Improve Nix Sourcing (#543)

## Summary
+ Don't rely on any binaries (like env) in order to source the nix
environment.
+ Don't pollute the environment with all sorts of variables, only source
the three we care about.
+ Use a well-tested library to parse the env variables

## How was it tested?
Removed nix from my path, used ubuntu container.

Author: loreto

go.mod

@@ -5,6 +5,7 @@ go 1.19
 require (
 	cuelang.org/go v0.4.3
 	github.com/AlecAivazis/survey/v2 v2.3.6
+	github.com/MakeNowJust/heredoc/v2 v2.0.1
 	github.com/alessio/shellescape v1.4.1
 	github.com/bmatcuk/doublestar/v4 v4.4.0
 	github.com/briandowns/spinner v1.19.0
@@ -16,6 +17,7 @@ require (
 	github.com/getsentry/sentry-go v0.17.0
 	github.com/google/go-cmp v0.5.9
 	github.com/google/uuid v1.3.0
+	github.com/hashicorp/go-envparse v0.1.0
 	github.com/imdario/mergo v0.3.13
 	github.com/mattn/go-isatty v0.0.16
 	github.com/mholt/archiver/v4 v4.0.0-alpha.7
@@ -61,5 +63,4 @@ require (
 	golang.org/x/sys v0.3.0 // indirect
 	golang.org/x/term v0.2.0 // indirect
 	golang.org/x/text v0.5.0 // indirect
-	gopkg.in/errgo.v2 v2.1.0 // indirect
 )

go.sum

@@ -2,6 +2,8 @@ cuelang.org/go v0.4.3 h1:W3oBBjDTm7+IZfCKZAmC8uDG0eYfJL4Pp/xbbCMKaVo=
 cuelang.org/go v0.4.3/go.mod h1:7805vR9H+VoBNdWFdI7jyDR3QLUPp4+naHfbcgp55HI=
 github.com/AlecAivazis/survey/v2 v2.3.6 h1:NvTuVHISgTHEHeBFqt6BHOe4Ny/NwGZr7w+F8S9ziyw=
 github.com/AlecAivazis/survey/v2 v2.3.6/go.mod h1:4AuI9b7RjAR+G7v9+C4YSlX/YL3K3cWNXgWXOhllqvI=
+github.com/MakeNowJust/heredoc/v2 v2.0.1 h1:rlCHh70XXXv7toz95ajQWOWQnN4WNLt0TdpZYIR/J6A=
+github.com/MakeNowJust/heredoc/v2 v2.0.1/go.mod h1:6/2Abh5s+hc3g9nbWLe9ObDIOhaRrqsyY9MWy+4JdRM=
 github.com/Netflix/go-expect v0.0.0-20220104043353-73e0943537d2 h1:+vx7roKuyA63nhn5WAunQHLTznkw5W8b1Xc0dNjp83s=
 github.com/Netflix/go-expect v0.0.0-20220104043353-73e0943537d2/go.mod h1:HBCaDeC1lPdgDeDbhX8XFpy1jqjK0IBG8W5K+xYqA0w=
 github.com/alessio/shellescape v1.4.1 h1:V7yhSDDn8LP4lc4jS8pFkt0zCnzVJlG5JXy9BVKJUX0=
@@ -48,6 +50,8 @@ github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/hashicorp/go-envparse v0.1.0 h1:bE++6bhIsNCPLvgDZkYqo3nA+/PFI51pkrHdmPSDFPY=
+github.com/hashicorp/go-envparse v0.1.0/go.mod h1:OHheN1GoygLlAkTlXLXvAdnXdZxy8JUweQ1rAXx1xnc=
 github.com/hinshun/vt10x v0.0.0-20220119200601-820417d04eec h1:qv2VnGeEQHchGaZ/u7lxST/RaJw+cv273q79D81Xbog=
 github.com/hinshun/vt10x v0.0.0-20220119200601-820417d04eec/go.mod h1:Q48J4R4DvxnHolD5P8pOtXigYlRuPLGl6moFx3ulM68=
 github.com/imdario/mergo v0.3.13 h1:lFzP57bqS/wsqKssCGmtLAb8A0wKjLGrve2q3PPVcBk=
@@ -63,9 +67,6 @@ github.com/klauspost/cpuid v1.2.0/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgo
 github.com/klauspost/pgzip v1.2.5 h1:qnWYvvKqedOF2ulHpMG72XQol4ILEJ8k2wwRl/Km8oE=
 github.com/klauspost/pgzip v1.2.5/go.mod h1:Ch1tH69qFZu15pkjo5kYi6mth2Zzwzt50oCQKQE9RUs=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
-github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
-github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/lib/pq v1.0.0 h1:X5PMW56eZitiTeO7tKzZxFCSpbFZJtkMMooicw2us9A=
 github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
@@ -99,8 +100,6 @@ github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/protocolbuffers/txtpbfmt v0.0.0-20201118171849-f6a6b3f636fc h1:gSVONBi2HWMFXCa9jFdYvYk7IwW/mTLxWOF7rXS4LO0=
-github.com/rogpeppe/go-internal v1.8.1 h1:geMPLpDpQOgVyCg5z5GoRwLHepNdb71NXb67XFkP+Eg=
-github.com/rogpeppe/go-internal v1.8.1/go.mod h1:JeRgkft04UBgHMgCIwADu4Pn6Mtm5d4nPKWu0nJ5d+o=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
@@ -152,10 +151,7 @@ golang.org/x/text v0.5.0 h1:OLmvp0KP+FVG99Ct/qFiL/Fhk4zp4QQnZ7b2U+5piUM=
 golang.org/x/text v0.5.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f h1:BLraFXnmrev5lT+xlilqcH8XK9/i0At2xKjWk4p6zsU=
-gopkg.in/errgo.v2 v2.1.0 h1:0vLT13EuvQ0hNvakwLuFZ/jYrLp5F3kcWHXdRggjCE8=
-gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.0/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

internal/nix/source.go

@@ -1,14 +1,14 @@
 package nix
 
 import (
-	"bufio"
 	"bytes"
-	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
 
+	"github.com/MakeNowJust/heredoc/v2"
+	"github.com/hashicorp/go-envparse"
 	"github.com/pkg/errors"
 )
 
@@ -26,27 +26,41 @@ func SourceNixEnv() error {
 		)
 	}
 
+	// Source the nix script that sets the environment, and print the environment
+	// variables that it sets, in a way we can parse.
+
+	// NOTE: Only use shell built-ins in this script so that we don't introduce
+	// any dependencies on an external binary.
+	script := heredoc.Docf(`
+		. %s;
+		echo PATH=$PATH;
+		echo NIX_PROFILES=$NIX_PROFILES;
+		echo NIX_SSL_CERT_FILE=$NIX_SSL_CERT_FILE;
+		echo MANPATH=$MANPATH;
+	`, srcFile)
 	cmd := exec.Command(
 		"/bin/sh",
 		"-c",
-		fmt.Sprintf(". %s ; echo '<<<ENVIRONMENT>>>' ; env", srcFile),
+		script,
 	)
 
 	bs, err := cmd.CombinedOutput()
 	if err != nil {
-		return errors.WithStack(err)
+		// When there's an error, the output is usually an error message that
+		// was printed to stderr and that we want in the error for debugging.
+		return errors.Wrap(err, string(bs))
+	}
+	envvars, err := envparse.Parse(bytes.NewReader(bs))
+
+	if err != nil {
+		return errors.Wrap(err, "failed to parse nix env vars")
 	}
-	s := bufio.NewScanner(bytes.NewReader(bs))
-	start := false
-	for s.Scan() {
-		if s.Text() == "<<<ENVIRONMENT>>>" {
-			start = true
-		} else if start {
-			kv := strings.SplitN(s.Text(), "=", 2)
-			if len(kv) == 2 {
-				os.Setenv(kv[0], kv[1])
-			}
+
+	for k, v := range envvars {
+		if len(strings.TrimSpace(v)) > 0 {
+			os.Setenv(k, v)
 		}
 	}
+
 	return nil
 }