Roll back to the prev. branch on implicit else.

packages/istanbul-reports/lib/html/annotator.js

@@ -164,6 +164,14 @@ function annotateBranches(fileCoverage, structuredText) {
                     gt;
                 closeSpan = lt + '/span' + gt;
 
+                if (count === 0 && startLine === undefined && branchMeta[branchName].type === 'if') { 
+                    let prevMeta = metaArray[i - 1];
+                    startCol = prevMeta.start.column;
+                    endCol = prevMeta.end.column + 1;
+                    startLine = prevMeta.start.line;
+                    endLine = prevMeta.end.line;
+                }
+
                 if (count === 0 && structuredText[startLine]) {
                     //skip branches taken
                     if (endLine !== startLine) {
@@ -173,6 +181,7 @@ function annotateBranches(fileCoverage, structuredText) {
                     }
                     text = structuredText[startLine].text;
                     if (branchMeta[branchName].type === 'if') {
+                        debugger;
                         // 'if' is a special case
                         // since the else branch might not be visible, being non-existent
                         text.insertAt(

packages/istanbul-reports/test/fixtures/github-649.json

@@ -0,0 +1,127 @@
+{
+  "path": "/Users/benjamincoe/bcoe/istanbul-lib-instrument/src/index.js",
+  "statementMap": {
+    "0": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 9,
+        "column": 2
+      }
+    },
+    "1": {
+      "start": {
+        "line": 2,
+        "column": 10
+      },
+      "end": {
+        "line": 2,
+        "column": 11
+      }
+    },
+    "2": {
+      "start": {
+        "line": 4,
+        "column": 4
+      },
+      "end": {
+        "line": 6,
+        "column": 5
+      }
+    },
+    "3": {
+      "start": {
+        "line": 5,
+        "column": 6
+      },
+      "end": {
+        "line": 5,
+        "column": 12
+      }
+    },
+    "4": {
+      "start": {
+        "line": 8,
+        "column": 4
+      },
+      "end": {
+        "line": 8,
+        "column": 13
+      }
+    }
+  },
+  "fnMap": {
+    "0": {
+      "name": "(anonymous_0)",
+      "decl": {
+        "start": {
+          "line": 1,
+          "column": 16
+        },
+        "end": {
+          "line": 1,
+          "column": 17
+        }
+      },
+      "loc": {
+        "start": {
+          "line": 1,
+          "column": 28
+        },
+        "end": {
+          "line": 9,
+          "column": 1
+        }
+      },
+      "line": 1
+    }
+  },
+  "branchMap": {
+    "0": {
+      "loc": {
+        "start": {
+          "line": 4,
+          "column": 4
+        },
+        "end": {
+          "line": 6,
+          "column": 5
+        }
+      },
+      "type": "if",
+      "locations": [{
+          "start": {
+            "line": 4,
+            "column": 4
+          },
+          "end": {
+            "line": 6,
+            "column": 5
+          }
+        }, {
+          "start": {
+          },
+          "end": {
+          }
+        }
+      ],
+      "line": 4
+    }
+  },
+  "s": {
+    "0": 1,
+    "1": 1,
+    "2": 1,
+    "3": 1,
+    "4": 1
+  },
+  "f": {
+    "0": 1
+  },
+  "b": {
+    "0": [1, 0]
+  },
+  "hash": "edc1f904dd2d4c7214941451a07aabfc0aee6ec0"
+}

packages/istanbul-reports/test/html/annotator.js

@@ -81,5 +81,25 @@ describe('annotator', () => {
                 '<span class="fstat-no" title="function not covered" >  function test () {};</span>'
             );
         });
+
+      // see: https://github.com/istanbuljs/istanbuljs/issues/649
+      it('handles implicit else branches', () => {
+        const annotated = annotator(getFixture('github-649'), {
+            getSource() {
+                return `exports.testy = function () { 
+                  let a = 0;
+                
+                    if (!a) {
+                      a = 3;
+                    }
+                
+                    return a;
+                };`;
+            }
+        });
+        annotated.annotatedCode[3].should.equal(
+          '    <span class="missing-if-branch" title="else path not taken" >E</span>                if (!a) {'
+        );
+    });
     });
 });