test(lint-once): follow a short file flag with its value attached

`docker build -fDockerfile.lint .` is a plain `-f` naming a literal file —
the flag parser reads the attached value for any shorthand — but the
resolver's `[=\s]+` required a separator, so the invocation fell through to
the default `Dockerfile` edge. Mutating the `check` recipe to that spelling
left the suite 52/52 green while `-f Dockerfile.lint` was caught.

The header already promised this form was followed: it claimed the file
named by `-f` is resolved wherever the flag sits, and disclosed only a
bundled short cluster (`-qf <file>`) as unfollowed. Overclaiming is the
defect, so the resolver is taught the form rather than the claim narrowed.

The attached form is allowed only for the short flag, keeping `--force-rm`
out of it; `--file` still requires `=` or whitespace. The `-qf` cluster
limitation is untouched and still pinned.

test/packaging/lint-once.test.ts

@@ -39,11 +39,12 @@
 // one pass over literals, so a value that itself names another variable, a
 // value built by a make function (`$(shell ...)`, `$(addprefix ...)`), and the
 // body of a `define`/`endef` block are not expanded and not followed. A
-// `docker build` resolves to the file named by `-f`, `-f=`, `--file` or
-// `--file=`, wherever in the invocation that flag sits, and to `Dockerfile`
-// when it names none; a Dockerfile chosen some other way — a bundled short
-// flag cluster (`-qf <file>`), a value this walk cannot expand to a literal —
-// resolves to the default rather than to the real file. Within those edges, a
+// `docker build` resolves to the file named by `-f`, `-f=`, `-f<file>` with
+// the value attached to the flag, `--file` or `--file=`, wherever in the
+// invocation that flag sits, and to `Dockerfile` when it names none; a
+// Dockerfile chosen some other way — a bundled short flag cluster
+// (`-qf <file>`), a value this walk cannot expand to a literal — resolves to
+// the default rather than to the real file. Within those edges, a
 // prettier call is caught wherever it is added.
 //
 // Two entrypoints are walked, because they cover different graphs: `make check`
@@ -437,16 +438,19 @@ const edgesOf = (line: string): string[] => {
     // it the count would miss the one invocation that is supposed to survive.
     //
     // Every spelling of the file flag is read, not just `-f <file>`. Docker
-    // accepts `--file <file>`, `--file=<file>` and `-f=<file>` for the same
-    // thing, and matching `-f ` alone resolved all of them to the default
+    // accepts `--file <file>`, `--file=<file>`, `-f=<file>` and the value
+    // attached to the short flag as one token (`-f<file>`) for the same thing,
+    // and matching `-f ` alone resolved all of them to the default
     // `Dockerfile` edge — so `docker build --file=Dockerfile.lint .` in a
     // recipe was followed into the wrong file, counted nothing, and reported
     // green. The flag is searched for anywhere in the invocation, as `-f`
     // already was, because a real build line wraps it in `--build-arg` and
     // other flags. A leading `\s` is required so that a longer flag ending in
-    // the same letters cannot supply the match.
+    // the same letters cannot supply the match, and the attached form is
+    // allowed only for the short flag, so that `--force-rm` — a long flag that
+    // merely starts with the same letters — still does not read as one.
     if (/\bdocker\s+build\b/.test(line)) {
-        const file = /\s(?:-f|--file)[=\s]+(\S+)/.exec(line);
+        const file = /\s(?:--file[=\s]+|-f=?\s*)(\S+)/.exec(line);
         edges.push(`docker:${file === null ? "Dockerfile" : file[1]}`);
     }
 
@@ -1021,6 +1025,21 @@ describe("the resolver reads what the shell would run", () => {
         ]);
     });
 
+    // The value may be attached to the short flag with no separator at all:
+    // `-fDockerfile.lint` is a single token, and the flag parser reads it as
+    // `-f` naming that file, exactly as `-f Dockerfile.lint` does. Requiring a
+    // separator sent it to the default `Dockerfile` edge instead — the same
+    // false green as the long spellings above, and one the header promised was
+    // followed: a second prettier pass added as `docker build
+    // -fDockerfile.lint .` was resolved into the wrong file, counted nothing,
+    // and left the build green. `-fFILE` is an ordinary thing for a human to
+    // write, so it is followed rather than merely documented as unfollowed.
+    it("follows a short file flag with its value attached", () => {
+        expect(edgesOf("docker build -fDockerfile.lint .")).toEqual([
+            "docker:Dockerfile.lint",
+        ]);
+    });
+
     // The flag is found anywhere in the invocation rather than at a fixed
     // position, matching how `-f` was already read, since a real build line
     // carries `--build-arg` and friends around it.