Fix #95 Stop parsing if an escape character precedes nothing

Signed-off-by: Remy Suen <[email protected]>

CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+## [Unreleased]
+### Fixed
+- prevent infinite loop when calculating semantic tokens if an escape character is not followed by any actual content ([#95](https://github.com/rcjsuen/dockerfile-language-service/issues/95))
+
 ## [0.7.2] - 2021-09-21
 ### Fixed
 - prevent infinite loop when calculating semantic tokens for an instruction with a keyword that spans multiple lines ([#94](https://github.com/rcjsuen/dockerfile-language-service/issues/94))

src/dockerSemanticTokens.ts

@@ -501,6 +501,11 @@ export class DockerSemanticTokens {
                         break;
                 }
             }
+
+            if (startOffset === -1) {
+                // we've processed the intermediate token but there is nothing of interest after it
+                return;
+            }
             const intermediateRange = {
                 start: this.document.positionAt(startOffset),
                 end: this.document.positionAt(endOffset),

test/dockerSemanticTokens.test.ts

@@ -1234,6 +1234,13 @@ describe("Dockerfile Semantic Token tests", () => {
                 assertEdit(tokens.data, SemanticTokenTypes.keyword, 10, 1, 0, 1);
                 assertEdit(tokens.data, SemanticTokenTypes.keyword, 15, 1, 0, 3);
             });
+
+            it("splits into nothing", () => {
+                const tokens = computeSemanticTokens("R\\ \n");
+                assert.strictEqual(10, tokens.data.length);
+                assertEdit(tokens.data, SemanticTokenTypes.keyword, 0, 0, 0, 1);
+                assertEdit(tokens.data, SemanticTokenTypes.macro, 5, 0, 1, 1);
+            });
         });
 
         describe("split arguments", () => {