fix(compilers/openapi): warn on a duplicate server name

compilers/openapi/internal/diag/diag.go

@@ -165,6 +165,17 @@ const (
 	//
 	// Error, as the parser's report was.
 	DuplicateParameter = "openapi/duplicate-parameter"
+	// DuplicateServerName reports a servers list entry whose name an earlier
+	// entry in the same list already has, compared as written, at the repeat's
+	// name. Load checks every list the source writes, the document's, a path
+	// item's or an operation's, lowered or not, but none only a $ref reaches
+	// (GitHub #880). Both entries are kept, though a consumer keying servers by
+	// name cannot tell them apart. Names equal once canonicalized, and URL
+	// hints, are not reported: an emitter uniquifies them.
+	//
+	// Warning, where DuplicateParameter is an error: OpenAPI 3.2 calls the name
+	// "an optional unique string" with no RFC 2119 keyword.
+	DuplicateServerName = "openapi/duplicate-server-name"
 	// InvalidMethodKey reports an additionalOperations key that names no method:
 	// the empty string. The operation still lowers, binding the key as written, so
 	// nothing the entry declares is lost — what is reported is that the binding's

compilers/openapi/internal/diag/diag_test.go

@@ -138,7 +138,7 @@ func codes() []string {
 		diag.OverlayAction, diag.OverlayOriginIncomplete,
 		diag.ValidationOnlyKeyword, diag.FalseSchema, diag.EmptyEnum, diag.DuplicateEnumValue,
 		diag.NumericPrecision, diag.ExclusiveBoundForm, diag.InvalidStatusKey,
-		diag.DuplicateStatusKey, diag.DuplicateParameter,
+		diag.DuplicateStatusKey, diag.DuplicateParameter, diag.DuplicateServerName,
 		diag.InvalidMethodKey, diag.DegradedConstruct,
 		diag.CompositionLowering, diag.DynamicRefExpanded, diag.ConflictingRedecl,
 		diag.DisjointVisibility,

compilers/openapi/internal/load/later_internal_test.go

@@ -360,7 +360,7 @@ components:
 }
 
 // TestLaterConstructs_AWalkThatPanicsIsReported pins the barrier around the
-// walk, as parameterRepeats has one: a panic is an error at the model reached.
+// walk, as listRepeats has one: a panic is an error at the model reached.
 func TestLaterConstructs_AWalkThatPanicsIsReported(t *testing.T) {
 	t.Parallel()
 	panics := func(func(soa.WalkItem) bool) { panic("walk fault") }

compilers/openapi/internal/load/load.go

@@ -308,13 +308,13 @@ func validated(ctx context.Context, at func(jsontext.Pointer) ir.Provenance, loc
 }
 
 // sourceChecks runs the rules the compiler checks over the resolved source:
-// the repeats of a parameter list, and the references refused for reading past
-// a path item $ref into the fields beside it, less any resolved already
-// reports (see besideRefs).
+// the repeats of a parameter or servers list, and the references refused for
+// reading past a path item $ref into the fields beside it, less any resolved
+// already reports (see besideRefs).
 func sourceChecks(ctx context.Context, at func(jsontext.Pointer) ir.Provenance, doc *soa.OpenAPI, sibs Siblings,
 	resolved []ir.Diagnostic,
 ) []ir.Diagnostic {
-	diags := parameterRepeats(at, sibs, walkSource(ctx, doc, sibs))
+	diags := listRepeats(at, sibs, walkSource(ctx, doc, sibs))
 	return append(diags, besideRefs(at, sibs, walkSource(ctx, doc, sibs), resolved)...)
 }
 
@@ -357,8 +357,8 @@ func dropped(verr validation.Error) bool {
 //
 // Parameter uniqueness: the library reads only inline entries, so a repeat
 // through a $ref went unreported, and beside the compiler's own report an
-// inline repeat drew two errors. parameterRepeats checks every list the source
-// writes, its $refs resolved (#634, #840).
+// inline repeat drew two errors. listRepeats checks every parameter list the
+// source writes, its $refs resolved (#634, #840).
 func compilerOwned(verr validation.Error) bool {
 	return verr.Rule == validation.RuleValidationOperationIdUnique ||
 		verr.Rule == validation.RuleValidationOperationParameters

compilers/openapi/internal/load/load_internal_test.go

@@ -111,7 +111,7 @@ paths:
 
 // TestLoad_ParameterUniquenessIsTheCompilers pins compilerOwned's second
 // member: the library's report of an inline repeat is dropped, and the
-// compiler's own (parameterRepeats) is the one report, at the repeat. As for
+// compiler's own (paramRepeats) is the one report, at the repeat. As for
 // operationIds, the test first confirms the library raises its finding for the
 // fixture, or a library that stopped would leave this passing with nothing
 // dropped.