clang-tidy: merge nested if()s

[vszakats]

Reported by clang-tidy 23.1.0+ via readability-redundant-nested-if.

Do not enforce at this time, due to a handful of places where it 1)
applies conditionally for non-debug builds (cf-h2-proxy.c), 2)
decreases readability (cookie.c, probably could be fixed by using temp
variables or code refactor), 3) breaks code structure (protocol.c).

Ref: https://clang.llvm.org/extra/clang-tidy/checks/readability/redundant-nested-if.html

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https://github.com/curl/curl/pull/22793/files?w=1

[Copilot]

🟢 Approval recommended

The merged conditions preserve evaluation order and short-circuit behavior across the reviewed changes.

Pull request overview

Merges redundant nested if statements throughout curl while leaving clang-tidy enforcement disabled for remaining exceptions.

Changes:

• Combines nested conditions without changing short-circuit behavior.
• Updates tests and examples consistently.
• Documents the disabled clang-tidy check.

File summaries

File	Description
tests/unit/unit2603.c	Simplifies parser assertion.
tests/unit/unit1675.c	Simplifies IPv6 zone validation.
tests/unit/unit1627.c	Simplifies scheme validation.
tests/server/socksd.c	Simplifies tunnel completion handling.
tests/libtest/lib758.c	Combines timeout conditions.
tests/libtest/lib556.c	Combines output-write conditions.
tests/libtest/lib530.c	Combines timeout conditions.
tests/libtest/lib3102.c	Simplifies certificate checks.
tests/libtest/lib1560.c	Simplifies URL-part validation.
tests/libtest/cli_h2_pausing.c	Simplifies pause-state validation.
src/var.c	Simplifies variable transformations and parsing.
src/tool_writeout.c	Simplifies write-out conditions.
src/tool_urlglob.c	Simplifies glob element handling.
src/tool_getparam.c	Simplifies option validation.
src/tool_formparse.c	Simplifies seek and escape handling.
src/tool_cb_wrt.c	Simplifies header writing.
src/tool_cb_dbg.c	Combines trace-output conditions.
src/config2setopts.c	Simplifies TLS-version adjustment.
lib/vtls/openssl.c	Simplifies PKCS#11 setup checks.
lib/urlapi.c	Simplifies IDN conversion condition.
lib/url.c	Simplifies connection matching and credential checks.
lib/telnet.c	Combines timeout checks.
lib/smtp.c	Simplifies address, MIME, and disconnect logic.
lib/select.c	Simplifies poll descriptor handling.
lib/rtsp.c	Simplifies range and transport parsing.
lib/pop3.c	Simplifies authentication and disconnect logic.
lib/multi.c	Simplifies Winsock event selection.
lib/mime.c	Simplifies MIME header decisions.
lib/imap.c	Simplifies MIME, flags, listing, and disconnect logic.
lib/http.c	Simplifies authentication, headers, and time conditions.
lib/http_aws_sigv4.c	Simplifies SigV4 buffer handling.
lib/ftp.c	Simplifies missing-file handling.
lib/formdata.c	Simplifies form validation and MIME setup.
lib/easy.c	Simplifies pause event updates.
lib/curlx/inet_pton.c	Simplifies leading IPv6 colon validation.
lib/curl_share.c	Simplifies share callbacks.
lib/cshutdn.c	Simplifies shutdown event handling.
lib/connect.c	Simplifies ALPN matching.
lib/cf-socket.c	Simplifies interface binding.
lib/cf-ip-happy.c	Simplifies reply-time selection.
lib/cf-https-connect.c	Simplifies Happy Eyeballs timing.
lib/cf-h2-proxy.c	Simplifies final-response detection.
docs/examples/websocket.c	Simplifies PONG comparison.
docs/examples/multi-double.c	Simplifies completion handling.
.clang-tidy.yml	Documents the unenforced check.

Review details

• Files reviewed: 45/45 changed files
• Comments generated: 0
• Review effort level: Balanced

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[icing]

A great way to make backports more annoying?