test/goroot: match missing-comma recovery diagnostics

[cpunion]

Summary

• pair the gc-style missing-comma primary with the exact duplicate emitted by go/parser
• keep matching scoped to the same canonical source, line, and exact secondary text
• enable fixedbugs/issue14520.go and syntax/composite.go in Go 1.26 errorcheck coverage

Correctness

The secondary is discarded only after the expected primary matched. A secondary by itself, a near-match, a different source/line, or an extra duplicate remains an error.

Validation

• targeted harness unit tests on Go 1.24.11, 1.25.0, and 1.26.0
• both GOROOT cases on Go 1.24.11, 1.25.0, 1.26.0, and 1.26.5
• original 149 compile/errorcheck xfail cases on Go 1.26.0: 2 pass and the remaining 147 stay expected failures
• go test ./test/goroot

Scope and overlap

No functional dependency on another PR. This does not touch interface/assertinline.go, which is handled by #2201, and does not include wasm or DWARF changes.

The Ubuntu Go workflow currently needs #2215 to install libslirp.so.0 for ESP QEMU verification. This PR does not duplicate that CI fix.

The seven compile xfails remain intentionally unchanged: their checkptr, libfuzzer, softfloat, and dynlink flags carry compiler semantics and should not be accepted as no-ops.

[fennoai]

Review: test/goroot: match missing-comma recovery diagnostics

Reviewed the diff across code quality, performance, security, and documentation accuracy.

Clean, well-scoped change. The two new parserRecoverySecondaries cases (composite literal, parameter list) follow the existing pairing convention exactly: a secondary is discarded only after its gc-style primary matched on the same file+line with exact secondary text, and parserRecoveryPair.consumed ensures only one duplicate is dropped. The comment reword (dropping "the five") is a correct fix now that the switch handles more spellings. No performance, security, or documentation-accuracy concerns.

Two minor test-quality notes are inline. Neither is a correctness bug — the harness pairing logic is exercised correctly and the PR reports validation of both enabled cases across Go 1.24.11 / 1.25.0 / 1.26.0 / 1.26.5.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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