Don’t call getEffectiveLines during tsc emit at all

microsoft · andrewbranch · Mar 19, 2020 · Feb 6, 2020 · Feb 7, 2020 · Feb 7, 2020
commit ac768d030290290ade1a951624fb6f7d76521666
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
@@ -4323,12 +4323,15 @@ namespace ts {
                     return 0;
                 }
                 else if (!nodeIsSynthesized(previousNode) && !nodeIsSynthesized(nextNode) && previousNode.parent === nextNode.parent) {
-                    return getEffectiveLines(
-                        includeComments => getLinesBetweenRangeEndAndRangeStart(
-                            previousNode,
-                            nextNode,
-                            currentSourceFile!,
-                            includeComments));
+                    if (preserveSourceNewlines) {
+                        return getEffectiveLines(
+                            includeComments => getLinesBetweenRangeEndAndRangeStart(
+                                previousNode,
+                                nextNode,
+                                currentSourceFile!,
+                                includeComments));
+                    }
+                    return rangeEndIsOnSameLineAsRangeStart(previousNode, nextNode, currentSourceFile!) ? 0 : 1;
                 }
                 else if (synthesizedNodeStartsOnNewLine(previousNode, format) || synthesizedNodeStartsOnNewLine(nextNode, format)) {
                     return 1;
@@ -4371,11 +4374,9 @@ namespace ts {
         }
 
         function getEffectiveLines(getLineDifference: (includeComments: boolean) => number) {
-            // If 'preserveSourceNewlines' is disabled, skip the more accurate check that might require
-            // querying for source positions twice.
-            if (!preserveSourceNewlines) {
-                return Math.min(1, getLineDifference(/*includeComments*/ false));
-            }
+            // If 'preserveSourceNewlines' is disabled, we should never call this function
+            // because it could be more expensive than alternative approximations.
+            Debug.assert(!!preserveSourceNewlines);
             // We start by measuring the line difference from a position to its adjacent comments,
             // so that this is counted as a one-line difference, not two:
             //
@@ -4424,12 +4425,15 @@ namespace ts {
             }
 
             if (!nodeIsSynthesized(parent) && !nodeIsSynthesized(node1) && !nodeIsSynthesized(node2)) {
-                return getEffectiveLines(
-                    includeComments => getLinesBetweenRangeEndAndRangeStart(
-                        node1,
-                        node2,
-                        currentSourceFile!,
-                        includeComments));
+                if (preserveSourceNewlines) {
+                    return getEffectiveLines(
+                        includeComments => getLinesBetweenRangeEndAndRangeStart(
+                            node1,
+                            node2,
+                            currentSourceFile!,
+                            includeComments));
+                }
+                return rangeEndIsOnSameLineAsRangeStart(node1, node2, currentSourceFile!) ? 0 : 1;
             }
 
             return 0;