Fix `cargo watch` code action filtering

There are two issues with the implementation of `provideCodeActions`
introduced in #1439:

1. We're returning the code action based on the file its diagnostic is
   in; not the file the suggested fix is in. I'm not sure how often
   fixes are suggested cross-file but it's something we should handle.

2. We're not filtering code actions based on the passed range. The means
   if there is any suggestion in a file we'll show an action for every
   line of the file. I naively thought that VS Code would filter for us
   but that was wrong.

Unfortunately the VS Code `CodeAction` object is very complex - it can
handle edits across multiple files, run commands, etc. This makes it
complex to check them for equality or see if any of their edits
intersects with a specified range.

To make it easier to work with suggestions this introduces a
`SuggestedFix` model object and a `SuggestFixCollection` code action
provider. This is a layer between the raw Rust JSON and VS Code's
`CodeAction`s. I was reluctant to introduce another layer of abstraction
here but my attempt to work directly with VS Code's model objects was
worse.

4 files changed, 529 insertions, 0 deletions

diff --git a/editors/code/src/test/utils/diagnotics/SuggestedFix.test.ts b/editors/code/src/test/utils/diagnotics/SuggestedFix.test.ts
new file mode 100644
index 000000000..6c7f436f3
--- /dev/null
+++ b/editors/code/src/test/utils/diagnotics/SuggestedFix.test.ts
@@ -0,0 +1,133 @@
+import * as assert from 'assert';
+import * as vscode from 'vscode';
+
+import { SuggestionApplicability } from '../../../utils/diagnostics/rust';
+import SuggestedFix from '../../../utils/diagnostics/SuggestedFix';
+
+const location1 = new vscode.Location(
+    vscode.Uri.file('/file/1'),
+    new vscode.Range(new vscode.Position(1, 2), new vscode.Position(3, 4))
+);
+
+const location2 = new vscode.Location(
+    vscode.Uri.file('/file/2'),
+    new vscode.Range(new vscode.Position(5, 6), new vscode.Position(7, 8))
+);
+
+describe('SuggestedFix', () => {
+    describe('isEqual', () => {
+        it('should treat identical instances as equal', () => {
+            const suggestion1 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            const suggestion2 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            assert(suggestion1.isEqual(suggestion2));
+        });
+
+        it('should treat instances with different titles as inequal', () => {
+            const suggestion1 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            const suggestion2 = new SuggestedFix(
+                'Not the same title!',
+                location1,
+                'With this!'
+            );
+
+            assert(!suggestion1.isEqual(suggestion2));
+        });
+
+        it('should treat instances with different replacements as inequal', () => {
+            const suggestion1 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            const suggestion2 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With something else!'
+            );
+
+            assert(!suggestion1.isEqual(suggestion2));
+        });
+
+        it('should treat instances with different locations as inequal', () => {
+            const suggestion1 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            const suggestion2 = new SuggestedFix(
+                'Replace me!',
+                location2,
+                'With this!'
+            );
+
+            assert(!suggestion1.isEqual(suggestion2));
+        });
+
+        it('should treat instances with different applicability as inequal', () => {
+            const suggestion1 = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!',
+                SuggestionApplicability.MachineApplicable
+            );
+
+            const suggestion2 = new SuggestedFix(
+                'Replace me!',
+                location2,
+                'With this!',
+                SuggestionApplicability.HasPlaceholders
+            );
+
+            assert(!suggestion1.isEqual(suggestion2));
+        });
+    });
+
+    describe('toCodeAction', () => {
+        it('should map a simple suggestion', () => {
+            const suggestion = new SuggestedFix(
+                'Replace me!',
+                location1,
+                'With this!'
+            );
+
+            const codeAction = suggestion.toCodeAction();
+            assert.strictEqual(codeAction.kind, vscode.CodeActionKind.QuickFix);
+            assert.strictEqual(codeAction.title, 'Replace me!');
+            assert.strictEqual(codeAction.isPreferred, false);
+
+            const edit = codeAction.edit;
+            if (!edit) {
+                return assert.fail('Code Action edit unexpectedly missing');
+            }
+
+            const editEntries = edit.entries();
+            assert.strictEqual(editEntries.length, 1);
+
+            const [[editUri, textEdits]] = editEntries;
+            assert.strictEqual(editUri.toString(), location1.uri.toString());
+
+            assert.strictEqual(textEdits.length, 1);
+            const [textEdit] = textEdits;
+
+            assert(textEdit.range.isEqual(location1.range));
+            assert.strictEqual(textEdit.newText, 'With this!');
+        });
+    });
+});
diff --git a/editors/code/src/test/utils/diagnotics/SuggestedFixCollection.test.ts b/editors/code/src/test/utils/diagnotics/SuggestedFixCollection.test.ts
new file mode 100644
index 000000000..f0328893e
--- /dev/null
+++ b/editors/code/src/test/utils/diagnotics/SuggestedFixCollection.test.ts
@@ -0,0 +1,125 @@
+import * as assert from 'assert';
+import * as vscode from 'vscode';
+
+import SuggestedFix from '../../../utils/diagnostics/SuggestedFix';
+import SuggestedFixCollection from '../../../utils/diagnostics/SuggestedFixCollection';
+
+const uri1 = vscode.Uri.file('/file/1');
+const uri2 = vscode.Uri.file('/file/2');
+
+const mockDocument1 = ({
+    uri: uri1
+} as unknown) as vscode.TextDocument;
+
+const mockDocument2 = ({
+    uri: uri2
+} as unknown) as vscode.TextDocument;
+
+const range1 = new vscode.Range(
+    new vscode.Position(1, 2),
+    new vscode.Position(3, 4)
+);
+const range2 = new vscode.Range(
+    new vscode.Position(5, 6),
+    new vscode.Position(7, 8)
+);
+
+const diagnostic1 = new vscode.Diagnostic(range1, 'First diagnostic');
+const diagnostic2 = new vscode.Diagnostic(range2, 'Second diagnostic');
+
+// This is a mutable object so return a fresh instance every time
+function suggestion1(): SuggestedFix {
+    return new SuggestedFix(
+        'Replace me!',
+        new vscode.Location(uri1, range1),
+        'With this!'
+    );
+}
+
+describe('SuggestedFixCollection', () => {
+    it('should add a suggestion then return it as a code action', () => {
+        const suggestedFixes = new SuggestedFixCollection();
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic1);
+
+        // Specify the document and range that exactly matches
+        const codeActions = suggestedFixes.provideCodeActions(
+            mockDocument1,
+            range1
+        );
+
+        assert.strictEqual(codeActions.length, 1);
+        const [codeAction] = codeActions;
+        assert.strictEqual(codeAction.title, suggestion1().title);
+
+        const { diagnostics } = codeAction;
+        if (!diagnostics) {
+            return assert.fail('Diagnostics unexpectedly missing');
+        }
+
+        assert.strictEqual(diagnostics.length, 1);
+        assert.strictEqual(diagnostics[0], diagnostic1);
+    });
+
+    it('should not return code actions for different ranges', () => {
+        const suggestedFixes = new SuggestedFixCollection();
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic1);
+
+        const codeActions = suggestedFixes.provideCodeActions(
+            mockDocument1,
+            range2
+        );
+
+        assert(!codeActions || codeActions.length === 0);
+    });
+
+    it('should not return code actions for different documents', () => {
+        const suggestedFixes = new SuggestedFixCollection();
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic1);
+
+        const codeActions = suggestedFixes.provideCodeActions(
+            mockDocument2,
+            range1
+        );
+
+        assert(!codeActions || codeActions.length === 0);
+    });
+
+    it('should not return code actions that have been cleared', () => {
+        const suggestedFixes = new SuggestedFixCollection();
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic1);
+        suggestedFixes.clear();
+
+        const codeActions = suggestedFixes.provideCodeActions(
+            mockDocument1,
+            range1
+        );
+
+        assert(!codeActions || codeActions.length === 0);
+    });
+
+    it('should merge identical suggestions together', () => {
+        const suggestedFixes = new SuggestedFixCollection();
+
+        // Add the same suggestion for two diagnostics
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic1);
+        suggestedFixes.addSuggestedFixForDiagnostic(suggestion1(), diagnostic2);
+
+        const codeActions = suggestedFixes.provideCodeActions(
+            mockDocument1,
+            range1
+        );
+
+        assert.strictEqual(codeActions.length, 1);
+        const [codeAction] = codeActions;
+        const { diagnostics } = codeAction;
+
+        if (!diagnostics) {
+            return assert.fail('Diagnostics unexpectedly missing');
+        }
+
+        // We should be associated with both diagnostics
+        assert.strictEqual(diagnostics.length, 2);
+        assert.strictEqual(diagnostics[0], diagnostic1);
+        assert.strictEqual(diagnostics[1], diagnostic2);
+    });
+});
diff --git a/editors/code/src/test/utils/diagnotics/rust.test.ts b/editors/code/src/test/utils/diagnotics/rust.test.ts
new file mode 100644
index 000000000..b555a4819
--- /dev/null
+++ b/editors/code/src/test/utils/diagnotics/rust.test.ts
@@ -0,0 +1,173 @@
+import * as assert from 'assert';
+import * as fs from 'fs';
+import * as vscode from 'vscode';
+
+import {
+    MappedRustDiagnostic,
+    mapRustDiagnosticToVsCode,
+    RustDiagnostic,
+    SuggestionApplicability
+} from '../../../utils/diagnostics/rust';
+
+function loadDiagnosticFixture(name: string): RustDiagnostic {
+    const jsonText = fs
+        .readFileSync(
+            // We're actually in our JavaScript output directory, climb out
+            `${__dirname}/../../../../src/test/fixtures/rust-diagnostics/${name}.json`
+        )
+        .toString();
+
+    return JSON.parse(jsonText);
+}
+
+function mapFixtureToVsCode(name: string): MappedRustDiagnostic {
+    const rd = loadDiagnosticFixture(name);
+    const mapResult = mapRustDiagnosticToVsCode(rd);
+
+    if (!mapResult) {
+        return assert.fail('Mapping unexpectedly failed');
+    }
+    return mapResult;
+}
+
+describe('mapRustDiagnosticToVsCode', () => {
+    it('should map an incompatible type for trait error', () => {
+        const { diagnostic, suggestedFixes } = mapFixtureToVsCode(
+            'error/E0053'
+        );
+
+        assert.strictEqual(
+            diagnostic.severity,
+            vscode.DiagnosticSeverity.Error
+        );
+        assert.strictEqual(diagnostic.source, 'rustc');
+        assert.strictEqual(
+            diagnostic.message,
+            [
+                `method \`next\` has an incompatible type for trait`,
+                `expected type \`fn(&mut ty::list_iter::ListIterator<'list, M>) -> std::option::Option<&ty::Ref<M>>\``,
+                `   found type \`fn(&ty::list_iter::ListIterator<'list, M>) -> std::option::Option<&'list ty::Ref<M>>\``
+            ].join('\n')
+        );
+        assert.strictEqual(diagnostic.code, 'E0053');
+        assert.strictEqual(diagnostic.tags, undefined);
+
+        // No related information
+        assert.deepStrictEqual(diagnostic.relatedInformation, []);
+
+        // There are no suggested fixes
+        assert.strictEqual(suggestedFixes.length, 0);
+    });
+
+    it('should map an unused variable warning', () => {
+        const { diagnostic, suggestedFixes } = mapFixtureToVsCode(
+            'warning/unused_variables'
+        );
+
+        assert.strictEqual(
+            diagnostic.severity,
+            vscode.DiagnosticSeverity.Warning
+        );
+        assert.strictEqual(
+            diagnostic.message,
+            [
+                'unused variable: `foo`',
+                '#[warn(unused_variables)] on by default'
+            ].join('\n')
+        );
+        assert.strictEqual(diagnostic.code, 'unused_variables');
+        assert.strictEqual(diagnostic.source, 'rustc');
+        assert.deepStrictEqual(diagnostic.tags, [
+            vscode.DiagnosticTag.Unnecessary
+        ]);
+
+        // No related information
+        assert.deepStrictEqual(diagnostic.relatedInformation, []);
+
+        // One suggested fix available to prefix the variable
+        assert.strictEqual(suggestedFixes.length, 1);
+        const [suggestedFix] = suggestedFixes;
+        assert.strictEqual(
+            suggestedFix.title,
+            'consider prefixing with an underscore: `_foo`'
+        );
+        assert.strictEqual(
+            suggestedFix.applicability,
+            SuggestionApplicability.MachineApplicable
+        );
+    });
+
+    it('should map a wrong number of parameters error', () => {
+        const { diagnostic, suggestedFixes } = mapFixtureToVsCode(
+            'error/E0061'
+        );
+
+        assert.strictEqual(
+            diagnostic.severity,
+            vscode.DiagnosticSeverity.Error
+        );
+        assert.strictEqual(
+            diagnostic.message,
+            'this function takes 2 parameters but 3 parameters were supplied'
+        );
+        assert.strictEqual(diagnostic.code, 'E0061');
+        assert.strictEqual(diagnostic.source, 'rustc');
+        assert.strictEqual(diagnostic.tags, undefined);
+
+        // One related information for the original definition
+        const relatedInformation = diagnostic.relatedInformation;
+        if (!relatedInformation) {
+            return assert.fail('Related information unexpectedly undefined');
+        }
+        assert.strictEqual(relatedInformation.length, 1);
+        const [related] = relatedInformation;
+        assert.strictEqual(related.message, 'defined here');
+
+        // There are no suggested fixes
+        assert.strictEqual(suggestedFixes.length, 0);
+    });
+
+    it('should map a Clippy copy pass by ref warning', () => {
+        const { diagnostic, suggestedFixes } = mapFixtureToVsCode(
+            'clippy/trivially_copy_pass_by_ref'
+        );
+
+        assert.strictEqual(
+            diagnostic.severity,
+            vscode.DiagnosticSeverity.Warning
+        );
+        assert.strictEqual(diagnostic.source, 'clippy');
+        assert.strictEqual(
+            diagnostic.message,
+            [
+                'this argument is passed by reference, but would be more efficient if passed by value',
+                '#[warn(clippy::trivially_copy_pass_by_ref)] implied by #[warn(clippy::all)]',
+                'for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#trivially_copy_pass_by_ref'
+            ].join('\n')
+        );
+        assert.strictEqual(diagnostic.code, 'trivially_copy_pass_by_ref');
+        assert.strictEqual(diagnostic.tags, undefined);
+
+        // One related information for the lint definition
+        const relatedInformation = diagnostic.relatedInformation;
+        if (!relatedInformation) {
+            return assert.fail('Related information unexpectedly undefined');
+        }
+        assert.strictEqual(relatedInformation.length, 1);
+        const [related] = relatedInformation;
+        assert.strictEqual(related.message, 'lint level defined here');
+
+        // One suggested fix to pass by value
+        assert.strictEqual(suggestedFixes.length, 1);
+        const [suggestedFix] = suggestedFixes;
+        assert.strictEqual(
+            suggestedFix.title,
+            'consider passing by value instead: `self`'
+        );
+        // Clippy does not mark this with any applicability
+        assert.strictEqual(
+            suggestedFix.applicability,
+            SuggestionApplicability.Unspecified
+        );
+    });
+});
diff --git a/editors/code/src/test/utils/diagnotics/vscode.test.ts b/editors/code/src/test/utils/diagnotics/vscode.test.ts
new file mode 100644
index 000000000..542dec1f5
--- /dev/null
+++ b/editors/code/src/test/utils/diagnotics/vscode.test.ts
@@ -0,0 +1,98 @@
+import * as assert from 'assert';
+import * as vscode from 'vscode';
+
+import { areDiagnosticsEqual } from '../../../utils/diagnostics/vscode';
+
+const range1 = new vscode.Range(
+    new vscode.Position(1, 2),
+    new vscode.Position(3, 4)
+);
+
+const range2 = new vscode.Range(
+    new vscode.Position(5, 6),
+    new vscode.Position(7, 8)
+);
+
+describe('areDiagnosticsEqual', () => {
+    it('should treat identical diagnostics as equal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different sources as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+        diagnostic1.source = 'rustc';
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+        diagnostic2.source = 'clippy';
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different ranges as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range2,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different messages as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Goodbye!, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different severities as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Warning
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+});