feat(raycicmd): add matrix expansion types and selector resolution

Rayci will expand matrix into individual Buildkite steps, allowing for fine-grained depends_on targeting of specific matrix combinations.

## Matrix Formats Supported

Simple array (anonymous dimension):
  matrix: ["3.10", "3.11", "3.12"]

Named dimensions:
  matrix:
    setup:
      python: ["3.10", "3.11"]
      cuda: ["12.1.1", "12.8.1"]

## Key Generation

Expanded keys follow deterministic format:
  {base-key}-{dim1}{val1}-{dim2}{val2}

Examples:
  ray-build + python=3.11, cuda=12.1.1 → ray-build-cuda1211-python311
  ray-build + ["linux", "darwin"]      → ray-build-linux, ray-build-darwin

## Selector Syntax for depends_on

Simple reference (waits for ALL instances via meta-step):
  depends_on: ray-build

Selector syntax (waits for matching instances only):
  depends_on:
    - key: ray-build
      matrix:
        cuda: "12.1.1"           # matches all python versions with cuda 12.1.1

Multi-value selector:
  depends_on:
    - key: ray-build
      matrix:
        python: ["3.10", "3.11"]  # matches specific python versions

Topic: matrix-expand
Signed-off-by: andrew <andrew@anyscale.com>

Author: andrew-anyscale

raycicmd/matrix_expand.go

@@ -0,0 +1,370 @@
+package raycicmd
+
+import (
+	"fmt"
+	"maps"
+	"slices"
+	"sort"
+	"strings"
+)
+
+// dimension is a named dimension in a matrix (e.g., "python", "cuda").
+type dimension string
+
+// anonymousDim is used for simple array matrices: matrix: ["a", "b", "c"]
+const anonymousDim dimension = ""
+
+// variant is a value within a dimension (e.g., "3.10", "12.1.1").
+type variant string
+
+// matrixConfig represents an expanded step's matrix definition.
+type matrixConfig struct {
+	Setup map[dimension][]variant
+}
+
+// matrixInstance represents a single expanded matrix combination.
+type matrixInstance struct {
+	Values map[dimension]variant
+}
+
+// matrixSelector represents a dependency selector with optional matrix filter.
+type matrixSelector struct {
+	Key    string                  // base step key
+	Matrix map[dimension][]variant // partial dimension constraints (nil = all), each dimension can match multiple values
+}
+
+// parseMatrixConfig parses the matrix field from a step.
+// Named dimensions matrix
+//
+//	matrix:
+//	  setup:
+//	    python: ["3.10", "3.11"]
+//	    cuda: ["12.1.1", "12.8.1"]
+//
+// Simple array matrix (no dimension name)
+//
+//	matrix:
+//	  - "darwin"
+//	  - "Linux"
+//	  - "Windows"
+func parseMatrixConfig(v any) (*matrixConfig, error) {
+	cfg := &matrixConfig{
+		Setup: make(map[dimension][]variant),
+	}
+
+	switch val := v.(type) {
+	case []any:
+		// Simple array: matrix: ["3.10", "3.11"]
+		variants, err := anySliceToVariantSlice(val)
+		if err != nil {
+			return nil, fmt.Errorf("invalid matrix array: %w", err)
+		}
+		cfg.Setup[anonymousDim] = variants
+
+	case map[string]any:
+		// Map with setup and optional adjustments
+		if setup, ok := val["setup"]; ok {
+			setupMap, ok := setup.(map[string]any)
+			if !ok {
+				return nil, fmt.Errorf("matrix.setup must be a map")
+			}
+			for dim, vals := range setupMap {
+				valsSlice, ok := vals.([]any)
+				if !ok {
+					return nil, fmt.Errorf("matrix.setup.%s must be an array", dim)
+				}
+				variants, err := anySliceToVariantSlice(valsSlice)
+				if err != nil {
+					return nil, fmt.Errorf("invalid values for dimension %s: %w", dim, err)
+				}
+				cfg.Setup[dimension(dim)] = variants
+			}
+		} else {
+			return nil, fmt.Errorf("matrix map must have 'setup' key")
+		}
+
+		if _, ok := val["adjustments"]; ok {
+			return nil, fmt.Errorf("matrix.adjustments is not supported")
+		}
+
+	default:
+		return nil, fmt.Errorf("matrix must be an array or map, got %T", v)
+	}
+
+	return cfg, nil
+}
+
+func (cfg *matrixConfig) sortedDimensions() []dimension {
+	dims := make([]dimension, 0, len(cfg.Setup))
+	for dim := range cfg.Setup {
+		dims = append(dims, dim)
+	}
+	sort.Slice(dims, func(i, j int) bool { return dims[i] < dims[j] })
+	return dims
+}
+
+// expand generates all combinations from a matrix config.
+func (cfg *matrixConfig) expand() []*matrixInstance {
+	if len(cfg.Setup) == 0 {
+		return nil
+	}
+
+	result := []*matrixInstance{{Values: make(map[dimension]variant)}}
+	for _, dim := range cfg.sortedDimensions() {
+		var expanded []*matrixInstance
+		for _, inst := range result {
+			for _, val := range cfg.Setup[dim] {
+				newInst := &matrixInstance{Values: maps.Clone(inst.Values)}
+				newInst.Values[dim] = val
+				expanded = append(expanded, newInst)
+			}
+		}
+		result = expanded
+	}
+	return result
+}
+
+// generateKey creates the expanded key for an instance.
+// Format: {base-key}-{dim1}{val1}-{dim2}{val2} (dims sorted alphabetically)
+func (inst *matrixInstance) generateKey(baseKey string, cfg *matrixConfig) string {
+	parts := []string{baseKey}
+	for _, dim := range cfg.sortedDimensions() {
+		parts = append(parts, sanitizeKeyPart(string(dim)+string(inst.Values[dim])))
+	}
+	return strings.Join(parts, "-")
+}
+
+// sanitizeKeyPart removes invalid characters from a key part.
+// Buildkite keys allow: alphanumeric, underscores, dashes, colons.
+// We exclude dashes here since they're used as separators between parts.
+func sanitizeKeyPart(s string) string {
+	return strings.Map(func(r rune) rune {
+		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') ||
+			(r >= '0' && r <= '9') || r == '_' || r == ':' {
+			return r
+		}
+		return -1 // drop character
+	}, s)
+}
+
+// generateTags creates auto-generated tags for matrix values.
+// These tags are used to tag the expanded steps and depends_on selectors.
+// Format: {dim1}-{val1}, {dim2}-{val2} (dims sorted alphabetically)
+func (inst *matrixInstance) generateTags() []string {
+	var tags []string
+	for dim, val := range inst.Values {
+		if dim == anonymousDim {
+			// Simple array: just use the value as tag (e.g., 3.10)
+			tags = append(tags, string(val))
+		} else {
+			// Named dimension: use dimension-value format (e.g., python-3.11)
+			tags = append(tags, string(dim)+"-"+string(val))
+		}
+	}
+	sort.Strings(tags)
+	return tags
+}
+
+// substituteValues replaces {{matrix.X}} placeholders in any value.
+// It recursively traverses maps and slices, returning a new structure with
+// all string values substituted. Non-string leaf values are returned as-is.
+func (inst *matrixInstance) substituteValues(v any) any {
+	switch val := v.(type) {
+	case string:
+		var replacerArgs []string
+		for dim, dimVal := range inst.Values {
+			if dim == anonymousDim {
+				// Simple array: use {{matrix}}
+				replacerArgs = append(replacerArgs, "{{matrix}}", string(dimVal))
+			} else {
+				// Named dimension: use {{matrix.dim}} (e.g., {{matrix.python}})
+				replacerArgs = append(replacerArgs, "{{matrix."+string(dim)+"}}", string(dimVal))
+			}
+		}
+		return strings.NewReplacer(replacerArgs...).Replace(val)
+
+	case map[string]any:
+		result := make(map[string]any)
+		for k, v := range val {
+			result[k] = inst.substituteValues(v)
+		}
+		return result
+
+	case []any:
+		result := make([]any, len(val))
+		for i, v := range val {
+			result[i] = inst.substituteValues(v)
+		}
+		return result
+
+	default:
+		return v
+	}
+}
+
+// parseMatrixDependsOn parses a depends_on field into a list of selectors.
+//
+// Supported YAML formats:
+//
+//	depends_on: step-key              # single string
+//	depends_on: [step-a, step-b]      # string array
+//	depends_on:                       # selector with matrix filter
+//	  - key: ray-build
+//	    matrix:
+//	      python: "3.11"
+func parseMatrixDependsOn(v any) ([]*matrixSelector, error) {
+	if v == nil {
+		return nil, nil
+	}
+
+	switch val := v.(type) {
+	case string:
+		return []*matrixSelector{{Key: val}}, nil
+
+	case []string:
+		var selectors []*matrixSelector
+		for _, key := range val {
+			selectors = append(selectors, &matrixSelector{Key: key})
+		}
+		return selectors, nil
+
+	case []any:
+		var selectors []*matrixSelector
+		for i, item := range val {
+			switch itemVal := item.(type) {
+			case string:
+				selectors = append(selectors, &matrixSelector{Key: itemVal})
+
+			case map[string]any:
+				sel, err := parseMatrixSelectorMap(itemVal)
+				if err != nil {
+					return nil, fmt.Errorf("depends_on[%d]: %w", i, err)
+				}
+				selectors = append(selectors, sel)
+
+			default:
+				return nil, fmt.Errorf("depends_on[%d]: unexpected type %T", i, item)
+			}
+		}
+		return selectors, nil
+
+	default:
+		return nil, fmt.Errorf("depends_on must be string or array, got %T", v)
+	}
+}
+
+// parseMatrixSelectorMap parses a selector map into a matrixSelector.
+//
+// Example YAML:
+//
+//	key: ray-build
+//	matrix:
+//	  python: ["3.10", "3.11"]
+//	  cuda: "12.1.1"
+func parseMatrixSelectorMap(m map[string]any) (*matrixSelector, error) {
+	sel := &matrixSelector{}
+
+	key, ok := m["key"]
+	if !ok {
+		return nil, fmt.Errorf("selector missing 'key' field")
+	}
+	keyStr, ok := key.(string)
+	if !ok {
+		return nil, fmt.Errorf("selector 'key' must be a string")
+	}
+	sel.Key = keyStr
+
+	if matrix, ok := m["matrix"]; ok {
+		matrixMap, ok := matrix.(map[string]any)
+		if !ok {
+			return nil, fmt.Errorf("selector 'matrix' must be a map")
+		}
+		sel.Matrix = make(map[dimension][]variant)
+		for k, v := range matrixMap {
+			dim := dimension(k)
+			switch val := v.(type) {
+			case string:
+				sel.Matrix[dim] = []variant{variant(val)}
+			case []any:
+				variants, err := anySliceToVariantSlice(val)
+				if err != nil {
+					return nil, fmt.Errorf("selector 'matrix.%s': %w", k, err)
+				}
+				sel.Matrix[dim] = variants
+			case []string:
+				variants := make([]variant, len(val))
+				for i, s := range val {
+					variants[i] = variant(s)
+				}
+				sel.Matrix[dim] = variants
+			default:
+				return nil, fmt.Errorf("selector 'matrix.%s' must be a string or array", k)
+			}
+		}
+	}
+
+	return sel, nil
+}
+
+// expand returns the expanded step keys that match this selector.
+//
+// For example, if ray-build expanded to [ray-build-python310, ray-build-python311]
+// and the selector filters to python: "3.11", this returns [ray-build-python311].
+func (sel *matrixSelector) expand(stepKeyToConfig map[string]*matrixConfig) ([]string, error) {
+	cfg, ok := stepKeyToConfig[sel.Key]
+	if !ok {
+		return []string{sel.Key}, nil
+	}
+
+	if sel.Matrix == nil {
+		return []string{sel.Key}, nil
+	}
+
+	for dim := range sel.Matrix {
+		if _, ok := cfg.Setup[dim]; !ok {
+			return nil, fmt.Errorf("selector dimension %q not found in matrix for %q", dim, sel.Key)
+		}
+	}
+
+	instances := cfg.expand()
+
+	var matches []string
+	for _, inst := range instances {
+		if inst.matches(sel) {
+			matches = append(matches, inst.generateKey(sel.Key, cfg))
+		}
+	}
+
+	if len(matches) == 0 {
+		return nil, fmt.Errorf("no matches for selector {key: %q, matrix: %v}", sel.Key, sel.Matrix)
+	}
+
+	return matches, nil
+}
+
+func (inst *matrixInstance) matches(sel *matrixSelector) bool {
+	for dim, allowedVals := range sel.Matrix {
+		if !slices.Contains(allowedVals, inst.Values[dim]) {
+			return false
+		}
+	}
+	return true
+}
+
+// hasMatrixPlaceholder checks if a string contains any {{matrix...}} placeholder.
+func hasMatrixPlaceholder(s string) bool {
+	return strings.Contains(s, "{{matrix")
+}
+
+// anySliceToVariantSlice converts []any to []variant.
+func anySliceToVariantSlice(arr []any) ([]variant, error) {
+	result := make([]variant, len(arr))
+	for i, v := range arr {
+		s, ok := v.(string)
+		if !ok {
+			return nil, fmt.Errorf("element %d is not a string: %T", i, v)
+		}
+		result[i] = variant(s)
+	}
+	return result, nil
+}