standard library: add log commands (#8448)

# Description

```nushell
log critical "this is a critical message"
log error "this is an error message"
log warning "this is a warning message"
log info "this is an info message"
log debug "this is a debug message"
```


![image](https://user-images.githubusercontent.com/282320/225071852-1ddf0e87-d12b-452d-9598-5122df7123ab.png)

# Tests + Formatting

Tests are written. To run automatically, #8443 needs to be merged before
or after this PR.

---------

Co-authored-by: Mate Farkas <Mate.Farkas@oneidentity.com>

crates/nu-utils/standard_library/README.md

@@ -60,13 +60,13 @@ use /path/to/standard_library/std.nu
 ### :test_tube: run the tests
 the following call should return no errors
 ```bash
-nu /path/to/standard_library/tests.nu
+NU_LOG_LEVEL=DEBUG nu /path/to/standard_library/tests.nu
 ```
 
 > #### :mag: a concrete example
 > with `STD_LIB` defined as in the example above
 > ```bash
-> nu ($env.STD_LIB | path join "tests.nu")
+> NU_LOG_LEVEL=DEBUG nu ($env.STD_LIB | path join "tests.nu")
 > ```
 
 [REPL]: https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop

crates/nu-utils/standard_library/std.nu

@@ -236,3 +236,63 @@ def-env  _fetch [
 
     cd ($env.DIRS_LIST | get $pos )
 }
+
+def CRITICAL_LEVEL [] { 50 }
+def ERROR_LEVEL    [] { 40 }
+def WARNING_LEVEL  [] { 30 }
+def INFO_LEVEL     [] { 20 }
+def DEBUG_LEVEL    [] { 10 }
+
+def parse-string-level [level: string] {
+    (
+        if $level == "CRITICAL" { (CRITICAL_LEVEL)}
+        else if $level == "CRIT" { (CRITICAL_LEVEL)}
+        else if $level == "ERROR" { (ERROR_LEVEL) }
+        else if $level == "WARNING" { (WARNING_LEVEL) }
+        else if $level == "WARN" { (WARNING_LEVEL) }
+        else if $level == "INFO" { (INFO_LEVEL) }
+        else if $level == "DEBUG" { (DEBUG_LEVEL) }
+        else { (INFO_LEVEL) }
+    )
+}
+
+def current-log-level [] {
+    let env_level = ($env | get -i NU_LOG_LEVEL | default (INFO_LEVEL))
+
+    try {
+        ($env_level | into int)
+    } catch {
+        parse-string-level $env_level
+    }
+}
+
+# Log critical message
+export def "log critical" [message: string] {
+    if (current-log-level) > (CRITICAL_LEVEL) { return }
+
+    print --stderr $"(ansi red_bold)CRIT  ($message)(ansi reset)"
+}
+# Log error message
+export def "log error" [message: string] {
+    if (current-log-level) > (ERROR_LEVEL) { return }
+
+    print --stderr $"(ansi red)ERROR ($message)(ansi reset)"
+}
+# Log warning message
+export def "log warning" [message: string] {
+    if (current-log-level) > (WARNING_LEVEL) { return }
+
+    print --stderr $"(ansi yellow)WARN  ($message)(ansi reset)"
+}
+# Log info message
+export def "log info" [message: string] {
+    if (current-log-level) > (INFO_LEVEL) { return }
+
+    print --stderr $"(ansi white)INFO  ($message)(ansi reset)"
+}
+# Log debug message
+export def "log debug" [message: string] {
+    if (current-log-level) > (DEBUG_LEVEL) { return }
+
+    print --stderr $"(ansi default_dimmed)DEBUG ($message)(ansi reset)"
+}

crates/nu-utils/standard_library/test_logger.nu

@@ -0,0 +1,39 @@
+use std.nu *
+
+def run [system_level, message_level] {
+    cd $env.FILE_PWD
+    do {
+        nu -c $'use std.nu; NU_LOG_LEVEL=($system_level) std log ($message_level) "test message"' 
+    } | complete | get -i stderr
+}
+def "assert no message" [system_level, message_level] {
+    let output = (run $system_level $message_level)
+    assert eq $output ""
+}
+
+def "assert message" [system_level, message_level, message_level_str] {
+    let output = (run $system_level $message_level)
+    assert ($output | str contains $message_level_str)
+    assert ($output | str contains "test message")
+}
+
+export def test_critical [] {
+    assert no message 99 critical
+    assert message CRITICAL critical CRIT
+}
+export def test_error [] {
+    assert no message CRITICAL error 
+    assert message ERROR error ERROR
+}
+export def test_warning [] {
+    assert no message ERROR warning 
+    assert message  WARNING warning WARN
+}
+export def test_info [] {
+    assert no message WARNING info 
+    assert message  INFO info INFO
+}
+export def test_debug [] {
+    assert no message INFO debug 
+    assert message  DEBUG debug DEBUG
+}

crates/nu-utils/standard_library/tests.nu

@@ -1,10 +1,12 @@
+use std.nu *
+
 def main [] {
     for test_file in (ls ($env.FILE_PWD | path join "test_*.nu") -f | get name) {
         let $module_name = ($test_file | path parse).stem
 
-        echo $"(ansi default)INFO  Run tests in ($module_name)(ansi reset)"
+        log info $"Run tests in ($module_name) module"
         let tests = (
-            nu -c $'use ($test_file) *; $nu.scope.commands | to nuon'
+            nu -c $'use ($test_file) *; $nu.scope.commands | select name module_name | to nuon'
             | from nuon
             | where module_name == $module_name
             | where ($it.name | str starts-with "test_")
@@ -12,7 +14,7 @@ def main [] {
         )
 
         for test_case in $tests {
-            echo $"(ansi default_dimmed)DEBUG Run test ($module_name)/($test_case)(ansi reset)"
+            log debug $"Run test ($module_name) ($test_case)"
             nu -c $'use ($test_file) ($test_case); ($test_case)'
         }
     }