Match prefix patterns for dependencies

[felix]

Reasonably naive but stops a lot of false warnings for me.

[owenrumney]

Thanks for this — the approach is right, but the prefix-only match suppresses more than intended: strings.Cut discards the suffix, so a pattern like %.o has prefix "" and strings.HasPrefix(s, "") matches every dep — one %.o: %.c rule in a Makefile turns off all undefined-target warnings. Same for suffixed patterns like out/%.exe vs a dep out/foo.

Checking both halves fixes it while keeping your src/% case working:

prefix, suffix, hasPattern := strings.Cut(t.Name, "%")
if hasPattern && len(s) > len(prefix)+len(suffix) &&
	strings.HasPrefix(s, prefix) && strings.HasSuffix(s, suffix) {

The length guard mirrors make's rule that % matches at least one character.

Verified locally: with that change, TestDiagnoseFindsPatternDeps still passes, and this regression case goes green:

func TestPatternRuleDoesNotSuppressUnrelatedWarnings(t *testing.T) {
	input := `all: nonexistent
	echo hi

%.o: %.c
	$(CC) -c $< -o $@
`
	mf := parser.Parse(testURI, input)
	diags := Diagnose(mf)

	var found bool
	for _, d := range diags {
		if d.Message == "undefined target: nonexistent" {
			found = true
		}
	}
	assert.True(t, found)
}

Happy to merge with those two changes.

[owenrumney]

thanks @felix - appreciate the contribution, releasing now.