3 files changed, 70 insertions, 1 deletions

diff --git a/editors/code/src/test/fixtures/rust-diagnostics/error/E0308.json b/editors/code/src/test/fixtures/rust-diagnostics/error/E0308.json
new file mode 100644
index 000000000..fb23824a3
--- /dev/null
+++ b/editors/code/src/test/fixtures/rust-diagnostics/error/E0308.json
@@ -0,0 +1,33 @@
+{
+    "message": "mismatched types",
+    "code": {
+        "code": "E0308",
+        "explanation": "\nThis error occurs when the compiler was unable to infer the concrete type of a\nvariable. It can occur for several cases, the most common of which is a\nmismatch in the expected type that the compiler inferred for a variable's\ninitializing expression, and the actual type explicitly assigned to the\nvariable.\n\nFor example:\n\n```compile_fail,E0308\nlet x: i32 = \"I am not a number!\";\n//     ~~~   ~~~~~~~~~~~~~~~~~~~~\n//      |             |\n//      |    initializing expression;\n//      |    compiler infers type `&str`\n//      |\n//    type `i32` assigned to variable `x`\n```\n"
+    },
+    "level": "error",
+    "spans": [
+        {
+            "file_name": "runtime/compiler_support.rs",
+            "byte_start": 1589,
+            "byte_end": 1594,
+            "line_start": 48,
+            "line_end": 48,
+            "column_start": 65,
+            "column_end": 70,
+            "is_primary": true,
+            "text": [
+                {
+                    "text": "    let layout = alloc::Layout::from_size_align_unchecked(size, align);",
+                    "highlight_start": 65,
+                    "highlight_end": 70
+                }
+            ],
+            "label": "expected usize, found u32",
+            "suggested_replacement": null,
+            "suggestion_applicability": null,
+            "expansion": null
+        }
+    ],
+    "children": [],
+    "rendered": "error[E0308]: mismatched types\n  --> runtime/compiler_support.rs:48:65\n   |\n48 |     let layout = alloc::Layout::from_size_align_unchecked(size, align);\n   |                                                                 ^^^^^ expected usize, found u32\n\n"
+}
diff --git a/editors/code/src/test/utils/diagnotics/rust.test.ts b/editors/code/src/test/utils/diagnotics/rust.test.ts
index b555a4819..7fb003fe2 100644
--- a/editors/code/src/test/utils/diagnotics/rust.test.ts
+++ b/editors/code/src/test/utils/diagnotics/rust.test.ts
@@ -108,7 +108,10 @@ describe('mapRustDiagnosticToVsCode', () => {
         );
         assert.strictEqual(
             diagnostic.message,
-            'this function takes 2 parameters but 3 parameters were supplied'
+            [
+                'this function takes 2 parameters but 3 parameters were supplied',
+                'expected 2 parameters'
+            ].join('\n')
         );
         assert.strictEqual(diagnostic.code, 'E0061');
         assert.strictEqual(diagnostic.source, 'rustc');
@@ -170,4 +173,28 @@ describe('mapRustDiagnosticToVsCode', () => {
             SuggestionApplicability.Unspecified
         );
     });
+
+    it('should map a mismatched type error', () => {
+        const { diagnostic, suggestedFixes } = mapFixtureToVsCode(
+            'error/E0308'
+        );
+
+        assert.strictEqual(
+            diagnostic.severity,
+            vscode.DiagnosticSeverity.Error
+        );
+        assert.strictEqual(
+            diagnostic.message,
+            ['mismatched types', 'expected usize, found u32'].join('\n')
+        );
+        assert.strictEqual(diagnostic.code, 'E0308');
+        assert.strictEqual(diagnostic.source, 'rustc');
+        assert.strictEqual(diagnostic.tags, undefined);
+
+        // No related information
+        assert.deepStrictEqual(diagnostic.relatedInformation, []);
+
+        // There are no suggested fixes
+        assert.strictEqual(suggestedFixes.length, 0);
+    });
 });
diff --git a/editors/code/src/utils/diagnostics/rust.ts b/editors/code/src/utils/diagnostics/rust.ts
index d16576eb1..c07be4559 100644
--- a/editors/code/src/utils/diagnostics/rust.ts
+++ b/editors/code/src/utils/diagnostics/rust.ts
@@ -182,6 +182,7 @@ export function mapRustDiagnosticToVsCode(
     const secondarySpans = rd.spans.filter(s => !s.is_primary);
 
     const severity = mapLevelToSeverity(rd.level);
+    let primarySpanLabel = primarySpan.label;
 
     const vd = new vscode.Diagnostic(location.range, rd.message, severity);
 
@@ -220,9 +221,17 @@ export function mapRustDiagnosticToVsCode(
         }
         if (messageLine) {
             vd.message += `\n${messageLine}`;
+
+            // These secondary messages usually duplicate the content of the
+            // primary span label.
+            primarySpanLabel = undefined;
         }
     }
 
+    if (primarySpanLabel) {
+        vd.message += `\n${primarySpanLabel}`;
+    }
+
     if (isUnusedOrUnnecessary(rd)) {
         vd.tags = [vscode.DiagnosticTag.Unnecessary];
     }