From 3db3aa468c02fd699760cc4d96f044b42e31be90 Mon Sep 17 00:00:00 2001
From: Josh Goldberg <josh@codecademy.com>
Date: Sun, 28 Mar 2021 22:52:52 -0400
Subject: [PATCH 1/2] fix(eslint-plugin): always ignore assignments in
 no-unnecessary-type-assertion

---
 .../rules/no-unnecessary-type-assertion.ts    | 25 ++++++++++---------
 .../no-unnecessary-type-assertion.test.ts     | 12 +++++----
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index 5ae12f5a33d..8da01bff146 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -137,19 +137,20 @@ export default util.createRule<Options, MessageIds>({
       TSNonNullExpression(node): void {
         if (
           node.parent?.type === AST_NODE_TYPES.AssignmentExpression &&
-          node.parent?.operator === '=' &&
-          node.parent.left === node
+          node.parent.operator === '='
         ) {
-          context.report({
-            node,
-            messageId: 'contextuallyUnnecessary',
-            fix(fixer) {
-              return fixer.removeRange([
-                node.expression.range[1],
-                node.range[1],
-              ]);
-            },
-          });
+          if (node.parent.left === node) {
+            context.report({
+              node,
+              messageId: 'contextuallyUnnecessary',
+              fix(fixer) {
+                return fixer.removeRange([
+                  node.expression.range[1],
+                  node.range[1],
+                ]);
+              },
+            });
+          }
           return;
         }
 
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
index 65d0874dd3a..0f530622b9a 100644
--- a/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
@@ -202,6 +202,12 @@ let a: { b?: string } | undefined;
 a!.b = '';
       `,
     },
+    `
+let value: number | undefined;
+let values: number[] = [];
+
+value = values.pop()!;
+    `,
   ],
 
   invalid: [
@@ -477,14 +483,10 @@ y! = 0;
       output: `
 let x: number | undefined;
 let y: number | undefined;
-y = x;
+y = x!;
 y = 0;
       `,
       errors: [
-        {
-          messageId: 'contextuallyUnnecessary',
-          line: 4,
-        },
         {
           messageId: 'contextuallyUnnecessary',
           line: 5,

From db0e0260f1490c64465dfe1ab59e89beeec15598 Mon Sep 17 00:00:00 2001
From: Josh Goldberg <me@joshuakgoldberg.com>
Date: Sun, 4 Apr 2021 22:53:32 -0400
Subject: [PATCH 2/2] Update
 packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts

Co-authored-by: Brad Zacher <brad.zacher@gmail.com>
---
 .../eslint-plugin/src/rules/no-unnecessary-type-assertion.ts  | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index 8da01bff146..9b8d2ba76f5 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -151,6 +151,10 @@ export default util.createRule<Options, MessageIds>({
               },
             });
           }
+          // for all other = assignments we ignore non-null checks
+          // this is because non-null assertions can change the type-flow of the code
+          // so whilst they might be unnecessary for the assignment - they are necessary
+          // for following code
           return;
         }