136 lines
4.8 KiB
Go
136 lines
4.8 KiB
Go
package convert
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import (
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"bytes"
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"fmt"
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"sort"
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"github.com/zclconf/go-cty/cty"
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)
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// MismatchMessage is a helper to return an English-language description of
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// the differences between got and want, phrased as a reason why got does
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// not conform to want.
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//
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// This function does not itself attempt conversion, and so it should generally
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// be used only after a conversion has failed, to report the conversion failure
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// to an English-speaking user. The result will be confusing got is actually
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// conforming to or convertable to want.
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//
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// The shorthand helper function Convert uses this function internally to
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// produce its error messages, so callers of that function do not need to
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// also use MismatchMessage.
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//
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// This function is similar to Type.TestConformance, but it is tailored to
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// describing conversion failures and so the messages it generates relate
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// specifically to the conversion rules implemented in this package.
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func MismatchMessage(got, want cty.Type) string {
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switch {
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case got.IsObjectType() && want.IsObjectType():
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// If both types are object types then we may be able to say something
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// about their respective attributes.
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return mismatchMessageObjects(got, want)
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case got.IsTupleType() && want.IsListType() && want.ElementType() == cty.DynamicPseudoType:
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// If conversion from tuple to list failed then it's because we couldn't
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// find a common type to convert all of the tuple elements to.
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return "all list elements must have the same type"
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case got.IsTupleType() && want.IsSetType() && want.ElementType() == cty.DynamicPseudoType:
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// If conversion from tuple to set failed then it's because we couldn't
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// find a common type to convert all of the tuple elements to.
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return "all set elements must have the same type"
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case got.IsObjectType() && want.IsMapType() && want.ElementType() == cty.DynamicPseudoType:
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// If conversion from object to map failed then it's because we couldn't
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// find a common type to convert all of the object attributes to.
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return "all map elements must have the same type"
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default:
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// If we have nothing better to say, we'll just state what was required.
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return want.FriendlyNameForConstraint() + " required"
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}
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}
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func mismatchMessageObjects(got, want cty.Type) string {
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// Per our conversion rules, "got" is allowed to be a superset of "want",
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// and so we'll produce error messages here under that assumption.
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gotAtys := got.AttributeTypes()
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wantAtys := want.AttributeTypes()
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// If we find missing attributes then we'll report those in preference,
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// but if not then we will report a maximum of one non-conforming
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// attribute, just to keep our messages relatively terse.
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// We'll also prefer to report a recursive type error from an _unsafe_
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// conversion over a safe one, because these are subjectively more
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// "serious".
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var missingAttrs []string
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var unsafeMismatchAttr string
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var safeMismatchAttr string
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for name, wantAty := range wantAtys {
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gotAty, exists := gotAtys[name]
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if !exists {
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missingAttrs = append(missingAttrs, name)
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continue
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}
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// We'll now try to convert these attributes in isolation and
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// see if we have a nested conversion error to report.
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// We'll try an unsafe conversion first, and then fall back on
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// safe if unsafe is possible.
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// If we already have an unsafe mismatch attr error then we won't bother
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// hunting for another one.
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if unsafeMismatchAttr != "" {
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continue
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}
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if conv := GetConversionUnsafe(gotAty, wantAty); conv == nil {
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unsafeMismatchAttr = fmt.Sprintf("attribute %q: %s", name, MismatchMessage(gotAty, wantAty))
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}
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// If we already have a safe mismatch attr error then we won't bother
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// hunting for another one.
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if safeMismatchAttr != "" {
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continue
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}
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if conv := GetConversion(gotAty, wantAty); conv == nil {
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safeMismatchAttr = fmt.Sprintf("attribute %q: %s", name, MismatchMessage(gotAty, wantAty))
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}
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}
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// We should now have collected at least one problem. If we have more than
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// one then we'll use our preference order to decide what is most important
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// to report.
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switch {
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case len(missingAttrs) != 0:
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switch len(missingAttrs) {
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case 1:
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return fmt.Sprintf("attribute %q is required", missingAttrs[0])
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case 2:
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return fmt.Sprintf("attributes %q and %q are required", missingAttrs[0], missingAttrs[1])
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default:
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sort.Strings(missingAttrs)
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var buf bytes.Buffer
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for _, name := range missingAttrs[:len(missingAttrs)-1] {
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fmt.Fprintf(&buf, "%q, ", name)
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}
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fmt.Fprintf(&buf, "and %q", missingAttrs[len(missingAttrs)-1])
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return fmt.Sprintf("attributes %s are required", buf.Bytes())
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}
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case unsafeMismatchAttr != "":
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return unsafeMismatchAttr
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case safeMismatchAttr != "":
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return safeMismatchAttr
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default:
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// We should never get here, but if we do then we'll return
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// just a generic message.
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return "incorrect object attributes"
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}
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}
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