length - 1; i += 2) {
       retainedSubstrings.push(
         toSplice.substring(splicingIndices[i], splicingIndices[i + 1]),
       );

development/build/transforms/remove-fenced-code.test.js

@@ -201,6 +201,14 @@ describe('build/transforms/remove-fenced-code', () => {
           ),
         ).toStrictEqual(testData.validOutputs[buildType]);
 
+        expect(
+          removeFencedCode(
+            mockFileName,
+            buildType,
+            testData.validInputs.extraContentWithFences,
+          ),
+        ).toStrictEqual(testData.validOutputsWithExtraContent[buildType]);
+
         // Ensure that the minimal input template is in fact valid
         const minimalInput = getMinimalFencedCode(buildType);
         expect(
@@ -216,6 +224,17 @@ describe('build/transforms/remove-fenced-code', () => {
             testData.validInputs.withoutFences,
           ),
         ).toStrictEqual([testData.validInputs.withoutFences, false]);
+
+        expect(
+          removeFencedCode(
+            mockFileName,
+            buildType,
+            testData.validInputs.extraContentWithoutFences,
+          ),
+        ).toStrictEqual([
+          testData.validInputs.extraContentWithoutFences,
+          false,
+        ]);
       });
     });
 
@@ -611,6 +630,43 @@ Conditionally_Included
        ///: END:ONLY_INCLUDE_IN
 `,
 
+      extraContentWithFences: `
+///: BEGIN:ONLY_INCLUDE_IN(flask,beta)
+Conditionally_Included
+///: END:ONLY_INCLUDE_IN
+  Always_Included
+Always_Included
+   Always_Included
+Always_Included
+  ///: BEGIN:ONLY_INCLUDE_IN(flask,beta)
+  Conditionally_Included
+
+  Conditionally_Included
+  Conditionally_Included
+  ///: END:ONLY_INCLUDE_IN
+Always_Included
+
+Always_Included
+   Always_Included
+          ///: BEGIN:ONLY_INCLUDE_IN(flask)
+
+  Conditionally_Included
+    Conditionally_Included
+       ///: END:ONLY_INCLUDE_IN
+Always_Included
+   Always_Included
+Always_Included
+
+///: BEGIN:ONLY_INCLUDE_IN(flask)
+  Conditionally_Included
+Conditionally_Included
+
+       ///: END:ONLY_INCLUDE_IN
+    Always_Included
+      Always_Included
+Always_Included
+`,
+
       withoutFences: `
   Always_Included
 Always_Included
@@ -624,6 +680,24 @@ Always_Included
    Always_Included
 Always_Included
 
+`,
+
+      extraContentWithoutFences: `
+  Always_Included
+Always_Included
+   Always_Included
+Always_Included
+Always_Included
+
+Always_Included
+   Always_Included
+Always_Included
+   Always_Included
+Always_Included
+
+    Always_Included
+      Always_Included
+Always_Included
 `,
     },
 
@@ -651,6 +725,38 @@ Always_Included
    Always_Included
 Always_Included
 
+`,
+        true,
+      ],
+    },
+
+    validOutputsWithExtraContent: {
+      beta: [
+        `
+///: BEGIN:ONLY_INCLUDE_IN(flask,beta)
+Conditionally_Included
+///: END:ONLY_INCLUDE_IN
+  Always_Included
+Always_Included
+   Always_Included
+Always_Included
+  ///: BEGIN:ONLY_INCLUDE_IN(flask,beta)
+  Conditionally_Included
+
+  Conditionally_Included
+  Conditionally_Included
+  ///: END:ONLY_INCLUDE_IN
+Always_Included
+
+Always_Included
+   Always_Included
+Always_Included
+   Always_Included
+Always_Included
+
+    Always_Included
+      Always_Included
+Always_Included
 `,
         true,
       ],
@@ -659,5 +765,14 @@ Always_Included
 
   data.validOutputs.flask = [data.validInputs.withFences, false];
   data.validOutputs.main = [data.validInputs.withoutFences, true];
+
+  data.validOutputsWithExtraContent.flask = [
+    data.validInputs.extraContentWithFences,
+    false,
+  ];
+  data.validOutputsWithExtraContent.main = [
+    data.validInputs.extraContentWithoutFences,
+    true,
+  ];
   return deepFreeze(data);
 }