[zac]

Summary

This PR fixes two long-standing bugs in how PathTemplate builds request paths:

1. Values were percent-encoded twice. a b went out as a%2520b.
2. includesSlash: false deleted slashes written in the template. "testing/\(path: \.name, includesSlash: false).test" built testingfirst.test.

1. Encode path values exactly once

The bug had been there since the first commit. String.pathSafe encoded each value, then urlRequest(in:) assigned the joined path to URLComponents.path, which encodes again. In 2019, 5077dd2 ("Possible fix for double-encoding issues") fixed the same problem for query and form values, but the path side was missed, because every path test used plain values. I found no issue, PR, or test that relied on the double encoding.

• String.pathSafe encodes a value as one segment, including /, ?, and #. It keeps . and .. as encoded segments so URL resolution doesn't collapse them.
• Every component goes through a normalizer, and the result is assigned to percentEncodedPath. The normalizer keeps valid %XX escapes and encodes anything else not allowed in a path. Custom PathRepresentable values that return raw text are now encoded instead of trapping.
• Literal template text keeps its slashes and honours %XX escapes. Form body encoding is byte-identical to before.

2. Keep literal slashes next to embedded values

This was the failing test added on feature/path-slash-fix in January 2021, which never got a fix. includesSlash: false removed whatever slash came before the value. It now removes only a slash the template inserted automatically.

Default interpolations are unchanged: each value is its own path segment, so "files/\(path: \.id).json" still builds files/42/.json. Embedding a value uses includesSlash: false, giving files/42.json. The PathTemplate docs and Examples.md now state the rule. No existing test expectation changed.

Behaviour changes to review

• A / inside a String value is now sent as %2F. Before, "folder/file.txt" became two segments. This is the one change someone might have relied on deliberately. It matches RFC 3986 and OpenAPI, and it stops values from adding path structure. To insert a value that spans several segments, conform a type to PathRepresentable and return its separators unencoded.
• Pass raw values. A pre-encoded a%20b is now sent as a%2520b (a literal %20).
• Templates that combine literal / with includesSlash: false now keep that slash. They previously lost it.

Testing

• Encoding: new tests assert both url.absoluteString and percentEncodedPath for:
  • a space, %, Unicode, embedded / and //, ?, #, . and .., and a pre-encoded value
  • custom conformers returning raw text, valid escapes, invalid escapes, and incomplete escapes
  • a value adjacent to literal text, optional values, and literal template encoding
• Slashes: new tests cover:
  • the two 2021 cases
  • an embedded files/{id}.json
  • two embedded values in one segment
  • the default files/42/.json, pinned
  • nil optionals at the start, middle, and end
• All of these failed before the fixes.
• macOS (Swift 6.4): 103 tests pass.
• Linux (swift:6.0 in Docker): 55 tests pass. Linux runs fewer suites because EndpointsMocking is Apple-only.

Coverage (line, macOS)

PathTemplate.swift 98.3%, Endpoint+URLRequest.swift 97.0%, Array+Form.swift 85.7%. Endpoints overall is 74.9%; the low-coverage files aren't touched by this PR.