fix --pretty output when context is multi-line

Fixes #22097

src/compiler/program.ts

@@ -289,8 +289,8 @@ namespace ts {
                     gutterWidth = Math.max(ellipsis.length, gutterWidth);
                 }
 
-                context += host.getNewLine();
                 for (let i = firstLine; i <= lastLine; i++) {
+                    context += host.getNewLine();
                     // If the error spans over 5 lines, we'll only show the first 2 and last 2 lines,
                     // so we'll skip ahead to the second-to-last line.
                     if (hasMoreThanFiveLines && firstLine + 1 < i && i < lastLine - 1) {

tests/baselines/reference/multiLineContextDiagnosticWithPretty.errors.txt

@@ -0,0 +1,24 @@
+tests/cases/compiler/multiLineContextDiagnosticWithPretty.ts:2:5 - error TS2322: Type '{ a: { b: string; }; }' is not assignable to type '{ c: string; }'.
+  Object literal may only specify known properties, and 'a' does not exist in type '{ c: string; }'.
+
+2     a: {
+      ~~~~
+3         b: '',
+  ~~~~~~~~~~~~~~
+4     }
+  ~~~~~
+
+
+
+==== tests/cases/compiler/multiLineContextDiagnosticWithPretty.ts (1 errors) ====
+    const x: {c: string} = {
+        a: {
+        ~~~~
+            b: '',
+    ~~~~~~~~~~~~~~
+        }
+    ~~~~~
+!!! error TS2322: Type '{ a: { b: string; }; }' is not assignable to type '{ c: string; }'.
+!!! error TS2322:   Object literal may only specify known properties, and 'a' does not exist in type '{ c: string; }'.
+    };
+    

tests/baselines/reference/multiLineContextDiagnosticWithPretty.js

@@ -0,0 +1,14 @@
+//// [multiLineContextDiagnosticWithPretty.ts]
+const x: {c: string} = {
+    a: {
+        b: '',
+    }
+};
+
+
+//// [multiLineContextDiagnosticWithPretty.js]
+var x = {
+    a: {
+        b: ''
+    }
+};

tests/baselines/reference/multiLineContextDiagnosticWithPretty.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/multiLineContextDiagnosticWithPretty.ts ===
+const x: {c: string} = {
+>x : Symbol(x, Decl(multiLineContextDiagnosticWithPretty.ts, 0, 5))
+>c : Symbol(c, Decl(multiLineContextDiagnosticWithPretty.ts, 0, 10))
+
+    a: {
+>a : Symbol(a, Decl(multiLineContextDiagnosticWithPretty.ts, 0, 24))
+
+        b: '',
+>b : Symbol(b, Decl(multiLineContextDiagnosticWithPretty.ts, 1, 8))
+    }
+};
+

tests/baselines/reference/multiLineContextDiagnosticWithPretty.types

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/multiLineContextDiagnosticWithPretty.ts ===
+const x: {c: string} = {
+>x : { c: string; }
+>c : string
+>{    a: {        b: '',    }} : { a: { b: string; }; }
+
+    a: {
+>a : { b: string; }
+>{        b: '',    } : { b: string; }
+
+        b: '',
+>b : string
+>'' : ""
+    }
+};
+

tests/cases/compiler/multiLineContextDiagnosticWithPretty.ts

@@ -0,0 +1,6 @@
+// @pretty: true
+const x: {c: string} = {
+    a: {
+        b: '',
+    }
+};