test(#2163): fast-check property tests for the porcelain-v2 parser

Claude-Session: https://claude.ai/code/session_01Hme55Pvq6BhpgwBcyC5HAg

tests/gsd-statusline-git.property.test.cjs

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+'use strict';
+
+/**
+ * Property-based tests for the statusline git-segment parser (#2163)
+ *
+ * Module: hooks/gsd-statusline.js
+ * Exported: parseGitStatus(text), buildGitSegment(info)
+ *
+ * Properties tested:
+ *   (a) parseGitStatus: never throws on any input; returns null or the full
+ *       typed shape with non-negative counts (total robustness)
+ *   (b) round-trip: synthetic porcelain-v2 output for a generated repo state
+ *       parses back to exactly that state
+ *   (c) prefix-robustness: unknown-prefix lines (future porcelain extensions)
+ *       inserted anywhere leave the parsed result unchanged
+ *   (d) no-branch-header: any input lacking '# branch.head' parses to null
+ *   (e) buildGitSegment: never throws; '' iff branch absent; ✓ iff clean+synced
+ */
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fc = require('./helpers/fast-check-setup.cjs');
+
+const { parseGitStatus, buildGitSegment } = require('../hooks/gsd-statusline.js');
+
+const INFO_KEYS = ['branch', 'ahead', 'behind', 'staged', 'unstaged', 'untracked'];
+const COUNT_KEYS = ['ahead', 'behind', 'staged', 'unstaged', 'untracked'];
+
+// Branch names from a path-safe alphabet (no whitespace/control chars, which
+// git itself forbids in ref names).
+const arbBranch = fc.stringMatching(/^[a-zA-Z0-9][a-zA-Z0-9._/-]{0,40}$/);
+
+// A generated repo state with bounded counts.
+const arbState = fc.record({
+  branch: arbBranch,
+  ahead: fc.nat({ max: 99 }),
+  behind: fc.nat({ max: 99 }),
+  staged: fc.nat({ max: 20 }),
+  unstagedChanged: fc.nat({ max: 20 }),
+  unmerged: fc.nat({ max: 5 }),
+  untracked: fc.nat({ max: 20 }),
+});
+
+/**
+ * Render synthetic porcelain v2 --branch output for a generated state.
+ * Staged entries get XY 'M.', unstaged 'M' entries '.M', unmerged 'u UU'.
+ */
+function renderPorcelain(s) {
+  const lines = [
+    '# branch.oid 0123456789abcdef0123456789abcdef01234567',
+    `# branch.head ${s.branch}`,
+    `# branch.upstream origin/${s.branch}`,
+    `# branch.ab +${s.ahead} -${s.behind}`,
+  ];
+  for (let i = 0; i < s.staged; i++) {
+    lines.push(`1 M. N... 100644 100644 100644 0123456 0123456 staged-${i}.txt`);
+  }
+  for (let i = 0; i < s.unstagedChanged; i++) {
+    lines.push(`1 .M N... 100644 100644 100644 0123456 0123456 unstaged-${i}.txt`);
+  }
+  for (let i = 0; i < s.unmerged; i++) {
+    lines.push(`u UU N... 100644 100644 100644 100644 0123456 0123456 0123456 conflict-${i}.txt`);
+  }
+  for (let i = 0; i < s.untracked; i++) {
+    lines.push(`? new-${i}.txt`);
+  }
+  return lines.join('\n') + '\n';
+}
+
+describe('gsd-statusline git segment: parseGitStatus properties', () => {
+  // (a) Total: never throws, result is null or the full typed shape
+  test('property: never throws and returns null or a well-formed info object', () => {
+    fc.assert(
+      fc.property(
+        fc.oneof(
+          fc.constant(null),
+          fc.constant(undefined),
+          fc.constant(42),
+          fc.constant({}),
+          fc.string({ unit: 'binary', maxLength: 300 }),
+          fc.string({ unit: 'grapheme-composite', maxLength: 300 }),
+          // line soup: random lines joined with \n
+          fc.array(fc.string({ maxLength: 60 }), { maxLength: 30 }).map((a) => a.join('\n'))
+        ),
+        (input) => {
+          let result;
+          assert.doesNotThrow(() => { result = parseGitStatus(input); });
+          if (result !== null) {
+            assert.deepEqual(Object.keys(result).sort(), [...INFO_KEYS].sort());
+            for (const k of COUNT_KEYS) {
+              assert.equal(typeof result[k], 'number');
+              assert.ok(result[k] >= 0, `${k} must be >= 0`);
+            }
+            assert.equal(typeof result.branch, 'string');
+            assert.ok(result.branch.length > 0);
+          }
+        }
+      )
+    );
+  });
+
+  // (b) Round-trip: synthetic porcelain for a state parses back exactly
+  test('property: round-trip through synthetic porcelain v2 output', () => {
+    fc.assert(
+      fc.property(arbState, (s) => {
+        const parsed = parseGitStatus(renderPorcelain(s));
+        assert.ok(parsed, 'well-formed porcelain must parse');
+        assert.equal(parsed.branch, s.branch);
+        assert.equal(parsed.ahead, s.ahead);
+        assert.equal(parsed.behind, s.behind);
+        assert.equal(parsed.staged, s.staged);
+        // unmerged (conflict) entries count as unstaged
+        assert.equal(parsed.unstaged, s.unstagedChanged + s.unmerged);
+        assert.equal(parsed.untracked, s.untracked);
+      })
+    );
+  });
+
+  // (c) Prefix-robustness: unknown-prefix lines never change the result
+  test('property: unknown-prefix lines inserted anywhere are ignored', () => {
+    // Lines whose first two chars are none of the recognized prefixes
+    // ('# ', '1 ', '2 ', 'u ', '? ').
+    const arbUnknownLine = fc
+      .string({ maxLength: 50 })
+      .map((s) => `z ${s}`);
+    fc.assert(
+      fc.property(
+        arbState,
+        fc.array(arbUnknownLine, { minLength: 1, maxLength: 10 }),
+        fc.nat({ max: 1000 }),
+        (s, extras, seedPos) => {
+          const baseline = parseGitStatus(renderPorcelain(s));
+          const lines = renderPorcelain(s).split('\n');
+          // deterministic insertion positions derived from seedPos
+          extras.forEach((extra, i) => {
+            const pos = (seedPos + i * 7) % (lines.length + 1);
+            lines.splice(pos, 0, extra);
+          });
+          const withExtras = parseGitStatus(lines.join('\n'));
+          assert.deepEqual(withExtras, baseline);
+        }
+      )
+    );
+  });
+
+  // (d) No-branch-header: input without '# branch.head' parses to null
+  test('property: input lacking a branch.head header parses to null', () => {
+    fc.assert(
+      fc.property(
+        fc.array(fc.string({ maxLength: 60 }), { maxLength: 30 }),
+        (rawLines) => {
+          const text = rawLines
+            .filter((l) => !l.startsWith('# branch.head '))
+            .join('\n');
+          assert.equal(parseGitStatus(text), null);
+        }
+      )
+    );
+  });
+});
+
+describe('gsd-statusline git segment: buildGitSegment properties', () => {
+  // (e) Never throws; '' iff no branch; clean+synced renders the ✓ marker
+  test('property: never throws and is empty exactly when branch is absent', () => {
+    fc.assert(
+      fc.property(
+        fc.oneof(
+          fc.constant(null),
+          fc.constant(undefined),
+          fc.constant({}),
+          arbState.map((s) => ({
+            branch: s.branch,
+            ahead: s.ahead,
+            behind: s.behind,
+            staged: s.staged,
+            unstaged: s.unstagedChanged + s.unmerged,
+            untracked: s.untracked,
+          }))
+        ),
+        (info) => {
+          let seg;
+          assert.doesNotThrow(() => { seg = buildGitSegment(info); });
+          assert.equal(typeof seg, 'string');
+          if (!info || !info.branch) {
+            assert.equal(seg, '');
+          } else {
+            assert.ok(seg.includes(info.branch));
+            const dirty =
+              info.staged || info.unstaged || info.untracked || info.ahead || info.behind;
+            assert.equal(seg.includes('✓'), !dirty);
+          }
+        }
+      )
+    );
+  });
+});