SemVer

The semver package provides the ability to work with Semantic Versions in Go. Specifically it provides the ability to:

Parse semantic versions
Sort semantic versions
Check if a semantic version fits within a set of constraints
Optionally work with a v prefix

Parsing Semantic Versions

To parse a semantic version use the NewVersion function. For example,

    v, err := semver.NewVersion("1.2.3-beta.1+build345")

If there is an error the version wasn't parseable. The version object has methods to get the parts of the version, compare it to other versions, convert the version back into a string, and get the original string. For more details please see the documentation.

Sorting Semantic Versions

A set of versions can be sorted using the sort package from the standard library. For example,

    raw := []string{"1.2.3", "1.0", "1.3", "2", "0.4.2",}
    vs := make([]*semver.Version, len(raw))
	for i, r := range raw {
		v, err := semver.NewVersion(r)
		if err != nil {
			t.Errorf("Error parsing version: %s", err)
		}

		vs[i] = v
	}

	sort.Sort(semver.Collection(vs))

Checking Version Constraints

Checking a version against version constraints is one of the most featureful parts of the package.

    c, err := semver.NewConstraint(">= 1.2.3")
    if err != nil {
        // Handle constraint not being parseable.
    }

    v, _ := semver.NewVersion("1.3")
    if err != nil {
        // Handle version not being parseable.
    }
    // Check if the version meets the constraints. The a variable will be true.
    a := c.Check(v)

Basic Comparisons

There are two elements to the comparisons. First, a comparison string is a list of comma separated and comparisons. These are then separated by || separated or comparisons. For example, ">= 1.2, < 3.0.0 || >= 4.2.3" is looking for a comparison that's greater than or equal to 1.2 and less than 3.0.0 or is greater than or equal to 4.2.3.

The basic comparisons are:

=: equal (aliased to no operator)
!=: not equal
>: greater than
<: less than
>=: greater than or equal to
<=: less than or equal to

Note, according to the Semantic Version specification pre-releases may not be API compliant with their release counterpart. It says,

A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version.

SemVer comparisons without a pre-release value will skip pre-release versions. For example, >1.2.3 will skip pre-releases when looking at a list of values while >1.2.3-alpha.1 will evaluate pre-releases.

Hyphen Range Comparisons

There are multiple methods to handle ranges and the first is hyphens ranges. These look like:

1.2 - 1.4.5 which is equivalent to >= 1.2, <= 1.4.5
2.3.4 - 4.5 which is equivalent to >= 2.3.4, <= 4.5

Wildcards In Comparisons

The x, X, and * characters can be used as a wildcard character. This works for all comparison operators. When used on the = operator it falls back to the pack level comparison (see tilde below). For example,

1.2.x is equivalent to >= 1.2.0, < 1.3.0
>= 1.2.x is equivalent to >= 1.2.0
<= 2.x is equivalent to <= 3
* is equivalent to >= 0.0.0

Tilde Range Comparisons (Patch)

The tilde (~) comparison operator is for patch level ranges when a minor version is specified and major level changes when the minor number is missing. For example,

~1.2.3 is equivalent to >= 1.2.3, < 1.3.0
~1 is equivalent to >= 1, < 2
~2.3 is equivalent to >= 2.3, < 2.4
~1.2.x is equivalent to >= 1.2.0, < 1.3.0
~1.x is equivalent to >= 1, < 2

Caret Range Comparisons (Major)

The caret (^) comparison operator is for major level changes. This is useful when comparisons of API versions as a major change is API breaking. For example,

^1.2.3 is equivalent to >= 1.2.3, < 2.0.0
^1.2.x is equivalent to >= 1.2.0, < 2.0.0
^2.3 is equivalent to >= 2.3, < 3
^2.x is equivalent to >= 2.0.0, < 3

Validation

In addition to testing a version against a constraint, a version can be validated against a constraint. When validation fails a slice of errors containing why a version didn't meet the constraint is returned. For example,

    c, err := semver.NewConstraint("<= 1.2.3, >= 1.4")
    if err != nil {
        // Handle constraint not being parseable.
    }

    v, _ := semver.NewVersion("1.3")
    if err != nil {
        // Handle version not being parseable.
    }

    // Validate a version against a constraint.
    a, msgs := c.Validate(v)
    // a is false
    for _, m := range msgs {
        fmt.Println(m)

        // Loops over the errors which would read
        // "1.3 is greater than 1.2.3"
        // "1.3 is less than 1.4"
    }

Contribute

If you find an issue or want to contribute please file an issue or create a pull request.

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