Fix updating detailed completion for overloaded methods (#2633)

* For languages that allow method overloads, where the same method name
can be defined with different arguments (e.g. C++), the `label` of a
completion may be duplicated in the completions list, but the `detail`
should be different.
* Hence use the `detail` field, if available, to disambiguate between
completion items when updating them with the result of a
`completionItem/resolve`.

browser/src/Services/Completion/CompletionStore.ts

@@ -134,6 +134,16 @@ export const completionResultsReducer: Reducer<ICompletionResults> = (
             return {
                 ...state,
                 completions: state.completions.map(completion => {
+                    // Prefer `detail` field if available, to avoid splatting e.g. methods with
+                    // the same name but different signature.
+                    if (completion.detail && action.completionItemWithDetails.detail) {
+                        if (completion.detail === action.completionItemWithDetails.detail) {
+                            return action.completionItemWithDetails
+                        } else {
+                            return completion
+                        }
+                    }
+
                     if (completion.label === action.completionItemWithDetails.label) {
                         return action.completionItemWithDetails
                     } else {

browser/test/Services/Completion/CompletionStoreTests.ts

@@ -0,0 +1,66 @@
+import * as assert from "assert"
+import * as _ from "lodash"
+
+import { DefaultCompletionResults } from "./../../../src/Services/Completion/CompletionState"
+import { completionResultsReducer } from "./../../../src/Services/Completion/CompletionStore"
+
+describe("completionResultsReducer", () => {
+    let oldState: any
+
+    beforeEach(() => {
+        oldState = _.cloneDeep(DefaultCompletionResults)
+    })
+
+    describe("GET_COMPLETION_ITEM_DETAILS_RESULT", () => {
+        beforeEach(() => {
+            oldState.completions = [
+                { label: "other" },
+                { label: "matchme", detail: "matchme(signature)" },
+                { label: "matchme", detail: "other(signature)" },
+                { label: "matchme" },
+            ]
+        })
+
+        it("updates relevant items with detailed version by label field", () => {
+            const completionItemWithDetails = {
+                label: "matchme",
+            }
+
+            const newState = completionResultsReducer(oldState, {
+                type: "GET_COMPLETION_ITEM_DETAILS_RESULT",
+                completionItemWithDetails,
+            })
+
+            assert.deepStrictEqual(newState, {
+                ...oldState,
+                completions: [
+                    { label: "other" },
+                    completionItemWithDetails,
+                    completionItemWithDetails,
+                    completionItemWithDetails,
+                ],
+            })
+        })
+
+        it("updates relevant items with detailed version by detail field", () => {
+            const completionItemWithDetails = {
+                label: "matchme",
+                detail: "matchme(signature)",
+            }
+            const newState = completionResultsReducer(oldState, {
+                type: "GET_COMPLETION_ITEM_DETAILS_RESULT",
+                completionItemWithDetails,
+            })
+
+            assert.deepStrictEqual(newState, {
+                ...oldState,
+                completions: [
+                    { label: "other" },
+                    completionItemWithDetails,
+                    { label: "matchme", detail: "other(signature)" },
+                    completionItemWithDetails,
+                ],
+            })
+        })
+    })
+})